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TOMOYO Linux Cross Reference
Linux/mm/khugepaged.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  3 
  4 #include <linux/mm.h>
  5 #include <linux/sched.h>
  6 #include <linux/sched/mm.h>
  7 #include <linux/sched/coredump.h>
  8 #include <linux/mmu_notifier.h>
  9 #include <linux/rmap.h>
 10 #include <linux/swap.h>
 11 #include <linux/mm_inline.h>
 12 #include <linux/kthread.h>
 13 #include <linux/khugepaged.h>
 14 #include <linux/freezer.h>
 15 #include <linux/mman.h>
 16 #include <linux/hashtable.h>
 17 #include <linux/userfaultfd_k.h>
 18 #include <linux/page_idle.h>
 19 #include <linux/swapops.h>
 20 #include <linux/shmem_fs.h>
 21 
 22 #include <asm/tlb.h>
 23 #include <asm/pgalloc.h>
 24 #include "internal.h"
 25 
 26 enum scan_result {
 27         SCAN_FAIL,
 28         SCAN_SUCCEED,
 29         SCAN_PMD_NULL,
 30         SCAN_EXCEED_NONE_PTE,
 31         SCAN_PTE_NON_PRESENT,
 32         SCAN_PAGE_RO,
 33         SCAN_LACK_REFERENCED_PAGE,
 34         SCAN_PAGE_NULL,
 35         SCAN_SCAN_ABORT,
 36         SCAN_PAGE_COUNT,
 37         SCAN_PAGE_LRU,
 38         SCAN_PAGE_LOCK,
 39         SCAN_PAGE_ANON,
 40         SCAN_PAGE_COMPOUND,
 41         SCAN_ANY_PROCESS,
 42         SCAN_VMA_NULL,
 43         SCAN_VMA_CHECK,
 44         SCAN_ADDRESS_RANGE,
 45         SCAN_SWAP_CACHE_PAGE,
 46         SCAN_DEL_PAGE_LRU,
 47         SCAN_ALLOC_HUGE_PAGE_FAIL,
 48         SCAN_CGROUP_CHARGE_FAIL,
 49         SCAN_EXCEED_SWAP_PTE,
 50         SCAN_TRUNCATED,
 51 };
 52 
 53 #define CREATE_TRACE_POINTS
 54 #include <trace/events/huge_memory.h>
 55 
 56 /* default scan 8*512 pte (or vmas) every 30 second */
 57 static unsigned int khugepaged_pages_to_scan __read_mostly;
 58 static unsigned int khugepaged_pages_collapsed;
 59 static unsigned int khugepaged_full_scans;
 60 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
 61 /* during fragmentation poll the hugepage allocator once every minute */
 62 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
 63 static unsigned long khugepaged_sleep_expire;
 64 static DEFINE_SPINLOCK(khugepaged_mm_lock);
 65 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
 66 /*
 67  * default collapse hugepages if there is at least one pte mapped like
 68  * it would have happened if the vma was large enough during page
 69  * fault.
 70  */
 71 static unsigned int khugepaged_max_ptes_none __read_mostly;
 72 static unsigned int khugepaged_max_ptes_swap __read_mostly;
 73 
 74 #define MM_SLOTS_HASH_BITS 10
 75 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
 76 
 77 static struct kmem_cache *mm_slot_cache __read_mostly;
 78 
 79 /**
 80  * struct mm_slot - hash lookup from mm to mm_slot
 81  * @hash: hash collision list
 82  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
 83  * @mm: the mm that this information is valid for
 84  */
 85 struct mm_slot {
 86         struct hlist_node hash;
 87         struct list_head mm_node;
 88         struct mm_struct *mm;
 89 };
 90 
 91 /**
 92  * struct khugepaged_scan - cursor for scanning
 93  * @mm_head: the head of the mm list to scan
 94  * @mm_slot: the current mm_slot we are scanning
 95  * @address: the next address inside that to be scanned
 96  *
 97  * There is only the one khugepaged_scan instance of this cursor structure.
