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Linux/mm/migrate.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  * Memory Migration functionality - linux/mm/migrate.c
  4  *
  5  * Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter
  6  *
  7  * Page migration was first developed in the context of the memory hotplug
  8  * project. The main authors of the migration code are:
  9  *
 10  * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
 11  * Hirokazu Takahashi <taka@valinux.co.jp>
 12  * Dave Hansen <haveblue@us.ibm.com>
 13  * Christoph Lameter
 14  */
 15 
 16 #include <linux/migrate.h>
 17 #include <linux/export.h>
 18 #include <linux/swap.h>
 19 #include <linux/swapops.h>
 20 #include <linux/pagemap.h>
 21 #include <linux/buffer_head.h>
 22 #include <linux/mm_inline.h>
 23 #include <linux/nsproxy.h>
 24 #include <linux/pagevec.h>
 25 #include <linux/ksm.h>
 26 #include <linux/rmap.h>
 27 #include <linux/topology.h>
 28 #include <linux/cpu.h>
 29 #include <linux/cpuset.h>
 30 #include <linux/writeback.h>
 31 #include <linux/mempolicy.h>
 32 #include <linux/vmalloc.h>
 33 #include <linux/security.h>
 34 #include <linux/backing-dev.h>
 35 #include <linux/compaction.h>
 36 #include <linux/syscalls.h>
 37 #include <linux/hugetlb.h>
 38 #include <linux/hugetlb_cgroup.h>
 39 #include <linux/gfp.h>
 40 #include <linux/pfn_t.h>
 41 #include <linux/memremap.h>
 42 #include <linux/userfaultfd_k.h>
 43 #include <linux/balloon_compaction.h>
 44 #include <linux/mmu_notifier.h>
 45 #include <linux/page_idle.h>
 46 #include <linux/page_owner.h>
 47 #include <linux/sched/mm.h>
 48 #include <linux/ptrace.h>
 49 
 50 #include <asm/tlbflush.h>
 51 
 52 #define CREATE_TRACE_POINTS
 53 #include <trace/events/migrate.h>
 54 
 55 #include "internal.h"
 56 
 57 /*
 58  * migrate_prep() needs to be called before we start compiling a list of pages
 59  * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
 60  * undesirable, use migrate_prep_local()
 61  */
 62 int migrate_prep(void)
 63 {
 64         /*
 65          * Clear the LRU lists so pages can be isolated.
 66          * Note that pages may be moved off the LRU after we have
 67          * drained them. Those pages will fail to migrate like other
 68          * pages that may be busy.
 69          */
 70         lru_add_drain_all();
 71 
 72         return 0;
 73 }
 74 
 75 /* Do the necessary work of migrate_prep but not if it involves other CPUs */
 76 int migrate_prep_local(void)
 77 {
 78         lru_add_drain();
 79 
 80         return 0;
 81 }
 82 
 83 int isolate_movable_page(struct page *page, isolate_mode_t mode)
 84 {
 85         struct address_space *mapping;
 86 
 87         /*
 88          * Avoid burning cycles with pages that are yet under __free_pages(),
 89          * or just got freed under us.
 90          *
 91          * In case we 'win' a race for a movable page being freed under us and
 92          * raise its refcount preventing __free_pages() from doing its job
 93          * the put_page() at the end of this block will take care of
 94          * release this page, thus avoiding a nasty leakage.
 95          */
 96         if (unlikely(!get_page_unless_zero(page)))
 97                 goto out;
 98 
 99         /*
100          * Check PageMovable before holding a PG_lock because page's owner
101          * assumes anybody doesn't touch PG_lock of newly allocated page
102          * so unconditionally grapping the lock ruins page's owner side.
103          */
104         if (unlikely(!__PageMovable(page)))
105                 goto out_putpage;
106         /*
107          * As movable pages are not isolated from LRU lists, concurrent
108          * compaction threads can race against page migration functions
109          * as well as race against the releasing a page.
110          *
111          * In order to avoid having an already isolated movable page
112          * being (wrongly) re-isolated while it is under migration,
113          * or to avoid attempting to isolate pages being released,
114          * lets be sure we have the page lock
115          * before proceeding with the movable page isolation steps.
116          */
117         if (unlikely(!trylock_page(page)))
118                 goto out_putpage;
119 
120         if (!PageMovable(page) || PageIsolated(page))
121                 goto out_no_isolated;
122 
123         mapping = page_mapping(page);
124         VM_BUG_ON_PAGE(!mapping, page);
125 
126         if (!mapping->a_ops->isolate_page(page, mode))
127                 goto out_no_isolated;
128 
129         /* Driver shouldn't use PG_isolated bit of page->flags */
130         WARN_ON_ONCE(PageIsolated(page));
131         __SetPageIsolated(page);
132         unlock_page(page);
133 
134         return 0;
135 
136 out_no_isolated:
137         unlock_page(page);
138 out_putpage:
139         put_page(page);
140 out:
141         return -EBUSY;
142 }
143 
144 /* It should be called on page which is PG_movable */
145 void putback_movable_page(struct page *page)
146 {
147         struct address_space *mapping;
148 
149         VM_BUG_ON_PAGE(!PageLocked(page), page);
150         VM_BUG_ON_PAGE(!PageMovable(page), page);
151         VM_BUG_ON_PAGE(!PageIsolated(page), page);
152 
153         mapping = page_mapping(page);
154         mapping->a_ops->putback_page(page);
155         __ClearPageIsolated(page);
156 }
157 
158 /*
159  * Put previously isolated pages back onto the appropriate lists
160  * from where they were once taken off for compaction/migration.
161  *
162  * This function shall be used whenever the isolated pageset has been
163  * built from lru, balloon, hugetlbfs page. See isolate_migratepages_range()
164  * and isolate_huge_page().
165  */
166 void putback_movable_pages(struct list_head *l)
167 {
168         struct page *page;
169         struct page *page2;
170 
171         list_for_each_entry_safe(page, page2, l, lru) {
172                 if (unlikely(PageHuge(page))) {
173                         putback_active_hugepage(page);
174                         continue;
175                 }
176                 list_del(&page->lru);
177                 /*
178                  * We isolated non-lru movable page so here we can use
179                  * __PageMovable because LRU page's mapping cannot have
180                  * PAGE_MAPPING_MOVABLE.
181                  */
182                 if (unlikely(__PageMovable(page))) {
183                         VM_BUG_ON_PAGE(!PageIsolated(page), page);
184                         lock_page(page);
185                         if (PageMovable(page))
186                                 putback_movable_page(page);
187                         else
188                                 __ClearPageIsolated(page);
189                         unlock_page(page);
190                         put_page(page);
191                 } else {
192                         mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON +
193                                         page_is_file_cache(page), -hpage_nr_pages(page));
194                         putback_lru_page(page);
195                 }
196         }
197 }
198 
199 /*
200  * Restore a potential migration pte to a working pte entry
201  */
202 static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma,
203                                  unsigned long addr, void *old)
204 {
205         struct page_vma_mapped_walk pvmw = {
206                 .page = old,
207                 .vma = vma,
208                 .address = addr,
209                 .flags = PVMW_SYNC | PVMW_MIGRATION,
210         };
211         struct page *new;
212         pte_t pte;
213         swp_entry_t entry;
214 
215         VM_BUG_ON_PAGE(PageTail(page), page);
216         while (page_vma_mapped_walk(&pvmw)) {
217                 if (PageKsm(page))
218                         new = page;
219                 else
220                         new = page - pvmw.page->index +
221                                 linear_page_index(vma, pvmw.address);
222 
223 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
224                 /* PMD-mapped THP migration entry */
225                 if (!pvmw.pte) {
226                         VM_BUG_ON_PAGE(PageHuge(page) || !PageTransCompound(page), page);
227                         remove_migration_pmd(&pvmw, new);
228                         continue;
229                 }
230 #endif
231 
232                 get_page(new);
233                 pte = pte_mkold(mk_pte(new, READ_ONCE(vma->vm_page_prot)));
234                 if (pte_swp_soft_dirty(*pvmw.pte))
235                         pte = pte_mksoft_dirty(pte);
236 
237                 /*
238                  * Recheck VMA as permissions can change since migration started
239                  */
240                 entry = pte_to_swp_entry(*pvmw.pte);
241                 if (is_write_migration_entry(entry))
242                         pte = maybe_mkwrite(pte, vma);
243 
244                 if (unlikely(is_zone_device_page(new))) {
245                         if (is_device_private_page(new)) {
246                                 entry = make_device_private_entry(new, pte_write(pte));
247                                 pte = swp_entry_to_pte(entry);
248                         } else if (is_device_public_page(new)) {
249                                 pte = pte_mkdevmap(pte);
250                                 flush_dcache_page(new);
251                         }
252                 } else
253                         flush_dcache_page(new);
254 
255 #ifdef CONFIG_HUGETLB_PAGE
256                 if (PageHuge(new)) {
257                         pte = pte_mkhuge(pte);
258                         pte = arch_make_huge_pte(pte, vma, new, 0);
259                         set_huge_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
260                         if (PageAnon(new))
261                                 hugepage_add_anon_rmap(new, vma, pvmw.address);
262                         else
263                                 page_dup_rmap(new, true);
264                 } else
265 #endif
266                 {
267                         set_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
268 
269                         if (PageAnon(new))
270                                 page_add_anon_rmap(new, vma, pvmw.address, false);
271                         else
272                                 page_add_file_rmap(new, false);
273                 }
274                 if (vma->vm_flags & VM_LOCKED && !PageTransCompound(new))
275                         mlock_vma_page(new);
276 
277                 /* No need to invalidate - it was non-present before */
278                 update_mmu_cache(vma, pvmw.address, pvmw.pte);
279         }
280 
281         return true;
282 }
283 
284 /*
285  * Get rid of all migration entries and replace them by
286  * references to the indicated page.
287  */
288 void remove_migration_ptes(struct page *old, struct page *new, bool locked)
289 {
290         struct rmap_walk_control rwc = {
291                 .rmap_one = remove_migration_pte,
292                 .arg = old,
293         };
294 
295         if (locked)
296                 rmap_walk_locked(new, &rwc);
297         else
298                 rmap_walk(new, &rwc);
299 }
300 
301 /*
302  * Something used the pte of a page under migration. We need to
303  * get to the page and wait until migration is finished.
304  * When we return from this function the fault will be retried.
305  */
306 void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
307                                 spinlock_t *ptl)
308 {
309         pte_t pte;
310         swp_entry_t entry;
311         struct page *page;
312 
313         spin_lock(ptl);
314         pte = *ptep;
315         if (!is_swap_pte(pte))
316                 goto out;
317 
318         entry = pte_to_swp_entry(pte);
319         if (!is_migration_entry(entry))
320                 goto out;
321 
322         page = migration_entry_to_page(entry);
323 
324         /*
325          * Once radix-tree replacement of page migration started, page_count
326          * *must* be zero. And, we don't want to call wait_on_page_locked()
327          * against a page without get_page().
328          * So, we use get_page_unless_zero(), here. Even failed, page fault
329          * will occur again.
330          */
331         if (!get_page_unless_zero(page))
332                 goto out;
333         pte_unmap_unlock(ptep, ptl);
334         wait_on_page_locked(page);
335         put_page(page);
336         return;
337 out:
338         pte_unmap_unlock(ptep, ptl);
339 }
340 
341 void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
342                                 unsigned long address)
343 {
344         spinlock_t *ptl = pte_lockptr(mm, pmd);
345         pte_t *ptep = pte_offset_map(pmd, address);
346         __migration_entry_wait(mm, ptep, ptl);
347 }
348 
349 void migration_entry_wait_huge(struct vm_area_struct *vma,
350                 struct mm_struct *mm, pte_t *pte)
351 {
352         spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), mm, pte);
353         __migration_entry_wait(mm, pte, ptl);
354 }
355 
356 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
357 void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
358 {
359         spinlock_t *ptl;
360         struct page *page;
361 
362         ptl = pmd_lock(mm, pmd);
363         if (!is_pmd_migration_entry(*pmd))
364                 goto unlock;
365         page = migration_entry_to_page(pmd_to_swp_entry(*pmd));
366         if (!get_page_unless_zero(page))
367                 goto unlock;
368         spin_unlock(ptl);
369         wait_on_page_locked(page);
370         put_page(page);
371         return;
372 unlock:
373         spin_unlock(ptl);
374 }
375 #endif
376 
377 #ifdef CONFIG_BLOCK
378 /* Returns true if all buffers are successfully locked */
379 static bool buffer_migrate_lock_buffers(struct buffer_head *head,
380                                                         enum migrate_mode mode)
381 {
382         struct buffer_head *bh = head;
383 
384         /* Simple case, sync compaction */
385         if (mode != MIGRATE_ASYNC) {
386                 do {
387                         get_bh(bh);
388                         lock_buffer(bh);
389                         bh = bh->b_this_page;
390 
391                 } while (bh != head);
392 
393                 return true;
394         }
395 
396         /* async case, we cannot block on lock_buffer so use trylock_buffer */
397         do {
398                 get_bh(bh);
399                 if (!trylock_buffer(bh)) {
400                         /*
401                          * We failed to lock the buffer and cannot stall in
402                          * async migration. Release the taken locks
403                          */
404                         struct buffer_head *failed_bh = bh;
405                         put_bh(failed_bh);
406                         bh = head;
407                         while (bh != failed_bh) {
408                                 unlock_buffer(bh);
409                                 put_bh(bh);
410                                 bh = bh->b_this_page;
411                         }
412                         return false;
413                 }
414 
415                 bh = bh->b_this_page;
416         } while (bh != head);
417         return true;
418 }
419 #else
420 static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
421                                                         enum migrate_mode mode)
422 {
423         return true;
424 }
425 #endif /* CONFIG_BLOCK */
426 
427 /*
428  * Replace the page in the mapping.