 98  */
 99 struct khugepaged_scan {
100         struct list_head mm_head;
101         struct mm_slot *mm_slot;
102         unsigned long address;
103 };
104 
105 static struct khugepaged_scan khugepaged_scan = {
106         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
107 };
108 
109 #ifdef CONFIG_SYSFS
110 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
111                                          struct kobj_attribute *attr,
112                                          char *buf)
113 {
114         return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
115 }
116 
117 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
118                                           struct kobj_attribute *attr,
119                                           const char *buf, size_t count)
120 {
121         unsigned long msecs;
122         int err;
123 
124         err = kstrtoul(buf, 10, &msecs);
125         if (err || msecs > UINT_MAX)
126                 return -EINVAL;
127 
128         khugepaged_scan_sleep_millisecs = msecs;
129         khugepaged_sleep_expire = 0;
130         wake_up_interruptible(&khugepaged_wait);
131 
132         return count;
133 }
134 static struct kobj_attribute scan_sleep_millisecs_attr =
135         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
136                scan_sleep_millisecs_store);
137 
138 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
139                                           struct kobj_attribute *attr,
140                                           char *buf)
141 {
142         return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
143 }
144 
145 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
146                                            struct kobj_attribute *attr,
147                                            const char *buf, size_t count)
148 {
149         unsigned long msecs;
150         int err;
151 
152         err = kstrtoul(buf, 10, &msecs);
153         if (err || msecs > UINT_MAX)
154                 return -EINVAL;
155 
156         khugepaged_alloc_sleep_millisecs = msecs;
157         khugepaged_sleep_expire = 0;
158         wake_up_interruptible(&khugepaged_wait);
159 
160         return count;
161 }
162 static struct kobj_attribute alloc_sleep_millisecs_attr =
163         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
164                alloc_sleep_millisecs_store);
165 
166 static ssize_t pages_to_scan_show(struct kobject *kobj,
167                                   struct kobj_attribute *attr,
168                                   char *buf)
169 {
170         return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
171 }
172 static ssize_t pages_to_scan_store(struct kobject *kobj,
173                                    struct kobj_attribute *attr,
174                                    const char *buf, size_t count)
175 {
176         int err;
177         unsigned long pages;
178 
179         err = kstrtoul(buf, 10, &pages);
180         if (err || !pages || pages > UINT_MAX)
181                 return -EINVAL;
182 
183         khugepaged_pages_to_scan = pages;
184 
185         return count;
186 }
187 static struct kobj_attribute pages_to_scan_attr =
188         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
189                pages_to_scan_store);
190 
191 static ssize_t pages_collapsed_show(struct kobject *kobj,
192                                     struct kobj_attribute *attr,
193                                     char *buf)
194 {
195         return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
196 }
197 static struct kobj_attribute pages_collapsed_attr =
198         __ATTR_RO(pages_collapsed);
199 
200 static ssize_t full_scans_show(struct kobject *kobj,
201                                struct kobj_attribute *attr,
202                                char *buf)
203 {
204         return sprintf(buf, "%u\n", khugepaged_full_scans);
205 }
206 static struct kobj_attribute full_scans_attr =
207         __ATTR_RO(full_scans);
208 
209 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
210                                       struct kobj_attribute *attr, char *buf)
211 {
212         return single_hugepage_flag_show(kobj, attr, buf,
213                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
214 }
215 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
216                                        struct kobj_attribute *attr,
217                                        const char *buf, size_t count)
218 {
219         return single_hugepage_flag_store(kobj, attr, buf, count,
220                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
221 }
222 static struct kobj_attribute khugepaged_defrag_attr =
223         __ATTR(defrag, 0644, khugepaged_defrag_show,
224                khugepaged_defrag_store);
225 
226 /*
227  * max_ptes_none controls if khugepaged should collapse hugepages over
228  * any unmapped ptes in turn potentially increasing the memory
229  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
230  * reduce the available free memory in the system as it
231  * runs. Increasing max_ptes_none will instead potentially reduce the
232  * free memory in the system during the khugepaged scan.
233  */
234 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
235                                              struct kobj_attribute *attr,
236                                              char *buf)
237 {
238         return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
239 }
240 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
241                                               struct kobj_attribute *attr,
242                                               const char *buf, size_t count)
243 {
244         int err;
245         unsigned long max_ptes_none;
246 
247         err = kstrtoul(buf, 10, &max_ptes_none);
248         if (err || max_ptes_none > HPAGE_PMD_NR-1)
249                 return -EINVAL;
250 
251         khugepaged_max_ptes_none = max_ptes_none;
252 
253         return count;
254 }
255 static struct kobj_attribute khugepaged_max_ptes_none_attr =
256         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
257                khugepaged_max_ptes_none_store);
258 
259 static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
260                                              struct kobj_attribute *attr,
261                                              char *buf)
262 {
263         return sprintf(buf, "%u\n", khugepaged_max_ptes_swap);
264 }
265 
266 static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
267                                               struct kobj_attribute *attr,
268                                               const char *buf, size_t count)
269 {
270         int err;
271         unsigned long max_ptes_swap;
272 
273         err  = kstrtoul(buf, 10, &max_ptes_swap);
274         if (err || max_ptes_swap > HPAGE_PMD_NR-1)
275                 return -EINVAL;
276 
277         khugepaged_max_ptes_swap = max_ptes_swap;
278 
279         return count;
280 }
281 
282 static struct kobj_attribute khugepaged_max_ptes_swap_attr =
283         __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
284                khugepaged_max_ptes_swap_store);
285 
286 static struct attribute *khugepaged_attr[] = {
287         &khugepaged_defrag_attr.attr,
288         &khugepaged_max_ptes_none_attr.attr,
289         &pages_to_scan_attr.attr,
290         &pages_collapsed_attr.attr,
291         &full_scans_attr.attr,
292         &scan_sleep_millisecs_attr.attr,
293         &alloc_sleep_millisecs_attr.attr,
294         &khugepaged_max_ptes_swap_attr.attr,
295         NULL,
296 };
297 
298 struct attribute_group khugepaged_attr_group = {
299         .attrs = khugepaged_attr,
300         .name = "khugepaged",
301 };
302 #endif /* CONFIG_SYSFS */
303 
304 #define VM_NO_KHUGEPAGED (VM_SPECIAL | VM_HUGETLB)
305 
306 int hugepage_madvise(struct vm_area_struct *vma,
307                      unsigned long *vm_flags, int advice)
308 {
309         switch (advice) {
310         case MADV_HUGEPAGE:
311 #ifdef CONFIG_S390
312                 /*
313                  * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
314                  * can't handle this properly after s390_enable_sie, so we simply
315                  * ignore the madvise to prevent qemu from causing a SIGSEGV.
316                  */
317                 if (mm_has_pgste(vma->vm_mm))
318                         return 0;
319 #endif
320                 *vm_flags &= ~VM_NOHUGEPAGE;
321                 *vm_flags |= VM_HUGEPAGE;
322                 /*
323                  * If the vma become good for khugepaged to scan,
324                  * register it here without waiting a page fault that
325                  * may not happen any time soon.
326                  */
327                 if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
328                                 khugepaged_enter_vma_merge(vma, *vm_flags))
329                         return -ENOMEM;
330                 break;
331         case MADV_NOHUGEPAGE:
332                 *vm_flags &= ~VM_HUGEPAGE;
333                 *vm_flags |= VM_NOHUGEPAGE;
334                 /*
335                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
336                  * this vma even if we leave the mm registered in khugepaged if
337                  * it got registered before VM_NOHUGEPAGE was set.