429  *
430  * The number of remaining references must be:
431  * 1 for anonymous pages without a mapping
432  * 2 for pages with a mapping
433  * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
434  */
435 int migrate_page_move_mapping(struct address_space *mapping,
436                 struct page *newpage, struct page *page,
437                 struct buffer_head *head, enum migrate_mode mode,
438                 int extra_count)
439 {
440         struct zone *oldzone, *newzone;
441         int dirty;
442         int expected_count = 1 + extra_count;
443         void **pslot;
444 
445         /*
446          * Device public or private pages have an extra refcount as they are
447          * ZONE_DEVICE pages.
448          */
449         expected_count += is_device_private_page(page);
450         expected_count += is_device_public_page(page);
451 
452         if (!mapping) {
453                 /* Anonymous page without mapping */
454                 if (page_count(page) != expected_count)
455                         return -EAGAIN;
456 
457                 /* No turning back from here */
458                 newpage->index = page->index;
459                 newpage->mapping = page->mapping;
460                 if (PageSwapBacked(page))
461                         __SetPageSwapBacked(newpage);
462 
463                 return MIGRATEPAGE_SUCCESS;
464         }
465 
466         oldzone = page_zone(page);
467         newzone = page_zone(newpage);
468 
469         spin_lock_irq(&mapping->tree_lock);
470 
471         pslot = radix_tree_lookup_slot(&mapping->page_tree,
472                                         page_index(page));
473 
474         expected_count += 1 + page_has_private(page);
475         if (page_count(page) != expected_count ||
476                 radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
477                 spin_unlock_irq(&mapping->tree_lock);
478                 return -EAGAIN;
479         }
480 
481         if (!page_ref_freeze(page, expected_count)) {
482                 spin_unlock_irq(&mapping->tree_lock);
483                 return -EAGAIN;
484         }
485 
486         /*
487          * In the async migration case of moving a page with buffers, lock the
488          * buffers using trylock before the mapping is moved. If the mapping
489          * was moved, we later failed to lock the buffers and could not move
490          * the mapping back due to an elevated page count, we would have to
491          * block waiting on other references to be dropped.
492          */
493         if (mode == MIGRATE_ASYNC && head &&
494                         !buffer_migrate_lock_buffers(head, mode)) {
495                 page_ref_unfreeze(page, expected_count);
496                 spin_unlock_irq(&mapping->tree_lock);
497                 return -EAGAIN;
498         }
499 
500         /*
501          * Now we know that no one else is looking at the page:
502          * no turning back from here.
503          */
504         newpage->index = page->index;
505         newpage->mapping = page->mapping;
506         get_page(newpage);      /* add cache reference */
507         if (PageSwapBacked(page)) {
508                 __SetPageSwapBacked(newpage);
509                 if (PageSwapCache(page)) {
510                         SetPageSwapCache(newpage);
511                         set_page_private(newpage, page_private(page));
512                 }
513         } else {
514                 VM_BUG_ON_PAGE(PageSwapCache(page), page);
515         }
516 
517         /* Move dirty while page refs frozen and newpage not yet exposed */
518         dirty = PageDirty(page);
519         if (dirty) {
520                 ClearPageDirty(page);
521                 SetPageDirty(newpage);
522         }
523 
524         radix_tree_replace_slot(&mapping->page_tree, pslot, newpage);
525 
526         /*
527          * Drop cache reference from old page by unfreezing
528          * to one less reference.
529          * We know this isn't the last reference.
530          */
531         page_ref_unfreeze(page, expected_count - 1);
532 
533         spin_unlock(&mapping->tree_lock);
534         /* Leave irq disabled to prevent preemption while updating stats */
535 
536         /*
537          * If moved to a different zone then also account
538          * the page for that zone. Other VM counters will be
539          * taken care of when we establish references to the
540          * new page and drop references to the old page.
541          *
542          * Note that anonymous pages are accounted for
543          * via NR_FILE_PAGES and NR_ANON_MAPPED if they
544          * are mapped to swap space.
545          */
546         if (newzone != oldzone) {
547                 __dec_node_state(oldzone->zone_pgdat, NR_FILE_PAGES);
548                 __inc_node_state(newzone->zone_pgdat, NR_FILE_PAGES);
549                 if (PageSwapBacked(page) && !PageSwapCache(page)) {
550                         __dec_node_state(oldzone->zone_pgdat, NR_SHMEM);
551                         __inc_node_state(newzone->zone_pgdat, NR_SHMEM);
552                 }
553                 if (dirty && mapping_cap_account_dirty(mapping)) {
554                         __dec_node_state(oldzone->zone_pgdat, NR_FILE_DIRTY);
555                         __dec_zone_state(oldzone, NR_ZONE_WRITE_PENDING);
556                         __inc_node_state(newzone->zone_pgdat, NR_FILE_DIRTY);
557                         __inc_zone_state(newzone, NR_ZONE_WRITE_PENDING);
558                 }
559         }
560         local_irq_enable();
561 
562         return MIGRATEPAGE_SUCCESS;
563 }
564 EXPORT_SYMBOL(migrate_page_move_mapping);
565 
566 /*
567  * The expected number of remaining references is the same as that
568  * of migrate_page_move_mapping().
569  */
570 int migrate_huge_page_move_mapping(struct address_space *mapping,
571                                    struct page *newpage, struct page *page)
572 {
573         int expected_count;
574         void **pslot;
575 
576         spin_lock_irq(&mapping->tree_lock);
577 
578         pslot = radix_tree_lookup_slot(&mapping->page_tree,
579                                         page_index(page));
580 
581         expected_count = 2 + page_has_private(page);
582         if (page_count(page) != expected_count ||
583                 radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
584                 spin_unlock_irq(&mapping->tree_lock);
585                 return -EAGAIN;
586         }
587 
588         if (!page_ref_freeze(page, expected_count)) {
589                 spin_unlock_irq(&mapping->tree_lock);
590                 return -EAGAIN;
591         }
592 
593         newpage->index = page->index;
594         newpage->mapping = page->mapping;
595 
596         get_page(newpage);
597 
598         radix_tree_replace_slot(&mapping->page_tree, pslot, newpage);
599 
600         page_ref_unfreeze(page, expected_count - 1);
601 
602         spin_unlock_irq(&mapping->tree_lock);
603 
604         return MIGRATEPAGE_SUCCESS;
605 }
606 
607 /*
608  * Gigantic pages are so large that we do not guarantee that page++ pointer
609  * arithmetic will work across the entire page.  We need something more
610  * specialized.
611  */
612 static void __copy_gigantic_page(struct page *dst, struct page *src,
613                                 int nr_pages)
614 {
615         int i;
616         struct page *dst_base = dst;
617         struct page *src_base = src;
618 
619         for (i = 0; i < nr_pages; ) {
620                 cond_resched();
621                 copy_highpage(dst, src);
622 
623                 i++;
624                 dst = mem_map_next(dst, dst_base, i);
625                 src = mem_map_next(src, src_base, i);
626         }
627 }
628 
629 static void copy_huge_page(struct page *dst, struct page *src)
630 {
631         int i;
632         int nr_pages;
633 
634         if (PageHuge(src)) {
635                 /* hugetlbfs page */
636                 struct hstate *h = page_hstate(src);
637                 nr_pages = pages_per_huge_page(h);
638 
639                 if (unlikely(nr_pages > MAX_ORDER_NR_PAGES)) {
640                         __copy_gigantic_page(dst, src, nr_pages);
641                         return;
642                 }
643         } else {
644                 /* thp page */
645                 BUG_ON(!PageTransHuge(src));
646                 nr_pages = hpage_nr_pages(src);
647         }
648 
649         for (i = 0; i < nr_pages; i++) {
650                 cond_resched();
651                 copy_highpage(dst + i, src + i);
652         }
653 }
654 
655 /*
656  * Copy the page to its new location
657  */
658 void migrate_page_states(struct page *newpage, struct page *page)
659 {
660         int cpupid;
661 
662         if (PageError(page))
663                 SetPageError(newpage);
664         if (PageReferenced(page))
665                 SetPageReferenced(newpage);
666         if (PageUptodate(page))
667                 SetPageUptodate(newpage);
668         if (TestClearPageActive(page)) {
669                 VM_BUG_ON_PAGE(PageUnevictable(page), page);
670                 SetPageActive(newpage);
671         } else if (TestClearPageUnevictable(page))
672                 SetPageUnevictable(newpage);
673         if (PageChecked(page))
674                 SetPageChecked(newpage);
675         if (PageMappedToDisk(page))
676                 SetPageMappedToDisk(newpage);
677 
678         /* Move dirty on pages not done by migrate_page_move_mapping() */
679         if (PageDirty(page))
680                 SetPageDirty(newpage);
681 
682         if (page_is_young(page))
683                 set_page_young(newpage);
684         if (page_is_idle(page))
685                 set_page_idle(newpage);
686 
687         /*
688          * Copy NUMA information to the new page, to prevent over-eager
689          * future migrations of this same page.
690          */
691         cpupid = page_cpupid_xchg_last(page, -1);
692         page_cpupid_xchg_last(newpage, cpupid);
693 
694         ksm_migrate_page(newpage, page);
695         /*
696          * Please do not reorder this without considering how mm/ksm.c's
697          * get_ksm_page() depends upon ksm_migrate_page() and PageSwapCache().
698          */
699         if (PageSwapCache(page))
700                 ClearPageSwapCache(page);
701         ClearPagePrivate(page);
702         set_page_private(page, 0);
703 
704         /*
705          * If any waiters have accumulated on the new page then
706          * wake them up.
707          */
708         if (PageWriteback(newpage))
709                 end_page_writeback(newpage);
710 
711         copy_page_owner(page, newpage);
712 
713         mem_cgroup_migrate(page, newpage);
714 }
715 EXPORT_SYMBOL(migrate_page_states);
716 
717 void migrate_page_copy(struct page *newpage, struct page *page)
718 {
719         if (PageHuge(page) || PageTransHuge(page))
720                 copy_huge_page(newpage, page);
721         else
722                 copy_highpage(newpage, page);
723 
724         migrate_page_states(newpage, page);
725 }
726 EXPORT_SYMBOL(migrate_page_copy);
727 
728 /************************************************************
729  *                    Migration functions
730  ***********************************************************/
731 
732 /*
733  * Common logic to directly migrate a single LRU page suitable for
734  * pages that do not use PagePrivate/PagePrivate2.
735  *
736  * Pages are locked upon entry and exit.
737  */
738 int migrate_page(struct address_space *mapping,
739                 struct page *newpage, struct page *page,
740                 enum migrate_mode mode)
741 {
742         int rc;
743 
744         BUG_ON(PageWriteback(page));    /* Writeback must be complete */
745 
746         rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
747 
748         if (rc != MIGRATEPAGE_SUCCESS)
749                 return rc;
750 
751         if (mode != MIGRATE_SYNC_NO_COPY)
752                 migrate_page_copy(newpage, page);
753         else
754                 migrate_page_states(newpage, page);
755         return MIGRATEPAGE_SUCCESS;
756 }
757 EXPORT_SYMBOL(migrate_page);
758 
759 #ifdef CONFIG_BLOCK
760 /*
761  * Migration function for pages with buffers. This function can only be used
762  * if the underlying filesystem guarantees that no other references to "page"
763  * exist.