338                  */
339                 break;
340         }
341 
342         return 0;
343 }
344 
345 int __init khugepaged_init(void)
346 {
347         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
348                                           sizeof(struct mm_slot),
349                                           __alignof__(struct mm_slot), 0, NULL);
350         if (!mm_slot_cache)
351                 return -ENOMEM;
352 
353         khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
354         khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
355         khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
356 
357         return 0;
358 }
359 
360 void __init khugepaged_destroy(void)
361 {
362         kmem_cache_destroy(mm_slot_cache);
363 }
364 
365 static inline struct mm_slot *alloc_mm_slot(void)
366 {
367         if (!mm_slot_cache)     /* initialization failed */
368                 return NULL;
369         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
370 }
371 
372 static inline void free_mm_slot(struct mm_slot *mm_slot)
373 {
374         kmem_cache_free(mm_slot_cache, mm_slot);
375 }
376 
377 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
378 {
379         struct mm_slot *mm_slot;
380 
381         hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
382                 if (mm == mm_slot->mm)
383                         return mm_slot;
384 
385         return NULL;
386 }
387 
388 static void insert_to_mm_slots_hash(struct mm_struct *mm,
389                                     struct mm_slot *mm_slot)
390 {
391         mm_slot->mm = mm;
392         hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
393 }
394 
395 static inline int khugepaged_test_exit(struct mm_struct *mm)
396 {
397         return atomic_read(&mm->mm_users) == 0;
398 }
399 
400 int __khugepaged_enter(struct mm_struct *mm)
401 {
402         struct mm_slot *mm_slot;
403         int wakeup;
404 
405         mm_slot = alloc_mm_slot();
406         if (!mm_slot)
407                 return -ENOMEM;
408 
409         /* __khugepaged_exit() must not run from under us */
410         VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
411         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
412                 free_mm_slot(mm_slot);
413                 return 0;
414         }
415 
416         spin_lock(&khugepaged_mm_lock);
417         insert_to_mm_slots_hash(mm, mm_slot);
418         /*
419          * Insert just behind the scanning cursor, to let the area settle
420          * down a little.
421          */
422         wakeup = list_empty(&khugepaged_scan.mm_head);
423         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
424         spin_unlock(&khugepaged_mm_lock);
425 
426         mmgrab(mm);
427         if (wakeup)
428                 wake_up_interruptible(&khugepaged_wait);
429 
430         return 0;
431 }
432 
433 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
434                                unsigned long vm_flags)
435 {
436         unsigned long hstart, hend;
437         if (!vma->anon_vma)
438                 /*
439                  * Not yet faulted in so we will register later in the
440                  * page fault if needed.
441                  */
442                 return 0;
443         if (vma->vm_ops || (vm_flags & VM_NO_KHUGEPAGED))
444                 /* khugepaged not yet working on file or special mappings */
445                 return 0;
446         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
447         hend = vma->vm_end & HPAGE_PMD_MASK;
448         if (hstart < hend)
449                 return khugepaged_enter(vma, vm_flags);
450         return 0;
451 }
452 
453 void __khugepaged_exit(struct mm_struct *mm)
454 {
455         struct mm_slot *mm_slot;
456         int free = 0;
457 
458         spin_lock(&khugepaged_mm_lock);
459         mm_slot = get_mm_slot(mm);
460         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
461                 hash_del(&mm_slot->hash);
462                 list_del(&mm_slot->mm_node);
463                 free = 1;
464         }
465         spin_unlock(&khugepaged_mm_lock);
466 
467         if (free) {
468                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
469                 free_mm_slot(mm_slot);
470                 mmdrop(mm);
471         } else if (mm_slot) {
472                 /*
473                  * This is required to serialize against
474                  * khugepaged_test_exit() (which is guaranteed to run
475                  * under mmap sem read mode). Stop here (after we
476                  * return all pagetables will be destroyed) until
477                  * khugepaged has finished working on the pagetables
478                  * under the mmap_sem.
479                  */
480                 down_write(&mm->mmap_sem);
481                 up_write(&mm->mmap_sem);
482         }
483 }
484 
485 static void release_pte_page(struct page *page)
486 {
487         dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_cache(page));
488         unlock_page(page);
489         putback_lru_page(page);
490 }
491 
492 static void release_pte_pages(pte_t *pte, pte_t *_pte)
493 {
494         while (--_pte >= pte) {
495                 pte_t pteval = *_pte;
496                 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
497                         release_pte_page(pte_page(pteval));
498         }
499 }
500 
501 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
502                                         unsigned long address,
503                                         pte_t *pte)
504 {
505         struct page *page = NULL;
506         pte_t *_pte;
507         int none_or_zero = 0, result = 0, referenced = 0;
508         bool writable = false;
509 
510         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
511              _pte++, address += PAGE_SIZE) {
512                 pte_t pteval = *_pte;
513                 if (pte_none(pteval) || (pte_present(pteval) &&
514                                 is_zero_pfn(pte_pfn(pteval)))) {
515                         if (!userfaultfd_armed(vma) &&
516                             ++none_or_zero <= khugepaged_max_ptes_none) {
517                                 continue;
518                         } else {
519                                 result = SCAN_EXCEED_NONE_PTE;
520                                 goto out;
521                         }
522                 }
523                 if (!pte_present(pteval)) {
524                         result = SCAN_PTE_NON_PRESENT;
525                         goto out;
526                 }
527                 page = vm_normal_page(vma, address, pteval);
528                 if (unlikely(!page)) {
529                         result = SCAN_PAGE_NULL;
530                         goto out;
531                 }
532 
533                 /* TODO: teach khugepaged to collapse THP mapped with pte */
534                 if (PageCompound(page)) {
535                         result = SCAN_PAGE_COMPOUND;
536                         goto out;
537                 }
538 
539                 VM_BUG_ON_PAGE(!PageAnon(page), page);
540 
541                 /*
542                  * We can do it before isolate_lru_page because the
543                  * page can't be freed from under us. NOTE: PG_lock
544                  * is needed to serialize against split_huge_page
545                  * when invoked from the VM.
546                  */
547                 if (!trylock_page(page)) {
548                         result = SCAN_PAGE_LOCK;
549                         goto out;
550                 }
551 
552                 /*
553                  * cannot use mapcount: can't collapse if there's a gup pin.
554                  * The page must only be referenced by the scanned process
555                  * and page swap cache.
556                  */
557                 if (page_count(page) != 1 + PageSwapCache(page)) {
558                         unlock_page(page);
559                         result = SCAN_PAGE_COUNT;
560                         goto out;
561                 }
562                 if (pte_write(pteval)) {
563                         writable = true;
564                 } else {
565                         if (PageSwapCache(page) &&
566                             !reuse_swap_page(page, NULL)) {
567                                 unlock_page(page);
568                                 result = SCAN_SWAP_CACHE_PAGE;
569                                 goto out;
570                         }
571                         /*
572                          * Page is not in the swap cache. It can be collapsed
573                          * into a THP.
574                          */
575                 }
576 
577                 /*
578                  * Isolate the page to avoid collapsing an hugepage
579                  * currently in use by the VM.
580                  */
581                 if (isolate_lru_page(page)) {
582                         unlock_page(page);
583                         result = SCAN_DEL_PAGE_LRU;
584                         goto out;
585                 }
586                 inc_node_page_state(page,
587                                 NR_ISOLATED_ANON + page_is_file_cache(page));
588                 VM_BUG_ON_PAGE(!PageLocked(page), page);
589                 VM_BUG_ON_PAGE(PageLRU(page), page);
590 
591                 /* There should be enough young pte to collapse the page */
592                 if (pte_young(pteval) ||
593                     page_is_young(page) || PageReferenced(page) ||
594                     mmu_notifier_test_young(vma->vm_mm, address))
595                         referenced++;
596         }
597         if (likely(writable)) {
598                 if (likely(referenced)) {
599                         result = SCAN_SUCCEED;
600                         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
601                                                             referenced, writable, result);
602                         return 1;
603                 }
604         } else {
605                 result = SCAN_PAGE_RO;
606         }
607 
608 out:
609         release_pte_pages(pte, _pte);
610         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
611                                             referenced, writable, result);
612         return 0;
613 }
614 
615 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
616                                       struct vm_area_struct *vma,
617                                       unsigned long address,
618                                       spinlock_t *ptl)
619 {
620         pte_t *_pte;
621         for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
622                                 _pte++, page++, address += PAGE_SIZE) {
623                 pte_t pteval = *_pte;
624                 struct page *src_page;
625 
626                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
627                         clear_user_highpage(page, address);
628                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
629                         if (is_zero_pfn(pte_pfn(pteval))) {
630                                 /*
631                                  * ptl mostly unnecessary.
632                                  */
633                                 spin_lock(ptl);
634                                 /*
635                                  * paravirt calls inside pte_clear here are
636                                  * superfluous.