764  */
765 int buffer_migrate_page(struct address_space *mapping,
766                 struct page *newpage, struct page *page, enum migrate_mode mode)
767 {
768         struct buffer_head *bh, *head;
769         int rc;
770 
771         if (!page_has_buffers(page))
772                 return migrate_page(mapping, newpage, page, mode);
773 
774         head = page_buffers(page);
775 
776         rc = migrate_page_move_mapping(mapping, newpage, page, head, mode, 0);
777 
778         if (rc != MIGRATEPAGE_SUCCESS)
779                 return rc;
780 
781         /*
782          * In the async case, migrate_page_move_mapping locked the buffers
783          * with an IRQ-safe spinlock held. In the sync case, the buffers
784          * need to be locked now
785          */
786         if (mode != MIGRATE_ASYNC)
787                 BUG_ON(!buffer_migrate_lock_buffers(head, mode));
788 
789         ClearPagePrivate(page);
790         set_page_private(newpage, page_private(page));
791         set_page_private(page, 0);
792         put_page(page);
793         get_page(newpage);
794 
795         bh = head;
796         do {
797                 set_bh_page(bh, newpage, bh_offset(bh));
798                 bh = bh->b_this_page;
799 
800         } while (bh != head);
801 
802         SetPagePrivate(newpage);
803 
804         if (mode != MIGRATE_SYNC_NO_COPY)
805                 migrate_page_copy(newpage, page);
806         else
807                 migrate_page_states(newpage, page);
808 
809         bh = head;
810         do {
811                 unlock_buffer(bh);
812                 put_bh(bh);
813                 bh = bh->b_this_page;
814 
815         } while (bh != head);
816 
817         return MIGRATEPAGE_SUCCESS;
818 }
819 EXPORT_SYMBOL(buffer_migrate_page);
820 #endif
821 
822 /*
823  * Writeback a page to clean the dirty state
824  */
825 static int writeout(struct address_space *mapping, struct page *page)
826 {
827         struct writeback_control wbc = {
828                 .sync_mode = WB_SYNC_NONE,
829                 .nr_to_write = 1,
830                 .range_start = 0,
831                 .range_end = LLONG_MAX,
832                 .for_reclaim = 1
833         };
834         int rc;
835 
836         if (!mapping->a_ops->writepage)
837                 /* No write method for the address space */
838                 return -EINVAL;
839 
840         if (!clear_page_dirty_for_io(page))
841                 /* Someone else already triggered a write */
842                 return -EAGAIN;
843 
844         /*
845          * A dirty page may imply that the underlying filesystem has
846          * the page on some queue. So the page must be clean for
847          * migration. Writeout may mean we loose the lock and the
848          * page state is no longer what we checked for earlier.
849          * At this point we know that the migration attempt cannot
850          * be successful.
851          */
852         remove_migration_ptes(page, page, false);
853 
854         rc = mapping->a_ops->writepage(page, &wbc);
855 
856         if (rc != AOP_WRITEPAGE_ACTIVATE)
857                 /* unlocked. Relock */
858                 lock_page(page);
859 
860         return (rc < 0) ? -EIO : -EAGAIN;
861 }
862 
863 /*
864  * Default handling if a filesystem does not provide a migration function.
865  */
866 static int fallback_migrate_page(struct address_space *mapping,
867         struct page *newpage, struct page *page, enum migrate_mode mode)
868 {
869         if (PageDirty(page)) {
870                 /* Only writeback pages in full synchronous migration */
871                 switch (mode) {
872                 case MIGRATE_SYNC:
873                 case MIGRATE_SYNC_NO_COPY:
874                         break;
875                 default:
876                         return -EBUSY;
877                 }
878                 return writeout(mapping, page);
879         }
880 
881         /*
882          * Buffers may be managed in a filesystem specific way.
883          * We must have no buffers or drop them.
884          */
885         if (page_has_private(page) &&
886             !try_to_release_page(page, GFP_KERNEL))
887                 return -EAGAIN;
888 
889         return migrate_page(mapping, newpage, page, mode);
890 }
891 
892 /*
893  * Move a page to a newly allocated page
894  * The page is locked and all ptes have been successfully removed.
895  *
896  * The new page will have replaced the old page if this function
897  * is successful.
898  *
899  * Return value:
900  *   < 0 - error code
901  *  MIGRATEPAGE_SUCCESS - success
902  */
903 static int move_to_new_page(struct page *newpage, struct page *page,
904                                 enum migrate_mode mode)
905 {
906         struct address_space *mapping;
907         int rc = -EAGAIN;
908         bool is_lru = !__PageMovable(page);
909 
910         VM_BUG_ON_PAGE(!PageLocked(page), page);
911         VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
912 
913         mapping = page_mapping(page);
914 
915         if (likely(is_lru)) {
916                 if (!mapping)
917                         rc = migrate_page(mapping, newpage, page, mode);
918                 else if (mapping->a_ops->migratepage)
919                         /*
920                          * Most pages have a mapping and most filesystems
921                          * provide a migratepage callback. Anonymous pages
922                          * are part of swap space which also has its own
923                          * migratepage callback. This is the most common path
924                          * for page migration.
925                          */
926                         rc = mapping->a_ops->migratepage(mapping, newpage,
927                                                         page, mode);
928                 else
929                         rc = fallback_migrate_page(mapping, newpage,
930                                                         page, mode);
931         } else {
932                 /*
933                  * In case of non-lru page, it could be released after
934                  * isolation step. In that case, we shouldn't try migration.
935                  */
936                 VM_BUG_ON_PAGE(!PageIsolated(page), page);
937                 if (!PageMovable(page)) {
938                         rc = MIGRATEPAGE_SUCCESS;
939                         __ClearPageIsolated(page);
940                         goto out;
941                 }
942 
943                 rc = mapping->a_ops->migratepage(mapping, newpage,
944                                                 page, mode);
945                 WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS &&
946                         !PageIsolated(page));
947         }
948 
949         /*
950          * When successful, old pagecache page->mapping must be cleared before
951          * page is freed; but stats require that PageAnon be left as PageAnon.
952          */
953         if (rc == MIGRATEPAGE_SUCCESS) {
954                 if (__PageMovable(page)) {
955                         VM_BUG_ON_PAGE(!PageIsolated(page), page);
956 
957                         /*
958                          * We clear PG_movable under page_lock so any compactor
959                          * cannot try to migrate this page.
960                          */
961                         __ClearPageIsolated(page);
962                 }
963 
964                 /*
965                  * Anonymous and movable page->mapping will be cleard by
966                  * free_pages_prepare so don't reset it here for keeping
967                  * the type to work PageAnon, for example.
968                  */
969                 if (!PageMappingFlags(page))
970                         page->mapping = NULL;
971         }
972 out:
973         return rc;
974 }
975 
976 static int __unmap_and_move(struct page *page, struct page *newpage,
977                                 int force, enum migrate_mode mode)
978 {
979         int rc = -EAGAIN;
980         int page_was_mapped = 0;
981         struct anon_vma *anon_vma = NULL;
982         bool is_lru = !__PageMovable(page);
983 
984         if (!trylock_page(page)) {
985                 if (!force || mode == MIGRATE_ASYNC)
986                         goto out;
987 
988                 /*
989                  * It's not safe for direct compaction to call lock_page.
990                  * For example, during page readahead pages are added locked
991                  * to the LRU. Later, when the IO completes the pages are
992                  * marked uptodate and unlocked. However, the queueing
993                  * could be merging multiple pages for one bio (e.g.
994                  * mpage_readpages). If an allocation happens for the
995                  * second or third page, the process can end up locking
996                  * the same page twice and deadlocking. Rather than
997                  * trying to be clever about what pages can be locked,
998                  * avoid the use of lock_page for direct compaction
999                  * altogether.
1000                  */
1001                 if (current->flags & PF_MEMALLOC)
1002                         goto out;
1003 
1004                 lock_page(page);
1005         }
1006 
1007         if (PageWriteback(page)) {
1008                 /*
1009                  * Only in the case of a full synchronous migration is it
1010                  * necessary to wait for PageWriteback. In the async case,
1011                  * the retry loop is too short and in the sync-light case,
1012                  * the overhead of stalling is too much
1013                  */
1014                 switch (mode) {
1015                 case MIGRATE_SYNC:
1016                 case MIGRATE_SYNC_NO_COPY:
1017                         break;
1018                 default:
1019                         rc = -EBUSY;
1020                         goto out_unlock;
1021                 }
1022                 if (!force)
1023                         goto out_unlock;
1024                 wait_on_page_writeback(page);
1025         }
1026 
1027         /*
1028          * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
1029          * we cannot notice that anon_vma is freed while we migrates a page.
1030          * This get_anon_vma() delays freeing anon_vma pointer until the end
1031          * of migration. File cache pages are no problem because of page_lock()
1032          * File Caches may use write_page() or lock_page() in migration, then,
1033          * just care Anon page here.
1034          *
1035          * Only page_get_anon_vma() understands the subtleties of
1036          * getting a hold on an anon_vma from outside one of its mms.
1037          * But if we cannot get anon_vma, then we won't need it anyway,
1038          * because that implies that the anon page is no longer mapped
1039          * (and cannot be remapped so long as we hold the page lock).
1040          */
1041         if (PageAnon(page) && !PageKsm(page))
1042                 anon_vma = page_get_anon_vma(page);
1043 
1044         /*
1045          * Block others from accessing the new page when we get around to
1046          * establishing additional references. We are usually the only one
1047          * holding a reference to newpage at this point. We used to have a BUG
1048          * here if trylock_page(newpage) fails, but would like to allow for
1049          * cases where there might be a race with the previous use of newpage.
1050          * This is much like races on refcount of oldpage: just don't BUG().
1051          */
1052         if (unlikely(!trylock_page(newpage)))
1053                 goto out_unlock;
1054 
1055         if (unlikely(!is_lru)) {
1056                 rc = move_to_new_page(newpage, page, mode);
1057                 goto out_unlock_both;
1058         }
1059 
1060         /*
1061          * Corner case handling:
1062          * 1. When a new swap-cache page is read into, it is added to the LRU
1063          * and treated as swapcache but it has no rmap yet.
1064          * Calling try_to_unmap() against a page->mapping==NULL page will
1065          * trigger a BUG.  So handle it here.
1066          * 2. An orphaned page (see truncate_complete_page) might have
1067          * fs-private metadata. The page can be picked up due to memory
1068          * offlining.  Everywhere else except page reclaim, the page is
1069          * invisible to the vm, so the page can not be migrated.  So try to
1070          * free the metadata, so the page can be freed.
1071          */
1072         if (!page->mapping) {
1073                 VM_BUG_ON_PAGE(PageAnon(page), page);
1074                 if (page_has_private(page)) {
1075                         try_to_free_buffers(page);
1076                         goto out_unlock_both;
1077                 }
1078         } else if (page_mapped(page)) {
1079                 /* Establish migration ptes */
1080                 VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma,
1081                                 page);
1082                 try_to_unmap(page,
1083                         TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
1084                 page_was_mapped = 1;
1085         }
1086 
1087         if (!page_mapped(page))
1088                 rc = move_to_new_page(newpage, page, mode);
1089 
1090         if (page_was_mapped)
1091                 remove_migration_ptes(page,
1092                         rc == MIGRATEPAGE_SUCCESS ? newpage : page, false);
1093 
1094 out_unlock_both:
1095         unlock_page(newpage);
1096 out_unlock:
1097         /* Drop an anon_vma reference if we took one */
1098         if (anon_vma)
1099                 put_anon_vma(anon_vma);
1100         unlock_page(page);
1101 out:
1102         /*
1103          * If migration is successful, decrease refcount of the newpage
1104          * which will not free the page because new page owner increased
1105          * refcounter. As well, if it is LRU page, add the page to LRU
1106          * list in here.
1107          */
1108         if (rc == MIGRATEPAGE_SUCCESS) {
1109                 if (unlikely(__PageMovable(newpage)))
1110                         put_page(newpage);
1111                 else
1112                         putback_lru_page(newpage);
1113         }
1114 
1115         return rc;
1116 }
1117 
1118 /*
1119  * gcc 4.7 and 4.8 on arm get an ICEs when inlining unmap_and_move().  Work
1120  * around it.
1121  */
1122 #if (GCC_VERSION >= 40700 && GCC_VERSION < 40900) && defined(CONFIG_ARM)
1123 #define ICE_noinline noinline
1124 #else
1125 #define ICE_noinline
1126 #endif
1127 
1128 /*
1129  * Obtain the lock on page, remove all ptes and migrate the page
1130  * to the newly allocated page in newpage.
1131  */
1132 static ICE_noinline int unmap_and_move(new_page_t get_new_page,
1133                                    free_page_t put_new_page,
1134                                    unsigned long private, struct page *page,
1135                                    int force, enum migrate_mode mode,
1136                                    enum migrate_reason reason)
1137 {
1138         int rc = MIGRATEPAGE_SUCCESS;
1139         int *result = NULL;
1140         struct page *newpage;
1141 
1142         newpage = get_new_page(page, private, &result);
1143         if (!newpage)
1144                 return -ENOMEM;
1145 
1146         if (page_count(page) == 1) {
1147                 /* page was freed from under us. So we are done. */
1148                 ClearPageActive(page);
1149                 ClearPageUnevictable(page);
1150                 if (unlikely(__PageMovable(page))) {
1151                         lock_page(page);
1152                         if (!PageMovable(page))
1153                                 __ClearPageIsolated(page);
1154                         unlock_page(page);
1155                 }
1156                 if (put_new_page)
1157                         put_new_page(newpage, private);
1158                 else
1159                         put_page(newpage);
1160                 goto out;
1161         }
1162 
1163         if (unlikely(PageTransHuge(page) && !PageTransHuge(newpage))) {
1164                 lock_page(page);
1165                 rc = split_huge_page(page);
1166                 unlock_page(page);
1167                 if (rc)
1168                         goto out;
1169         }
1170 
1171         rc = __unmap_and_move(page, newpage, force, mode);
1172         if (rc == MIGRATEPAGE_SUCCESS)
1173                 set_page_owner_migrate_reason(newpage, reason);
1174 
1175 out:
1176         if (rc != -EAGAIN) {
1177                 /*
1178                  * A page that has been migrated has all references
1179                  * removed and will be freed. A page that has not been
1180                  * migrated will have kepts its references and be
1181                  * restored.
1182                  */
1183                 list_del(&page->lru);
1184 
1185                 /*
1186                  * Compaction can migrate also non-LRU pages which are
1187                  * not accounted to NR_ISOLATED_*. They can be recognized
1188                  * as __PageMovable
1189                  */
1190                 if (likely(!__PageMovable(page)))
1191                         mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON +
1192                                         page_is_file_cache(page), -hpage_nr_pages(page));
1193         }
1194 
1195         /*
1196          * If migration is successful, releases reference grabbed during
1197          * isolation. Otherwise, restore the page to right list unless
1198          * we want to retry.
1199          */
1200         if (rc == MIGRATEPAGE_SUCCESS) {
1201                 put_page(page);
1202                 if (reason == MR_MEMORY_FAILURE) {
1203                         /*
1204                          * Set PG_HWPoison on just freed page
1205                          * intentionally. Although it's rather weird,
1206                          * it's how HWPoison flag works at the moment.
1207                          */
1208                         if (!test_set_page_hwpoison(page))
1209                                 num_poisoned_pages_inc();
1210                 }
1211         } else {
1212                 if (rc != -EAGAIN) {
1213                         if (likely(!__PageMovable(page))) {
1214                                 putback_lru_page(page);
1215                                 goto put_new;
1216                         }
1217 
1218                         lock_page(page);
1219                         if (PageMovable(page))
1220                                 putback_movable_page(page);
1221                         else
1222                                 __ClearPageIsolated(page);
1223                         unlock_page(page);
1224                         put_page(page);
1225                 }
1226 put_new:
1227                 if (put_new_page)
1228                         put_new_page(newpage, private);
1229                 else
1230                         put_page(newpage);
1231         }
1232 
1233         if (result) {
1234                 if (rc)
1235                         *result = rc;
1236                 else
1237                         *result = page_to_nid(newpage);
1238         }
1239         return rc;
1240 }
1241 
1242 /*
1243  * Counterpart of unmap_and_move_page() for hugepage migration.
1244  *
1245  * This function doesn't wait the completion of hugepage I/O
1246  * because there is no race between I/O and migration for hugepage.
1247  * Note that currently hugepage I/O occurs only in direct I/O
1248  * where no lock is held and PG_writeback is irrelevant,
1249  * and writeback status of all subpages are counted in the reference
1250  * count of the head page (i.e. if all subpages of a 2MB hugepage are
1251  * under direct I/O, the reference of the head page is 512 and a bit more.)
1252  * This means that when we try to migrate hugepage whose subpages are
1253  * doing direct I/O, some references remain after try_to_unmap() and
1254  * hugepage migration fails without data corruption.
1255  *
1256  * There is also no race when direct I/O is issued on the page under migration,
1257  * because then pte is replaced with migration swap entry and direct I/O code
1258  * will wait in the page fault for migration to complete.
1259  */
1260 static int unmap_and_move_huge_page(new_page_t get_new_page,
1261                                 free_page_t put_new_page, unsigned long private,
1262                                 struct page *hpage, int force,
1263                                 enum migrate_mode mode, int reason)
1264 {
1265         int rc = -EAGAIN;
1266         int *result = NULL;
1267         int page_was_mapped = 0;
1268         struct page *new_hpage;
1269         struct anon_vma *anon_vma = NULL;
1270 
1271         /*
1272          * Movability of hugepages depends on architectures and hugepage size.
1273          * This check is necessary because some callers of hugepage migration
1274          * like soft offline and memory hotremove don't walk through page
1275          * tables or check whether the hugepage is pmd-based or not before
1276          * kicking migration.
1277          */
1278         if (!hugepage_migration_supported(page_hstate(hpage))) {
1279                 putback_active_hugepage(hpage);
1280                 return -ENOSYS;
1281         }
1282 
1283         new_hpage = get_new_page(hpage, private, &result);
1284         if (!new_hpage)
1285                 return -ENOMEM;
1286 
1287         if (!trylock_page(hpage)) {
1288                 if (!force)
1289                         goto out;
1290                 switch (mode) {
1291                 case MIGRATE_SYNC:
1292                 case MIGRATE_SYNC_NO_COPY:
1293                         break;
1294                 default:
1295                         goto out;
1296                 }
1297                 lock_page(hpage);
1298         }
1299 
1300         if (PageAnon(hpage))
1301                 anon_vma = page_get_anon_vma(hpage);
1302 
1303         if (unlikely(!trylock_page(new_hpage)))
1304                 goto put_anon;
1305 
1306         if (page_mapped(hpage)) {
1307                 try_to_unmap(hpage,
1308                         TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
1309                 page_was_mapped = 1;
1310         }
1311 
1312         if (!page_mapped(hpage))
1313                 rc = move_to_new_page(new_hpage, hpage, mode);
1314 
1315         if (page_was_mapped)
1316                 remove_migration_ptes(hpage,
1317                         rc == MIGRATEPAGE_SUCCESS ? new_hpage : hpage, false);
1318 
1319         unlock_page(new_hpage);
1320 
1321 put_anon:
1322         if (anon_vma)
1323                 put_anon_vma(anon_vma);
1324 
1325         if (rc == MIGRATEPAGE_SUCCESS) {
1326                 hugetlb_cgroup_migrate(hpage, new_hpage);
1327                 put_new_page = NULL;
1328                 set_page_owner_migrate_reason(new_hpage, reason);
1329         }
1330 
1331         unlock_page(hpage);
1332 out:
1333         if (rc != -EAGAIN)
1334                 putback_active_hugepage(hpage);
1335         if (reason == MR_MEMORY_FAILURE && !test_set_page_hwpoison(hpage))
1336                 num_poisoned_pages_inc();
1337 
1338         /*
1339          * If migration was not successful and there's a freeing callback, use
1340          * it.  Otherwise, put_page() will drop the reference grabbed during
1341          * isolation.
1342          */
1343         if (put_new_page)
1344                 put_new_page(new_hpage, private);
1345         else
1346                 putback_active_hugepage(new_hpage);
1347 
1348         if (result) {
1349                 if (rc)
1350                         *result = rc;
1351                 else
1352                         *result = page_to_nid(new_hpage);
1353         }
1354         return rc;
1355 }
1356 
1357 /*
1358  * migrate_pages - migrate the pages specified in a list, to the free pages
1359  *                 supplied as the target for the page migration
1360  *
1361  * @from:               The list of pages to be migrated.
1362  * @get_new_page:       The function used to allocate free pages to be used
1363  *                      as the target of the page migration.
1364  * @put_new_page:       The function used to free target pages if migration
1365  *                      fails, or NULL if no special handling is necessary.
1366  * @private:            Private data to be passed on to get_new_page()
1367  * @mode:               The migration mode that specifies the constraints for
1368  *                      page migration, if any.
1369  * @reason:             The reason for page migration.
1370  *
1371  * The function returns after 10 attempts or if no pages are movable any more
1372  * because the list has become empty or no retryable pages exist any more.
1373  * The caller should call putback_movable_pages() to return pages to the LRU
1374  * or free list only if ret != 0.
1375  *
1376  * Returns the number of pages that were not migrated, or an error code.
1377  */
1378 int migrate_pages(struct list_head *from, new_page_t get_new_page,
1379                 free_page_t put_new_page, unsigned long private,
1380                 enum migrate_mode mode, int reason)
1381 {
1382         int retry = 1;
1383         int nr_failed = 0;
1384         int nr_succeeded = 0;
1385         int pass = 0;
1386         struct page *page;
1387         struct page *page2;
1388         int swapwrite = current->flags & PF_SWAPWRITE;
1389         int rc;
1390 
1391         if (!swapwrite)
1392                 current->flags |= PF_SWAPWRITE;
1393 
1394         for(pass = 0; pass < 10 && retry; pass++) {
1395                 retry = 0;
1396 
1397                 list_for_each_entry_safe(page, page2, from, lru) {
1398                         cond_resched();
1399 
1400                         if (PageHuge(page))
1401                                 rc = unmap_and_move_huge_page(get_new_page,
1402                                                 put_new_page, private, page,
1403                                                 pass > 2, mode, reason);
1404                         else
1405                                 rc = unmap_and_move(get_new_page, put_new_page,
1406                                                 private, page, pass > 2, mode,
1407                                                 reason);
1408 
1409                         switch(rc) {
1410                         case -ENOMEM:
1411                                 nr_failed++;
1412                                 goto out;
1413                         case -EAGAIN:
1414                                 retry++;
1415                                 break;
1416                         case MIGRATEPAGE_SUCCESS:
1417                                 nr_succeeded++;
1418                                 break;
1419                         default:
1420                                 /*
1421                                  * Permanent failure (-EBUSY, -ENOSYS, etc.):
1422                                  * unlike -EAGAIN case, the failed page is
1423                                  * removed from migration page list and not
1424                                  * retried in the next outer loop.
1425                                  */
1426                                 nr_failed++;
1427                                 break;
1428                         }
1429                 }
1430         }
1431         nr_failed += retry;
1432         rc = nr_failed;
1433 out:
1434         if (nr_succeeded)
1435                 count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
1436         if (nr_failed)
1437                 count_vm_events(PGMIGRATE_FAIL, nr_failed);
1438         trace_mm_migrate_pages(nr_succeeded, nr_failed, mode, reason);
1439 
1440         if (!swapwrite)
1441                 current->flags &= ~PF_SWAPWRITE;
1442 
1443         return rc;
1444 }
1445 
1446 #ifdef CONFIG_NUMA
1447 /*
1448  * Move a list of individual pages
1449  */
1450 struct page_to_node {
1451         unsigned long addr;
1452         struct page *page;
1453         int node;
1454         int status;
1455 };
1456 
1457 static struct page *new_page_node(struct page *p, unsigned long private,
1458                 int **result)
1459 {
1460         struct page_to_node *pm = (struct page_to_node *)private;
1461 
1462         while (pm->node != MAX_NUMNODES && pm->page != p)
1463                 pm++;
1464 
1465         if (pm->node == MAX_NUMNODES)
1466                 return NULL;
1467 
1468         *result = &pm->status;
1469 
1470         if (PageHuge(p))
1471                 return alloc_huge_page_node(page_hstate(compound_head(p)),
1472                                         pm->node);
1473         else if (thp_migration_supported() && PageTransHuge(p)) {
1474                 struct page *thp;
1475 
1476                 thp = alloc_pages_node(pm->node,
1477                         (GFP_TRANSHUGE | __GFP_THISNODE) & ~__GFP_RECLAIM,
1478                         HPAGE_PMD_ORDER);
1479                 if (!thp)
1480                         return NULL;
1481                 prep_transhuge_page(thp);
1482                 return thp;
1483         } else
1484                 return __alloc_pages_node(pm->node,
1485                                 GFP_HIGHUSER_MOVABLE | __GFP_THISNODE, 0);
1486 }
1487 
1488 /*
1489  * Move a set of pages as indicated in the pm array. The addr
1490  * field must be set to the virtual address of the page to be moved
1491  * and the node number must contain a valid target node.
1492  * The pm array ends with node = MAX_NUMNODES.
1493  */
1494 static int do_move_page_to_node_array(struct mm_struct *mm,
1495                                       struct page_to_node *pm,
1496                                       int migrate_all)
1497 {
1498         int err;
1499         struct page_to_node *pp;
1500         LIST_HEAD(pagelist);
1501 
1502         down_read(&mm->mmap_sem);
1503 
1504         /*
1505          * Build a list of pages to migrate
1506          */
1507         for (pp = pm; pp->node != MAX_NUMNODES; pp++) {
1508                 struct vm_area_struct *vma;
1509                 struct page *page;
1510                 struct page *head;
1511                 unsigned int follflags;
1512 
1513                 err = -EFAULT;
1514                 vma = find_vma(mm, pp->addr);
1515                 if (!vma || pp->addr < vma->vm_start || !vma_migratable(vma))
1516                         goto set_status;
1517 
1518                 /* FOLL_DUMP to ignore special (like zero) pages */
1519                 follflags = FOLL_GET | FOLL_DUMP;
1520                 if (!thp_migration_supported())
1521                         follflags |= FOLL_SPLIT;
1522                 page = follow_page(vma, pp->addr, follflags);
1523 
1524                 err = PTR_ERR(page);
1525                 if (IS_ERR(page))
1526                         goto set_status;
1527 
1528                 err = -ENOENT;
1529                 if (!page)
1530                         goto set_status;
1531 
1532                 err = page_to_nid(page);
1533 
1534                 if (err == pp->node)
1535                         /*
1536                          * Node already in the right place
1537                          */
1538                         goto put_and_set;
1539 
1540                 err = -EACCES;
1541                 if (page_mapcount(page) > 1 &&
1542                                 !migrate_all)
1543                         goto put_and_set;
1544 
1545                 if (PageHuge(page)) {
1546                         if (PageHead(page)) {
1547                                 isolate_huge_page(page, &pagelist);
1548                                 err = 0;
1549                                 pp->page = page;
1550                         }
1551                         goto put_and_set;
1552                 }
1553 
1554                 pp->page = compound_head(page);
1555                 head = compound_head(page);
1556                 err = isolate_lru_page(head);
1557                 if (!err) {
1558                         list_add_tail(&head->lru, &pagelist);
1559                         mod_node_page_state(page_pgdat(head),
1560                                 NR_ISOLATED_ANON + page_is_file_cache(head),
1561                                 hpage_nr_pages(head));
1562                 }
1563 put_and_set:
1564                 /*
1565                  * Either remove the duplicate refcount from
1566                  * isolate_lru_page() or drop the page ref if it was
1567                  * not isolated.