637                                  */
638                                 pte_clear(vma->vm_mm, address, _pte);
639                                 spin_unlock(ptl);
640                         }
641                 } else {
642                         src_page = pte_page(pteval);
643                         copy_user_highpage(page, src_page, address, vma);
644                         VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
645                         release_pte_page(src_page);
646                         /*
647                          * ptl mostly unnecessary, but preempt has to
648                          * be disabled to update the per-cpu stats
649                          * inside page_remove_rmap().
650                          */
651                         spin_lock(ptl);
652                         /*
653                          * paravirt calls inside pte_clear here are
654                          * superfluous.
655                          */
656                         pte_clear(vma->vm_mm, address, _pte);
657                         page_remove_rmap(src_page, false);
658                         spin_unlock(ptl);
659                         free_page_and_swap_cache(src_page);
660                 }
661         }
662 }
663 
664 static void khugepaged_alloc_sleep(void)
665 {
666         DEFINE_WAIT(wait);
667 
668         add_wait_queue(&khugepaged_wait, &wait);
669         freezable_schedule_timeout_interruptible(
670                 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
671         remove_wait_queue(&khugepaged_wait, &wait);
672 }
673 
674 static int khugepaged_node_load[MAX_NUMNODES];
675 
676 static bool khugepaged_scan_abort(int nid)
677 {
678         int i;
679 
680         /*
681          * If node_reclaim_mode is disabled, then no extra effort is made to
682          * allocate memory locally.
683          */
684         if (!node_reclaim_mode)
685                 return false;
686 
687         /* If there is a count for this node already, it must be acceptable */
688         if (khugepaged_node_load[nid])
689                 return false;
690 
691         for (i = 0; i < MAX_NUMNODES; i++) {
692                 if (!khugepaged_node_load[i])
693                         continue;
694                 if (node_distance(nid, i) > RECLAIM_DISTANCE)
695                         return true;
696         }
697         return false;
698 }
699 
700 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
701 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
702 {
703         return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
704 }
705 
706 #ifdef CONFIG_NUMA
707 static int khugepaged_find_target_node(void)
708 {
709         static int last_khugepaged_target_node = NUMA_NO_NODE;
710         int nid, target_node = 0, max_value = 0;
711 
712         /* find first node with max normal pages hit */
713         for (nid = 0; nid < MAX_NUMNODES; nid++)
714                 if (khugepaged_node_load[nid] > max_value) {
715                         max_value = khugepaged_node_load[nid];
716                         target_node = nid;
717                 }
718 
719         /* do some balance if several nodes have the same hit record */
720         if (target_node <= last_khugepaged_target_node)
721                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
722                                 nid++)
723                         if (max_value == khugepaged_node_load[nid]) {
724                                 target_node = nid;
725                                 break;
726                         }
727 
728         last_khugepaged_target_node = target_node;
729         return target_node;
730 }
731 
732 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
733 {
734         if (IS_ERR(*hpage)) {
735                 if (!*wait)
736                         return false;
737 
738                 *wait = false;
739                 *hpage = NULL;
740                 khugepaged_alloc_sleep();
741         } else if (*hpage) {
742                 put_page(*hpage);
743                 *hpage = NULL;
744         }
745 
746         return true;
747 }
748 
749 static struct page *
750 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
751 {
752         VM_BUG_ON_PAGE(*hpage, *hpage);
753 
754         *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
755         if (unlikely(!*hpage)) {
756                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
757                 *hpage = ERR_PTR(-ENOMEM);
758                 return NULL;
759         }
760 
761         prep_transhuge_page(*hpage);
762         count_vm_event(THP_COLLAPSE_ALLOC);
763         return *hpage;
764 }
765 #else
766 static int khugepaged_find_target_node(void)
767 {
768         return 0;
769 }
770 
771 static inline struct page *alloc_khugepaged_hugepage(void)
772 {
773         struct page *page;
774 
775         page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
776                            HPAGE_PMD_ORDER);
777         if (page)
778                 prep_transhuge_page(page);
779         return page;
780 }
781 
782 static struct page *khugepaged_alloc_hugepage(bool *wait)
783 {
784         struct page *hpage;
785 
786         do {
787                 hpage = alloc_khugepaged_hugepage();
788                 if (!hpage) {
789                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
790                         if (!*wait)
791                                 return NULL;
792 
793                         *wait = false;
794                         khugepaged_alloc_sleep();
795                 } else
796                         count_vm_event(THP_COLLAPSE_ALLOC);
797         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
798 
799         return hpage;
800 }
801 
802 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
803 {
804         if (!*hpage)
805                 *hpage = khugepaged_alloc_hugepage(wait);