1568                  */
1569                 put_page(page);
1570 set_status:
1571                 pp->status = err;
1572         }
1573 
1574         err = 0;
1575         if (!list_empty(&pagelist)) {
1576                 err = migrate_pages(&pagelist, new_page_node, NULL,
1577                                 (unsigned long)pm, MIGRATE_SYNC, MR_SYSCALL);
1578                 if (err)
1579                         putback_movable_pages(&pagelist);
1580         }
1581 
1582         up_read(&mm->mmap_sem);
1583         return err;
1584 }
1585 
1586 /*
1587  * Migrate an array of page address onto an array of nodes and fill
1588  * the corresponding array of status.
1589  */
1590 static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
1591                          unsigned long nr_pages,
1592                          const void __user * __user *pages,
1593                          const int __user *nodes,
1594                          int __user *status, int flags)
1595 {
1596         struct page_to_node *pm;
1597         unsigned long chunk_nr_pages;
1598         unsigned long chunk_start;
1599         int err;
1600 
1601         err = -ENOMEM;
1602         pm = (struct page_to_node *)__get_free_page(GFP_KERNEL);
1603         if (!pm)
1604                 goto out;
1605 
1606         migrate_prep();
1607 
1608         /*
1609          * Store a chunk of page_to_node array in a page,
1610          * but keep the last one as a marker
1611          */
1612         chunk_nr_pages = (PAGE_SIZE / sizeof(struct page_to_node)) - 1;
1613 
1614         for (chunk_start = 0;
1615              chunk_start < nr_pages;
1616              chunk_start += chunk_nr_pages) {
1617                 int j;
1618 
1619                 if (chunk_start + chunk_nr_pages > nr_pages)
1620                         chunk_nr_pages = nr_pages - chunk_start;
1621 
1622                 /* fill the chunk pm with addrs and nodes from user-space */
1623                 for (j = 0; j < chunk_nr_pages; j++) {
1624                         const void __user *p;
1625                         int node;
1626 
1627                         err = -EFAULT;
1628                         if (get_user(p, pages + j + chunk_start))
1629                                 goto out_pm;
1630                         pm[j].addr = (unsigned long) p;
1631 
1632                         if (get_user(node, nodes + j + chunk_start))
1633                                 goto out_pm;
1634 
1635                         err = -ENODEV;
1636                         if (node < 0 || node >= MAX_NUMNODES)
1637                                 goto out_pm;
1638 
1639                         if (!node_state(node, N_MEMORY))
1640                                 goto out_pm;
1641 
1642                         err = -EACCES;
1643                         if (!node_isset(node, task_nodes))
1644                                 goto out_pm;
1645 
1646                         pm[j].node = node;
1647                 }
1648 
1649                 /* End marker for this chunk */
1650                 pm[chunk_nr_pages].node = MAX_NUMNODES;
1651 
1652                 /* Migrate this chunk */
1653                 err = do_move_page_to_node_array(mm, pm,
1654                                                  flags & MPOL_MF_MOVE_ALL);
1655                 if (err < 0)
1656                         goto out_pm;
1657 
1658                 /* Return status information */
1659                 for (j = 0; j < chunk_nr_pages; j++)
1660                         if (put_user(pm[j].status, status + j + chunk_start)) {
1661                                 err = -EFAULT;
1662                                 goto out_pm;
1663                         }
1664         }
1665         err = 0;
1666 
1667 out_pm:
1668         free_page((unsigned long)pm);
1669 out:
1670         return err;
1671 }
1672 
1673 /*
1674  * Determine the nodes of an array of pages and store it in an array of status.
1675  */
1676 static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
1677                                 const void __user **pages, int *status)
1678 {
1679         unsigned long i;
1680 
1681         down_read(&mm->mmap_sem);
1682 
1683         for (i = 0; i < nr_pages; i++) {
1684                 unsigned long addr = (unsigned long)(*pages);
1685                 struct vm_area_struct *vma;
1686                 struct page *page;
1687                 int err = -EFAULT;
1688 
1689                 vma = find_vma(mm, addr);
1690                 if (!vma || addr < vma->vm_start)
1691                         goto set_status;
1692 
1693                 /* FOLL_DUMP to ignore special (like zero) pages */
1694                 page = follow_page(vma, addr, FOLL_DUMP);
1695 
1696                 err = PTR_ERR(page);
1697                 if (IS_ERR(page))
1698                         goto set_status;
1699 
1700                 err = page ? page_to_nid(page) : -ENOENT;
1701 set_status:
1702                 *status = err;
1703 
1704                 pages++;
1705                 status++;
1706         }
1707 
1708         up_read(&mm->mmap_sem);
1709 }
1710 
1711 /*
1712  * Determine the nodes of a user array of pages and store it in
1713  * a user array of status.
1714  */
1715 static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
1716                          const void __user * __user *pages,
1717                          int __user *status)
1718 {
1719 #define DO_PAGES_STAT_CHUNK_NR 16
1720         const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
1721         int chunk_status[DO_PAGES_STAT_CHUNK_NR];
1722 
1723         while (nr_pages) {
1724                 unsigned long chunk_nr;
1725 
1726                 chunk_nr = nr_pages;
1727                 if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
1728                         chunk_nr = DO_PAGES_STAT_CHUNK_NR;
1729 
1730                 if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages)))
1731                         break;
1732 
1733                 do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
1734 
1735                 if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
1736                         break;
1737 
1738                 pages += chunk_nr;
1739                 status += chunk_nr;
1740                 nr_pages -= chunk_nr;
1741         }
1742         return nr_pages ? -EFAULT : 0;
1743 }
1744 
1745 /*
1746  * Move a list of pages in the address space of the currently executing
1747  * process.
1748  */
1749 SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
1750                 const void __user * __user *, pages,
1751                 const int __user *, nodes,
1752                 int __user *, status, int, flags)
1753 {
1754         struct task_struct *task;
1755         struct mm_struct *mm;
1756         int err;
1757         nodemask_t task_nodes;
1758 
1759         /* Check flags */
1760         if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
1761                 return -EINVAL;
1762 
1763         if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
1764                 return -EPERM;
1765 
1766         /* Find the mm_struct */
1767         rcu_read_lock();
1768         task = pid ? find_task_by_vpid(pid) : current;
1769         if (!task) {
1770                 rcu_read_unlock();
1771                 return -ESRCH;
1772         }
1773         get_task_struct(task);
1774 
1775         /*
1776          * Check if this process has the right to modify the specified
1777          * process. Use the regular "ptrace_may_access()" checks.
1778          */
1779         if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) {
1780                 rcu_read_unlock();
1781                 err = -EPERM;
1782                 goto out;
1783         }
1784         rcu_read_unlock();
1785 
1786         err = security_task_movememory(task);
1787         if (err)
1788                 goto out;
1789 
1790         task_nodes = cpuset_mems_allowed(task);
1791         mm = get_task_mm(task);
1792         put_task_struct(task);
1793 
1794         if (!mm)
1795                 return -EINVAL;
1796 
1797         if (nodes)
1798                 err = do_pages_move(mm, task_nodes, nr_pages, pages,
1799                                     nodes, status, flags);
1800         else
1801                 err = do_pages_stat(mm, nr_pages, pages, status);
1802 
1803         mmput(mm);
1804         return err;
1805 
1806 out:
1807         put_task_struct(task);
1808         return err;
1809 }
1810 
1811 #ifdef CONFIG_NUMA_BALANCING
1812 /*
1813  * Returns true if this is a safe migration target node for misplaced NUMA
1814  * pages. Currently it only checks the watermarks which crude
1815  */
1816 static bool migrate_balanced_pgdat(struct pglist_data *pgdat,
1817                                    unsigned long nr_migrate_pages)
1818 {
1819         int z;
1820 
1821         for (z = pgdat->nr_zones - 1; z >= 0; z--) {
1822                 struct zone *zone = pgdat->node_zones + z;
1823 
1824                 if (!populated_zone(zone))
1825                         continue;
1826 
1827                 /* Avoid waking kswapd by allocating pages_to_migrate pages. */
1828                 if (!zone_watermark_ok(zone, 0,
1829                                        high_wmark_pages(zone) +
1830                                        nr_migrate_pages,
1831                                        0, 0))
1832                         continue;
1833                 return true;
1834         }
1835         return false;
1836 }
1837 
1838 static struct page *alloc_misplaced_dst_page(struct page *page,
1839                                            unsigned long data,
1840                                            int **result)
1841 {
1842         int nid = (int) data;
1843         struct page *newpage;
1844 
1845         newpage = __alloc_pages_node(nid,
1846                                          (GFP_HIGHUSER_MOVABLE |
1847                                           __GFP_THISNODE | __GFP_NOMEMALLOC |
1848                                           __GFP_NORETRY | __GFP_NOWARN) &
1849                                          ~__GFP_RECLAIM, 0);
1850 
1851         return newpage;
1852 }
1853 
1854 /*
1855  * page migration rate limiting control.
1856  * Do not migrate more than @pages_to_migrate in a @migrate_interval_millisecs
1857  * window of time. Default here says do not migrate more than 1280M per second.
1858  */
1859 static unsigned int migrate_interval_millisecs __read_mostly = 100;
1860 static unsigned int ratelimit_pages __read_mostly = 128 << (20 - PAGE_SHIFT);
1861 
1862 /* Returns true if the node is migrate rate-limited after the update */
1863 static bool numamigrate_update_ratelimit(pg_data_t *pgdat,
1864                                         unsigned long nr_pages)
1865 {
1866         /*
1867          * Rate-limit the amount of data that is being migrated to a node.
1868          * Optimal placement is no good if the memory bus is saturated and
1869          * all the time is being spent migrating!
1870          */
1871         if (time_after(jiffies, pgdat->numabalancing_migrate_next_window)) {
1872                 spin_lock(&pgdat->numabalancing_migrate_lock);
1873                 pgdat->numabalancing_migrate_nr_pages = 0;
1874                 pgdat->numabalancing_migrate_next_window = jiffies +
1875                         msecs_to_jiffies(migrate_interval_millisecs);
1876                 spin_unlock(&pgdat->numabalancing_migrate_lock);
1877         }
1878         if (pgdat->numabalancing_migrate_nr_pages > ratelimit_pages) {
1879                 trace_mm_numa_migrate_ratelimit(current, pgdat->node_id,
1880                                                                 nr_pages);
1881                 return true;
1882         }
1883 
1884         /*
1885          * This is an unlocked non-atomic update so errors are possible.
1886          * The consequences are failing to migrate when we potentiall should
1887          * have which is not severe enough to warrant locking. If it is ever
1888          * a problem, it can be converted to a per-cpu counter.
1889          */
1890         pgdat->numabalancing_migrate_nr_pages += nr_pages;
1891         return false;
1892 }
1893 
1894 static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
1895 {
1896         int page_lru;
1897 
1898         VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page);
1899 
1900         /* Avoid migrating to a node that is nearly full */
1901         if (!migrate_balanced_pgdat(pgdat, 1UL << compound_order(page)))
1902                 return 0;
1903 
1904         if (isolate_lru_page(page))
1905                 return 0;
1906 
1907         /*
1908          * migrate_misplaced_transhuge_page() skips page migration's usual
1909          * check on page_count(), so we must do it here, now that the page
1910          * has been isolated: a GUP pin, or any other pin, prevents migration.
1911          * The expected page count is 3: 1 for page's mapcount and 1 for the
1912          * caller's pin and 1 for the reference taken by isolate_lru_page().
1913          */
1914         if (PageTransHuge(page) && page_count(page) != 3) {
1915                 putback_lru_page(page);
1916                 return 0;
1917         }
1918 
1919         page_lru = page_is_file_cache(page);
1920         mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + page_lru,
1921                                 hpage_nr_pages(page));
1922 
1923         /*
1924          * Isolating the page has taken another reference, so the
1925          * caller's reference can be safely dropped without the page
1926          * disappearing underneath us during migration.
1927          */
1928         put_page(page);
1929         return 1;
1930 }
1931 
1932 bool pmd_trans_migrating(pmd_t pmd)
1933 {
1934         struct page *page = pmd_page(pmd);
1935         return PageLocked(page);
1936 }
1937 
1938 /*
1939  * Attempt to migrate a misplaced page to the specified destination
1940  * node. Caller is expected to have an elevated reference count on
1941  * the page that will be dropped by this function before returning.
1942  */
1943 int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
1944                            int node)
1945 {
1946         pg_data_t *pgdat = NODE_DATA(node);
1947         int isolated;
1948         int nr_remaining;
1949         LIST_HEAD(migratepages);
1950 
1951         /*
1952          * Don't migrate file pages that are mapped in multiple processes
1953          * with execute permissions as they are probably shared libraries.
1954          */
1955         if (page_mapcount(page) != 1 && page_is_file_cache(page) &&
1956             (vma->vm_flags & VM_EXEC))
1957                 goto out;
1958 
1959         /*
1960          * Rate-limit the amount of data that is being migrated to a node.
1961          * Optimal placement is no good if the memory bus is saturated and
1962          * all the time is being spent migrating!
1963          */
1964         if (numamigrate_update_ratelimit(pgdat, 1))
1965                 goto out;
1966 
1967         isolated = numamigrate_isolate_page(pgdat, page);
1968         if (!isolated)
1969                 goto out;
1970 
1971         list_add(&page->lru, &migratepages);
1972         nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_page,
1973                                      NULL, node, MIGRATE_ASYNC,
1974                                      MR_NUMA_MISPLACED);
1975         if (nr_remaining) {
1976                 if (!list_empty(&migratepages)) {
1977                         list_del(&page->lru);
1978                         dec_node_page_state(page, NR_ISOLATED_ANON +
1979                                         page_is_file_cache(page));
1980                         putback_lru_page(page);
1981                 }
1982                 isolated = 0;
1983         } else
1984                 count_vm_numa_event(NUMA_PAGE_MIGRATE);
1985         BUG_ON(!list_empty(&migratepages));
1986         return isolated;
1987 
1988 out:
1989         put_page(page);
1990         return 0;
1991 }
1992 #endif /* CONFIG_NUMA_BALANCING */
1993 
1994 #if defined(CONFIG_NUMA_BALANCING) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
1995 /*
1996  * Migrates a THP to a given target node. page must be locked and is unlocked
1997  * before returning.
1998  */
1999 int migrate_misplaced_transhuge_page(struct mm_struct *mm,
2000                                 struct vm_area_struct *vma,
2001                                 pmd_t *pmd, pmd_t entry,
2002                                 unsigned long address,
2003                                 struct page *page, int node)
2004 {
2005         spinlock_t *ptl;
2006         pg_data_t *pgdat = NODE_DATA(node);
2007         int isolated = 0;
2008         struct page *new_page = NULL;
2009         int page_lru = page_is_file_cache(page);
2010         unsigned long mmun_start = address & HPAGE_PMD_MASK;
2011         unsigned long mmun_end = mmun_start + HPAGE_PMD_SIZE;
2012 
2013         /*
2014          * Rate-limit the amount of data that is being migrated to a node.
2015          * Optimal placement is no good if the memory bus is saturated and
2016          * all the time is being spent migrating!
2017          */
2018         if (numamigrate_update_ratelimit(pgdat, HPAGE_PMD_NR))
2019                 goto out_dropref;
2020 
2021         new_page = alloc_pages_node(node,
2022                 (GFP_TRANSHUGE_LIGHT | __GFP_THISNODE),
2023                 HPAGE_PMD_ORDER);
2024         if (!new_page)
2025                 goto out_fail;
2026         prep_transhuge_page(new_page);
2027 
2028         isolated = numamigrate_isolate_page(pgdat, page);
2029         if (!isolated) {
2030                 put_page(new_page);
2031                 goto out_fail;
2032         }
2033 
2034         /* Prepare a page as a migration target */
2035         __SetPageLocked(new_page);
2036         if (PageSwapBacked(page))
2037                 __SetPageSwapBacked(new_page);
2038 
2039         /* anon mapping, we can simply copy page->mapping to the new page: */
2040         new_page->mapping = page->mapping;
2041         new_page->index = page->index;
2042         migrate_page_copy(new_page, page);
2043         WARN_ON(PageLRU(new_page));
2044 
2045         /* Recheck the target PMD */
2046         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2047         ptl = pmd_lock(mm, pmd);
2048         if (unlikely(!pmd_same(*pmd, entry) || !page_ref_freeze(page, 2))) {
2049                 spin_unlock(ptl);
2050                 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2051 
2052                 /* Reverse changes made by migrate_page_copy() */
2053                 if (TestClearPageActive(new_page))
2054                         SetPageActive(page);
2055                 if (TestClearPageUnevictable(new_page))
2056                         SetPageUnevictable(page);
2057 
2058                 unlock_page(new_page);
2059                 put_page(new_page);             /* Free it */
2060 
2061                 /* Retake the callers reference and putback on LRU */
2062                 get_page(page);
2063                 putback_lru_page(page);
2064                 mod_node_page_state(page_pgdat(page),
2065                          NR_ISOLATED_ANON + page_lru, -HPAGE_PMD_NR);
2066 
2067                 goto out_unlock;
2068         }
2069 
2070         entry = mk_huge_pmd(new_page, vma->vm_page_prot);
2071         entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
2072 
2073         /*
2074          * Clear the old entry under pagetable lock and establish the new PTE.
2075          * Any parallel GUP will either observe the old page blocking on the
2076          * page lock, block on the page table lock or observe the new page.
2077          * The SetPageUptodate on the new page and page_add_new_anon_rmap
2078          * guarantee the copy is visible before the pagetable update.
2079          */
2080         flush_cache_range(vma, mmun_start, mmun_end);
2081         page_add_anon_rmap(new_page, vma, mmun_start, true);
2082         pmdp_huge_clear_flush_notify(vma, mmun_start, pmd);
2083         set_pmd_at(mm, mmun_start, pmd, entry);
2084         update_mmu_cache_pmd(vma, address, &entry);
2085 
2086         page_ref_unfreeze(page, 2);
2087         mlock_migrate_page(new_page, page);
2088         page_remove_rmap(page, true);
2089         set_page_owner_migrate_reason(new_page, MR_NUMA_MISPLACED);
2090 
2091         spin_unlock(ptl);
2092         /*
2093          * No need to double call mmu_notifier->invalidate_range() callback as
2094          * the above pmdp_huge_clear_flush_notify() did already call it.
2095          */
2096         mmu_notifier_invalidate_range_only_end(mm, mmun_start, mmun_end);
2097 
2098         /* Take an "isolate" reference and put new page on the LRU. */
2099         get_page(new_page);
2100         putback_lru_page(new_page);
2101 
2102         unlock_page(new_page);
2103         unlock_page(page);
2104         put_page(page);                 /* Drop the rmap reference */
2105         put_page(page);                 /* Drop the LRU isolation reference */
2106 
2107         count_vm_events(PGMIGRATE_SUCCESS, HPAGE_PMD_NR);
2108         count_vm_numa_events(NUMA_PAGE_MIGRATE, HPAGE_PMD_NR);
2109 
2110         mod_node_page_state(page_pgdat(page),
2111                         NR_ISOLATED_ANON + page_lru,
2112                         -HPAGE_PMD_NR);
2113         return isolated;
2114 
2115 out_fail:
2116         count_vm_events(PGMIGRATE_FAIL, HPAGE_PMD_NR);
2117 out_dropref:
2118         ptl = pmd_lock(mm, pmd);
2119         if (pmd_same(*pmd, entry)) {
2120                 entry = pmd_modify(entry, vma->vm_page_prot);
2121                 set_pmd_at(mm, mmun_start, pmd, entry);
2122                 update_mmu_cache_pmd(vma, address, &entry);
2123         }
2124         spin_unlock(ptl);
2125 
2126 out_unlock:
2127         unlock_page(page);
2128         put_page(page);
2129         return 0;
2130 }
2131 #endif /* CONFIG_NUMA_BALANCING */
2132 
2133 #endif /* CONFIG_NUMA */
2134 
2135 #if defined(CONFIG_MIGRATE_VMA_HELPER)
2136 struct migrate_vma {
2137         struct vm_area_struct   *vma;
2138         unsigned long           *dst;
2139         unsigned long           *src;
2140         unsigned long           cpages;
2141         unsigned long           npages;
2142         unsigned long           start;
2143         unsigned long           end;
2144 };
2145 
2146 static int migrate_vma_collect_hole(unsigned long start,
2147                                     unsigned long end,
2148                                     struct mm_walk *walk)
2149 {
2150         struct migrate_vma *migrate = walk->private;
2151         unsigned long addr;
2152 
2153         for (addr = start & PAGE_MASK; addr < end; addr += PAGE_SIZE) {
2154                 migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE;
2155                 migrate->dst[migrate->npages] = 0;
2156                 migrate->npages++;
2157                 migrate->cpages++;
2158         }
2159 
2160         return 0;
2161 }
2162 
2163 static int migrate_vma_collect_skip(unsigned long start,
2164                                     unsigned long end,
2165                                     struct mm_walk *walk)
2166 {
2167         struct migrate_vma *migrate = walk->private;
2168         unsigned long addr;
2169 
2170         for (addr = start & PAGE_MASK; addr < end; addr += PAGE_SIZE) {
2171                 migrate->dst[migrate->npages] = 0;
2172                 migrate->src[migrate->npages++] = 0;
2173         }
2174 
2175         return 0;
2176 }
2177 
2178 static int migrate_vma_collect_pmd(pmd_t *pmdp,
2179                                    unsigned long start,
2180                                    unsigned long end,
2181                                    struct mm_walk *walk)
2182 {
2183         struct migrate_vma *migrate = walk->private;
2184         struct vm_area_struct *vma = walk->vma;
2185         struct mm_struct *mm = vma->vm_mm;
2186         unsigned long addr = start, unmapped = 0;
2187         spinlock_t *ptl;
2188         pte_t *ptep;
2189 
2190 again:
2191         if (pmd_none(*pmdp))
2192                 return migrate_vma_collect_hole(start, end, walk);
2193 
2194         if (pmd_trans_huge(*pmdp)) {
2195                 struct page *page;
2196 
2197                 ptl = pmd_lock(mm, pmdp);
2198                 if (unlikely(!pmd_trans_huge(*pmdp))) {
2199                         spin_unlock(ptl);
2200                         goto again;
2201                 }
2202 
2203                 page = pmd_page(*pmdp);
2204                 if (is_huge_zero_page(page)) {
2205                         spin_unlock(ptl);
2206                         split_huge_pmd(vma, pmdp, addr);
2207                         if (pmd_trans_unstable(pmdp))
2208                                 return migrate_vma_collect_skip(start, end,
2209                                                                 walk);
2210                 } else {
2211                         int ret;
2212 
2213                         get_page(page);
2214                         spin_unlock(ptl);
2215                         if (unlikely(!trylock_page(page)))
2216                                 return migrate_vma_collect_skip(start, end,
2217                                                                 walk);
2218                         ret = split_huge_page(page);
2219                         unlock_page(page);
2220                         put_page(page);
2221                         if (ret)
2222                                 return migrate_vma_collect_skip(start, end,
2223                                                                 walk);
2224                         if (pmd_none(*pmdp))
2225                                 return migrate_vma_collect_hole(start, end,
2226                                                                 walk);
2227                 }
2228         }
2229 
2230         if (unlikely(pmd_bad(*pmdp)))
2231                 return migrate_vma_collect_skip(start, end, walk);
2232 
2233         ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
2234         arch_enter_lazy_mmu_mode();
2235 
2236         for (; addr < end; addr += PAGE_SIZE, ptep++) {
2237                 unsigned long mpfn, pfn;
2238                 struct page *page;
2239                 swp_entry_t entry;
2240                 pte_t pte;
2241 
2242                 pte = *ptep;
2243                 pfn = pte_pfn(pte);
2244 
2245                 if (pte_none(pte)) {
2246                         mpfn = MIGRATE_PFN_MIGRATE;
2247                         migrate->cpages++;
2248                         pfn = 0;
2249                         goto next;
2250                 }
2251 
2252                 if (!pte_present(pte)) {
2253                         mpfn = pfn = 0;
2254 
2255                         /*
2256                          * Only care about unaddressable device page special
2257                          * page table entry. Other special swap entries are not
2258                          * migratable, and we ignore regular swapped page.
2259                          */
2260                         entry = pte_to_swp_entry(pte);
2261                         if (!is_device_private_entry(entry))
2262                                 goto next;
2263 
2264                         page = device_private_entry_to_page(entry);
2265                         mpfn = migrate_pfn(page_to_pfn(page))|
2266                                 MIGRATE_PFN_DEVICE | MIGRATE_PFN_MIGRATE;
2267                         if (is_write_device_private_entry(entry))
2268                                 mpfn |= MIGRATE_PFN_WRITE;
2269                 } else {
2270                         if (is_zero_pfn(pfn)) {
2271                                 mpfn = MIGRATE_PFN_MIGRATE;
2272                                 migrate->cpages++;
2273                                 pfn = 0;
2274                                 goto next;
2275                         }
2276                         page = _vm_normal_page(migrate->vma, addr, pte, true);
2277                         mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
2278                         mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
2279                 }
2280 
2281                 /* FIXME support THP */
2282                 if (!page || !page->mapping || PageTransCompound(page)) {
2283                         mpfn = pfn = 0;
2284                         goto next;
2285                 }
2286                 pfn = page_to_pfn(page);
2287 
2288                 /*
2289                  * By getting a reference on the page we pin it and that blocks
2290                  * any kind of migration. Side effect is that it "freezes" the
2291                  * pte.