806 
807         if (unlikely(!*hpage))
808                 return false;
809 
810         return true;
811 }
812 
813 static struct page *
814 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
815 {
816         VM_BUG_ON(!*hpage);
817 
818         return  *hpage;
819 }
820 #endif
821 
822 static bool hugepage_vma_check(struct vm_area_struct *vma)
823 {
824         if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
825             (vma->vm_flags & VM_NOHUGEPAGE) ||
826             test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
827                 return false;
828         if (shmem_file(vma->vm_file)) {
829                 if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
830                         return false;
831                 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
832                                 HPAGE_PMD_NR);
833         }
834         if (!vma->anon_vma || vma->vm_ops)
835                 return false;
836         if (is_vma_temporary_stack(vma))
837                 return false;
838         return !(vma->vm_flags & VM_NO_KHUGEPAGED);
839 }
840 
841 /*
842  * If mmap_sem temporarily dropped, revalidate vma
843  * before taking mmap_sem.
844  * Return 0 if succeeds, otherwise return none-zero
845  * value (scan code).
846  */
847 
848 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
849                 struct vm_area_struct **vmap)
850 {
851         struct vm_area_struct *vma;
852         unsigned long hstart, hend;
853 
854         if (unlikely(khugepaged_test_exit(mm)))
855                 return SCAN_ANY_PROCESS;
856 
857         *vmap = vma = find_vma(mm, address);
858         if (!vma)
859                 return SCAN_VMA_NULL;
860 
861         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
862         hend = vma->vm_end & HPAGE_PMD_MASK;
863         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
864                 return SCAN_ADDRESS_RANGE;
865         if (!hugepage_vma_check(vma))
866                 return SCAN_VMA_CHECK;
867         return 0;
868 }
869 
870 /*
871  * Bring missing pages in from swap, to complete THP collapse.
872  * Only done if khugepaged_scan_pmd believes it is worthwhile.
873  *
874  * Called and returns without pte mapped or spinlocks held,
875  * but with mmap_sem held to protect against vma changes.
876  */
877 
878 static bool __collapse_huge_page_swapin(struct mm_struct *mm,
879                                         struct vm_area_struct *vma,
880                                         unsigned long address, pmd_t *pmd,
881                                         int referenced)
882 {
883         int swapped_in = 0, ret = 0;
884         struct vm_fault vmf = {
885                 .vma = vma,
886                 .address = address,
887                 .flags = FAULT_FLAG_ALLOW_RETRY,
888                 .pmd = pmd,
889                 .pgoff = linear_page_index(vma, address),
890         };
891 
892         /* we only decide to swapin, if there is enough young ptes */
893         if (referenced < HPAGE_PMD_NR/2) {
894                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
895                 return false;
896         }
897         vmf.pte = pte_offset_map(pmd, address);
898         for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
899                         vmf.pte++, vmf.address += PAGE_SIZE) {
900                 vmf.orig_pte = *vmf.pte;
901                 if (!is_swap_pte(vmf.orig_pte))
902                         continue;
903                 swapped_in++;
904                 ret = do_swap_page(&vmf);
905 
906                 /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
907                 if (ret & VM_FAULT_RETRY) {
908                         down_read(&mm->mmap_sem);
909                         if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
910                                 /* vma is no longer available, don't continue to swapin */
911                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
912                                 return false;
913                         }
914                         /* check if the pmd is still valid */
915                         if (mm_find_pmd(mm, address) != pmd) {
916                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
917                                 return false;
918                         }
919                 }
920                 if (ret & VM_FAULT_ERROR) {
921                         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
922                         return false;
923                 }
924                 /* pte is unmapped now, we need to map it */
925                 vmf.pte = pte_offset_map(pmd, vmf.address);
926         }
927         vmf.pte--;
928         pte_unmap(vmf.pte);
929         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
930         return true;
931 }
932 
933 static void collapse_huge_page(struct mm_struct *mm,
934                                    unsigned long address,
935                                    struct page **hpage,
936                                    int node, int referenced)
937 {
938         pmd_t *pmd, _pmd;
939         pte_t *pte;
940         pgtable_t pgtable;
941         struct page *new_page;
942         spinlock_t *pmd_ptl, *pte_ptl;
943         int isolated = 0, result = 0;
944         struct mem_cgroup *memcg;
945         struct vm_area_struct *vma;
946         unsigned long mmun_start;       /* For mmu_notifiers */
947         unsigned long mmun_end;         /* For mmu_notifiers */
948         gfp_t gfp;
949 
950         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
951 
952         /* Only allocate from the target node */
953         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
954 
955         /*
956          * Before allocating the hugepage, release the mmap_sem read lock.