2292                  *
2293                  * We drop this reference after isolating the page from the lru
2294                  * for non device page (device page are not on the lru and thus
2295                  * can't be dropped from it).
2296                  */
2297                 get_page(page);
2298                 migrate->cpages++;
2299 
2300                 /*
2301                  * Optimize for the common case where page is only mapped once
2302                  * in one process. If we can lock the page, then we can safely
2303                  * set up a special migration page table entry now.
2304                  */
2305                 if (trylock_page(page)) {
2306                         pte_t swp_pte;
2307 
2308                         mpfn |= MIGRATE_PFN_LOCKED;
2309                         ptep_get_and_clear(mm, addr, ptep);
2310 
2311                         /* Setup special migration page table entry */
2312                         entry = make_migration_entry(page, pte_write(pte));
2313                         swp_pte = swp_entry_to_pte(entry);
2314                         if (pte_soft_dirty(pte))
2315                                 swp_pte = pte_swp_mksoft_dirty(swp_pte);
2316                         set_pte_at(mm, addr, ptep, swp_pte);
2317 
2318                         /*
2319                          * This is like regular unmap: we remove the rmap and
2320                          * drop page refcount. Page won't be freed, as we took
2321                          * a reference just above.
2322                          */
2323                         page_remove_rmap(page, false);
2324                         put_page(page);
2325 
2326                         if (pte_present(pte))
2327                                 unmapped++;
2328                 }
2329 
2330 next:
2331                 migrate->dst[migrate->npages] = 0;
2332                 migrate->src[migrate->npages++] = mpfn;
2333         }
2334         arch_leave_lazy_mmu_mode();
2335         pte_unmap_unlock(ptep - 1, ptl);
2336 
2337         /* Only flush the TLB if we actually modified any entries */
2338         if (unmapped)
2339                 flush_tlb_range(walk->vma, start, end);
2340 
2341         return 0;
2342 }
2343 
2344 /*
2345  * migrate_vma_collect() - collect pages over a range of virtual addresses
2346  * @migrate: migrate struct containing all migration information
2347  *
2348  * This will walk the CPU page table. For each virtual address backed by a
2349  * valid page, it updates the src array and takes a reference on the page, in
2350  * order to pin the page until we lock it and unmap it.
2351  */
2352 static void migrate_vma_collect(struct migrate_vma *migrate)
2353 {
2354         struct mm_walk mm_walk;
2355 
2356         mm_walk.pmd_entry = migrate_vma_collect_pmd;
2357         mm_walk.pte_entry = NULL;
2358         mm_walk.pte_hole = migrate_vma_collect_hole;
2359         mm_walk.hugetlb_entry = NULL;
2360         mm_walk.test_walk = NULL;
2361         mm_walk.vma = migrate->vma;
2362         mm_walk.mm = migrate->vma->vm_mm;
2363         mm_walk.private = migrate;
2364 
2365         mmu_notifier_invalidate_range_start(mm_walk.mm,
2366                                             migrate->start,
2367                                             migrate->end);
2368         walk_page_range(migrate->start, migrate->end, &mm_walk);
2369         mmu_notifier_invalidate_range_end(mm_walk.mm,
2370                                           migrate->start,
2371                                           migrate->end);
2372 
2373         migrate->end = migrate->start + (migrate->npages << PAGE_SHIFT);
2374 }
2375 
2376 /*
2377  * migrate_vma_check_page() - check if page is pinned or not
2378  * @page: struct page to check
2379  *
2380  * Pinned pages cannot be migrated. This is the same test as in
2381  * migrate_page_move_mapping(), except that here we allow migration of a
2382  * ZONE_DEVICE page.
2383  */
2384 static bool migrate_vma_check_page(struct page *page)
2385 {
2386         /*
2387          * One extra ref because caller holds an extra reference, either from
2388          * isolate_lru_page() for a regular page, or migrate_vma_collect() for
2389          * a device page.
2390          */
2391         int extra = 1;
2392 
2393         /*
2394          * FIXME support THP (transparent huge page), it is bit more complex to
2395          * check them than regular pages, because they can be mapped with a pmd
2396          * or with a pte (split pte mapping).
2397          */
2398         if (PageCompound(page))
2399                 return false;
2400 
2401         /* Page from ZONE_DEVICE have one extra reference */
2402         if (is_zone_device_page(page)) {
2403                 /*
2404                  * Private page can never be pin as they have no valid pte and
2405                  * GUP will fail for those. Yet if there is a pending migration
2406                  * a thread might try to wait on the pte migration entry and
2407                  * will bump the page reference count. Sadly there is no way to
2408                  * differentiate a regular pin from migration wait. Hence to
2409                  * avoid 2 racing thread trying to migrate back to CPU to enter
2410                  * infinite loop (one stoping migration because the other is
2411                  * waiting on pte migration entry). We always return true here.
2412                  *
2413                  * FIXME proper solution is to rework migration_entry_wait() so
2414                  * it does not need to take a reference on page.
2415                  */
2416                 if (is_device_private_page(page))
2417                         return true;
2418 
2419                 /*
2420                  * Only allow device public page to be migrated and account for
2421                  * the extra reference count imply by ZONE_DEVICE pages.
2422                  */
2423                 if (!is_device_public_page(page))
2424                         return false;
2425                 extra++;
2426         }
2427 
2428         /* For file back page */
2429         if (page_mapping(page))
2430                 extra += 1 + page_has_private(page);
2431 
2432         if ((page_count(page) - extra) > page_mapcount(page))
2433                 return false;
2434 
2435         return true;
2436 }
2437 
2438 /*
2439  * migrate_vma_prepare() - lock pages and isolate them from the lru
2440  * @migrate: migrate struct containing all migration information
2441  *
2442  * This locks pages that have been collected by migrate_vma_collect(). Once each
2443  * page is locked it is isolated from the lru (for non-device pages). Finally,
2444  * the ref taken by migrate_vma_collect() is dropped, as locked pages cannot be
2445  * migrated by concurrent kernel threads.
2446  */
2447 static void migrate_vma_prepare(struct migrate_vma *migrate)
2448 {
2449         const unsigned long npages = migrate->npages;
2450         const unsigned long start = migrate->start;
2451         unsigned long addr, i, restore = 0;
2452         bool allow_drain = true;
2453 
2454         lru_add_drain();
2455 
2456         for (i = 0; (i < npages) && migrate->cpages; i++) {
2457                 struct page *page = migrate_pfn_to_page(migrate->src[i]);
2458                 bool remap = true;
2459 
2460                 if (!page)
2461                         continue;
2462 
2463                 if (!(migrate->src[i] & MIGRATE_PFN_LOCKED)) {
2464                         /*
2465                          * Because we are migrating several pages there can be
2466                          * a deadlock between 2 concurrent migration where each
2467                          * are waiting on each other page lock.
2468                          *
2469                          * Make migrate_vma() a best effort thing and backoff
2470                          * for any page we can not lock right away.
2471                          */
2472                         if (!trylock_page(page)) {
2473                                 migrate->src[i] = 0;
2474                                 migrate->cpages--;
2475                                 put_page(page);
2476                                 continue;
2477                         }
2478                         remap = false;
2479                         migrate->src[i] |= MIGRATE_PFN_LOCKED;
2480                 }
2481 
2482                 /* ZONE_DEVICE pages are not on LRU */
2483                 if (!is_zone_device_page(page)) {
2484                         if (!PageLRU(page) && allow_drain) {
2485                                 /* Drain CPU's pagevec */
2486                                 lru_add_drain_all();
2487                                 allow_drain = false;
2488                         }
2489 
2490                         if (isolate_lru_page(page)) {
2491                                 if (remap) {
2492                                         migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2493                                         migrate->cpages--;
2494                                         restore++;
2495                                 } else {
2496                                         migrate->src[i] = 0;
2497                                         unlock_page(page);
2498                                         migrate->cpages--;
2499                                         put_page(page);
2500                                 }
2501                                 continue;
2502                         }
2503 
2504                         /* Drop the reference we took in collect */
2505                         put_page(page);
2506                 }
2507 
2508                 if (!migrate_vma_check_page(page)) {
2509                         if (remap) {
2510                                 migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2511                                 migrate->cpages--;
2512                                 restore++;
2513 
2514                                 if (!is_zone_device_page(page)) {
2515                                         get_page(page);
2516                                         putback_lru_page(page);
2517                                 }
2518                         } else {
2519                                 migrate->src[i] = 0;
2520                                 unlock_page(page);
2521                                 migrate->cpages--;
2522 
2523                                 if (!is_zone_device_page(page))
2524                                         putback_lru_page(page);
2525                                 else
2526                                         put_page(page);
2527                         }
2528                 }
2529         }
2530 
2531         for (i = 0, addr = start; i < npages && restore; i++, addr += PAGE_SIZE) {
2532                 struct page *page = migrate_pfn_to_page(migrate->src[i]);
2533 
2534                 if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE))
2535                         continue;
2536 
2537                 remove_migration_pte(page, migrate->vma, addr, page);
2538 
2539                 migrate->src[i] = 0;
2540                 unlock_page(page);
2541                 put_page(page);
2542                 restore--;
2543         }
2544 }
2545 
2546 /*
2547  * migrate_vma_unmap() - replace page mapping with special migration pte entry
2548  * @migrate: migrate struct containing all migration information
2549  *
2550  * Replace page mapping (CPU page table pte) with a special migration pte entry
2551  * and check again if it has been pinned. Pinned pages are restored because we
2552  * cannot migrate them.
2553  *
2554  * This is the last step before we call the device driver callback to allocate
2555  * destination memory and copy contents of original page over to new page.
2556  */
2557 static void migrate_vma_unmap(struct migrate_vma *migrate)
2558 {
2559         int flags = TTU_MIGRATION | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
2560         const unsigned long npages = migrate->npages;
2561         const unsigned long start = migrate->start;
2562         unsigned long addr, i, restore = 0;
2563 
2564         for (i = 0; i < npages; i++) {
2565                 struct page *page = migrate_pfn_to_page(migrate->src[i]);
2566 
2567                 if (!page || !(migrate->src[i] & MIGRATE_PFN_MIGRATE))
2568                         continue;
2569 
2570                 if (page_mapped(page)) {
2571                         try_to_unmap(page, flags);
2572                         if (page_mapped(page))
2573                                 goto restore;
2574                 }
2575 
2576                 if (migrate_vma_check_page(page))
2577                         continue;
2578 
2579 restore:
2580                 migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2581                 migrate->cpages--;
2582                 restore++;
2583         }
2584 
2585         for (addr = start, i = 0; i < npages && restore; addr += PAGE_SIZE, i++) {
2586                 struct page *page = migrate_pfn_to_page(migrate->src[i]);
2587 
2588                 if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE))
2589                         continue;
2590 
2591                 remove_migration_ptes(page, page, false);
2592 
2593                 migrate->src[i] = 0;
2594                 unlock_page(page);
2595                 restore--;
2596 
2597                 if (is_zone_device_page(page))
2598                         put_page(page);
2599                 else
2600                         putback_lru_page(page);
2601         }
2602 }
2603 
2604 static void migrate_vma_insert_page(struct migrate_vma *migrate,
2605                                     unsigned long addr,
2606                                     struct page *page,
2607                                     unsigned long *src,
2608                                     unsigned long *dst)
2609 {
2610         struct vm_area_struct *vma = migrate->vma;
2611         struct mm_struct *mm = vma->vm_mm;
2612         struct mem_cgroup *memcg;
2613         bool flush = false;
2614         spinlock_t *ptl;
2615         pte_t entry;
2616         pgd_t *pgdp;
2617         p4d_t *p4dp;
2618         pud_t *pudp;
2619         pmd_t *pmdp;
2620         pte_t *ptep;
2621 
2622         /* Only allow populating anonymous memory */
2623         if (!vma_is_anonymous(vma))
2624                 goto abort;
2625 
2626         pgdp = pgd_offset(mm, addr);
2627         p4dp = p4d_alloc(mm, pgdp, addr);
2628         if (!p4dp)
2629                 goto abort;
2630         pudp = pud_alloc(mm, p4dp, addr);
2631         if (!pudp)
2632                 goto abort;
2633         pmdp = pmd_alloc(mm, pudp, addr);
2634         if (!pmdp)
2635                 goto abort;
2636 
2637         if (pmd_trans_huge(*pmdp) || pmd_devmap(*pmdp))
2638                 goto abort;
2639 
2640         /*
2641          * Use pte_alloc() instead of pte_alloc_map().  We can't run
2642          * pte_offset_map() on pmds where a huge pmd might be created
2643          * from a different thread.
2644          *
2645          * pte_alloc_map() is safe to use under down_write(mmap_sem) or when
2646          * parallel threads are excluded by other means.
2647          *
2648          * Here we only have down_read(mmap_sem).
2649          */
2650         if (pte_alloc(mm, pmdp, addr))
2651                 goto abort;
2652 
2653         /* See the comment in pte_alloc_one_map() */
2654         if (unlikely(pmd_trans_unstable(pmdp)))
2655                 goto abort;
2656 
2657         if (unlikely(anon_vma_prepare(vma)))
2658                 goto abort;
2659         if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL, &memcg, false))
2660                 goto abort;
2661 
2662         /*
2663          * The memory barrier inside __SetPageUptodate makes sure that
2664          * preceding stores to the page contents become visible before
2665          * the set_pte_at() write.
2666          */
2667         __SetPageUptodate(page);
2668 
2669         if (is_zone_device_page(page)) {
2670                 if (is_device_private_page(page)) {
2671                         swp_entry_t swp_entry;
2672 
2673                         swp_entry = make_device_private_entry(page, vma->vm_flags & VM_WRITE);
2674                         entry = swp_entry_to_pte(swp_entry);
2675                 } else if (is_device_public_page(page)) {
2676                         entry = pte_mkold(mk_pte(page, READ_ONCE(vma->vm_page_prot)));
2677                         if (vma->vm_flags & VM_WRITE)
2678                                 entry = pte_mkwrite(pte_mkdirty(entry));
2679                         entry = pte_mkdevmap(entry);
2680                 }
2681         } else {
2682                 entry = mk_pte(page, vma->vm_page_prot);
2683                 if (vma->vm_flags & VM_WRITE)
2684                         entry = pte_mkwrite(pte_mkdirty(entry));
2685         }
2686 
2687         ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
2688 
2689         if (pte_present(*ptep)) {
2690                 unsigned long pfn = pte_pfn(*ptep);
2691 
2692                 if (!is_zero_pfn(pfn)) {
2693                         pte_unmap_unlock(ptep, ptl);
2694                         mem_cgroup_cancel_charge(page, memcg, false);
2695                         goto abort;
2696                 }
2697                 flush = true;
2698         } else if (!pte_none(*ptep)) {
2699                 pte_unmap_unlock(ptep, ptl);
2700                 mem_cgroup_cancel_charge(page, memcg, false);
2701                 goto abort;
2702         }
2703 
2704         /*
2705          * Check for usefaultfd but do not deliver the fault. Instead,
2706          * just back off.
2707          */
2708         if (userfaultfd_missing(vma)) {
2709                 pte_unmap_unlock(ptep, ptl);
2710                 mem_cgroup_cancel_charge(page, memcg, false);
2711                 goto abort;
2712         }
2713 
2714         inc_mm_counter(mm, MM_ANONPAGES);
2715         page_add_new_anon_rmap(page, vma, addr, false);
2716         mem_cgroup_commit_charge(page, memcg, false, false);
2717         if (!is_zone_device_page(page))
2718                 lru_cache_add_active_or_unevictable(page, vma);
2719         get_page(page);
2720 
2721         if (flush) {
2722                 flush_cache_page(vma, addr, pte_pfn(*ptep));
2723                 ptep_clear_flush_notify(vma, addr, ptep);
2724                 set_pte_at_notify(mm, addr, ptep, entry);
2725                 update_mmu_cache(vma, addr, ptep);
2726         } else {
2727                 /* No need to invalidate - it was non-present before */
2728                 set_pte_at(mm, addr, ptep, entry);
2729                 update_mmu_cache(vma, addr, ptep);
2730         }
2731 
2732         pte_unmap_unlock(ptep, ptl);
2733         *src = MIGRATE_PFN_MIGRATE;
2734         return;
2735 
2736 abort:
2737         *src &= ~MIGRATE_PFN_MIGRATE;
2738 }
2739 
2740 /*
2741  * migrate_vma_pages() - migrate meta-data from src page to dst page
2742  * @migrate: migrate struct containing all migration information
2743  *
2744  * This migrates struct page meta-data from source struct page to destination
2745  * struct page. This effectively finishes the migration from source page to the
2746  * destination page.
2747  */
2748 static void migrate_vma_pages(struct migrate_vma *migrate)
2749 {
2750         const unsigned long npages = migrate->npages;
2751         const unsigned long start = migrate->start;
2752         struct vm_area_struct *vma = migrate->vma;
2753         struct mm_struct *mm = vma->vm_mm;
2754         unsigned long addr, i, mmu_start;
2755         bool notified = false;
2756 
2757         for (i = 0, addr = start; i < npages; addr += PAGE_SIZE, i++) {
2758                 struct page *newpage = migrate_pfn_to_page(migrate->dst[i]);
2759                 struct page *page = migrate_pfn_to_page(migrate->src[i]);
2760                 struct address_space *mapping;
2761                 int r;
2762 
2763                 if (!newpage) {
2764                         migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2765                         continue;
2766                 }
2767 
2768                 if (!page) {
2769                         if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE)) {
2770                                 continue;
2771                         }
2772                         if (!notified) {
2773                                 mmu_start = addr;
2774                                 notified = true;
2775                                 mmu_notifier_invalidate_range_start(mm,
2776                                                                 mmu_start,
2777                                                                 migrate->end);
2778                         }
2779                         migrate_vma_insert_page(migrate, addr, newpage,
2780                                                 &migrate->src[i],
2781                                                 &migrate->dst[i]);
2782                         continue;
2783                 }
2784 
2785                 mapping = page_mapping(page);
2786 
2787                 if (is_zone_device_page(newpage)) {
2788                         if (is_device_private_page(newpage)) {
2789                                 /*
2790                                  * For now only support private anonymous when
2791                                  * migrating to un-addressable device memory.
2792                                  */
2793                                 if (mapping) {
2794                                         migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2795                                         continue;
2796                                 }
2797                         } else if (!is_device_public_page(newpage)) {
2798                                 /*
2799                                  * Other types of ZONE_DEVICE page are not
2800                                  * supported.
2801                                  */
2802                                 migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2803                                 continue;
2804                         }
2805                 }
2806 
2807                 r = migrate_page(mapping, newpage, page, MIGRATE_SYNC_NO_COPY);
2808                 if (r != MIGRATEPAGE_SUCCESS)
2809                         migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2810         }
2811 
2812         /*
2813          * No need to double call mmu_notifier->invalidate_range() callback as
2814          * the above ptep_clear_flush_notify() inside migrate_vma_insert_page()
2815          * did already call it.
2816          */
2817         if (notified)
2818                 mmu_notifier_invalidate_range_only_end(mm, mmu_start,
2819                                                        migrate->end);
2820 }
2821 
2822 /*
2823  * migrate_vma_finalize() - restore CPU page table entry
2824  * @migrate: migrate struct containing all migration information
2825  *
2826  * This replaces the special migration pte entry with either a mapping to the
2827  * new page if migration was successful for that page, or to the original page
2828  * otherwise.
2829  *
2830  * This also unlocks the pages and puts them back on the lru, or drops the extra
2831  * refcount, for device pages.
2832  */
2833 static void migrate_vma_finalize(struct migrate_vma *migrate)
2834 {
2835         const unsigned long npages = migrate->npages;
2836         unsigned long i;
2837 
2838         for (i = 0; i < npages; i++) {
2839                 struct page *newpage = migrate_pfn_to_page(migrate->dst[i]);
2840                 struct page *page = migrate_pfn_to_page(migrate->src[i]);
2841 
2842                 if (!page) {
2843                         if (newpage) {
2844                                 unlock_page(newpage);
2845                                 put_page(newpage);
2846                         }
2847                         continue;
2848                 }
2849 
2850                 if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE) || !newpage) {
2851                         if (newpage) {
2852                                 unlock_page(newpage);
2853                                 put_page(newpage);
2854                         }
2855                         newpage = page;
2856                 }
2857 
2858                 remove_migration_ptes(page, newpage, false);
2859                 unlock_page(page);
2860                 migrate->cpages--;
2861 
2862                 if (is_zone_device_page(page))
2863                         put_page(page);
2864                 else
2865                         putback_lru_page(page);
2866 
2867                 if (newpage != page) {
2868                         unlock_page(newpage);
2869                         if (is_zone_device_page(newpage))
2870                                 put_page(newpage);
2871                         else
2872                                 putback_lru_page(newpage);
2873                 }
2874         }
2875 }
2876 
2877 /*
2878  * migrate_vma() - migrate a range of memory inside vma
2879  *
2880  * @ops: migration callback for allocating destination memory and copying
2881  * @vma: virtual memory area containing the range to be migrated
2882  * @start: start address of the range to migrate (inclusive)
2883  * @end: end address of the range to migrate (exclusive)
2884  * @src: array of hmm_pfn_t containing source pfns
2885  * @dst: array of hmm_pfn_t containing destination pfns
2886  * @private: pointer passed back to each of the callback
2887  * Returns: 0 on success, error code otherwise
2888  *
2889  * This function tries to migrate a range of memory virtual address range, using
2890  * callbacks to allocate and copy memory from source to destination. First it
2891  * collects all the pages backing each virtual address in the range, saving this
2892  * inside the src array. Then it locks those pages and unmaps them. Once the pages
2893  * are locked and unmapped, it checks whether each page is pinned or not. Pages
2894  * that aren't pinned have the MIGRATE_PFN_MIGRATE flag set (by this function)
2895  * in the corresponding src array entry. It then restores any pages that are
2896  * pinned, by remapping and unlocking those pages.
2897  *
2898  * At this point it calls the alloc_and_copy() callback. For documentation on
2899  * what is expected from that callback, see struct migrate_vma_ops comments in
2900  * include/linux/migrate.h
2901  *
2902  * After the alloc_and_copy() callback, this function goes over each entry in
2903  * the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag
2904  * set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag set,
2905  * then the function tries to migrate struct page information from the source
2906  * struct page to the destination struct page. If it fails to migrate the struct
2907  * page information, then it clears the MIGRATE_PFN_MIGRATE flag in the src
2908  * array.
2909  *
2910  * At this point all successfully migrated pages have an entry in the src
2911  * array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the dst
2912  * array entry with MIGRATE_PFN_VALID flag set.
2913  *
2914  * It then calls the finalize_and_map() callback. See comments for "struct
2915  * migrate_vma_ops", in include/linux/migrate.h for details about
2916  * finalize_and_map() behavior.
2917  *
2918  * After the finalize_and_map() callback, for successfully migrated pages, this
2919  * function updates the CPU page table to point to new pages, otherwise it
2920  * restores the CPU page table to point to the original source pages.
2921  *
2922  * Function returns 0 after the above steps, even if no pages were migrated
2923  * (The function only returns an error if any of the arguments are invalid.)
2924  *
2925  * Both src and dst array must be big enough for (end - start) >> PAGE_SHIFT
2926  * unsigned long entries.
2927  */
2928 int migrate_vma(const struct migrate_vma_ops *ops,
2929                 struct vm_area_struct *vma,
2930                 unsigned long start,
2931                 unsigned long end,
2932                 unsigned long *src,
2933                 unsigned long *dst,
2934                 void *private)
2935 {
2936         struct migrate_vma migrate;
2937 
2938         /* Sanity check the arguments */
2939         start &= PAGE_MASK;
2940         end &= PAGE_MASK;
2941         if (!vma || is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL))
2942                 return -EINVAL;
2943         if (start < vma->vm_start || start >= vma->vm_end)
2944                 return -EINVAL;
2945         if (end <= vma->vm_start || end > vma->vm_end)
2946                 return -EINVAL;
2947         if (!ops || !src || !dst || start >= end)
2948                 return -EINVAL;
2949 
2950         memset(src, 0, sizeof(*src) * ((end - start) >> PAGE_SHIFT));
2951         migrate.src = src;
2952         migrate.dst = dst;
2953         migrate.start = start;
2954         migrate.npages = 0;
2955         migrate.cpages = 0;
2956         migrate.end = end;
2957         migrate.vma = vma;
2958 
2959         /* Collect, and try to unmap source pages */
2960         migrate_vma_collect(&migrate);
2961         if (!migrate.cpages)
2962                 return 0;
2963 
2964         /* Lock and isolate page */
2965         migrate_vma_prepare(&migrate);
2966         if (!migrate.cpages)
2967                 return 0;
2968 
2969         /* Unmap pages */
2970         migrate_vma_unmap(&migrate);
2971         if (!migrate.cpages)
2972                 return 0;
2973 
2974         /*
2975          * At this point pages are locked and unmapped, and thus they have
2976          * stable content and can safely be copied to destination memory that
2977          * is allocated by the callback.
2978          *
2979          * Note that migration can fail in migrate_vma_struct_page() for each
2980          * individual page.
2981          */
2982         ops->alloc_and_copy(vma, src, dst, start, end, private);
2983 
2984         /* This does the real migration of struct page */
2985         migrate_vma_pages(&migrate);
2986 
2987         ops->finalize_and_map(vma, src, dst, start, end, private);
2988 
2989         /* Unlock and remap pages */
2990         migrate_vma_finalize(&migrate);
2991 
2992         return 0;
2993 }
2994 EXPORT_SYMBOL(migrate_vma);
2995 #endif /* defined(MIGRATE_VMA_HELPER) */
2996 

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