957          * The allocation can take potentially a long time if it involves
958          * sync compaction, and we do not need to hold the mmap_sem during
959          * that. We will recheck the vma after taking it again in write mode.
960          */
961         up_read(&mm->mmap_sem);
962         new_page = khugepaged_alloc_page(hpage, gfp, node);
963         if (!new_page) {
964                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
965                 goto out_nolock;
966         }
967 
968         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
969                 result = SCAN_CGROUP_CHARGE_FAIL;
970                 goto out_nolock;
971         }
972 
973         down_read(&mm->mmap_sem);
974         result = hugepage_vma_revalidate(mm, address, &vma);
975         if (result) {
976                 mem_cgroup_cancel_charge(new_page, memcg, true);
977                 up_read(&mm->mmap_sem);
978                 goto out_nolock;
979         }
980 
981         pmd = mm_find_pmd(mm, address);
982         if (!pmd) {
983                 result = SCAN_PMD_NULL;
984                 mem_cgroup_cancel_charge(new_page, memcg, true);
985                 up_read(&mm->mmap_sem);
986                 goto out_nolock;
987         }
988 
989         /*
990          * __collapse_huge_page_swapin always returns with mmap_sem locked.
991          * If it fails, we release mmap_sem and jump out_nolock.
992          * Continuing to collapse causes inconsistency.
993          */
994         if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) {
995                 mem_cgroup_cancel_charge(new_page, memcg, true);
996                 up_read(&mm->mmap_sem);
997                 goto out_nolock;
998         }
999 
1000         up_read(&mm->mmap_sem);
1001         /*
1002          * Prevent all access to pagetables with the exception of
1003          * gup_fast later handled by the ptep_clear_flush and the VM
1004          * handled by the anon_vma lock + PG_lock.
1005          */
1006         down_write(&mm->mmap_sem);
1007         result = hugepage_vma_revalidate(mm, address, &vma);
1008         if (result)
1009                 goto out;
1010         /* check if the pmd is still valid */
1011         if (mm_find_pmd(mm, address) != pmd)
1012                 goto out;
1013 
1014         anon_vma_lock_write(vma->anon_vma);
1015 
1016         pte = pte_offset_map(pmd, address);
1017         pte_ptl = pte_lockptr(mm, pmd);
1018 
1019         mmun_start = address;
1020         mmun_end   = address + HPAGE_PMD_SIZE;
1021         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1022         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1023         /*
1024          * After this gup_fast can't run anymore. This also removes
1025          * any huge TLB entry from the CPU so we won't allow
1026          * huge and small TLB entries for the same virtual address
1027          * to avoid the risk of CPU bugs in that area.
1028          */
1029         _pmd = pmdp_collapse_flush(vma, address, pmd);
1030         spin_unlock(pmd_ptl);
1031         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1032 
1033         spin_lock(pte_ptl);
1034         isolated = __collapse_huge_page_isolate(vma, address, pte);
1035         spin_unlock(pte_ptl);
1036 
1037         if (unlikely(!isolated)) {
1038                 pte_unmap(pte);
1039                 spin_lock(pmd_ptl);
1040                 BUG_ON(!pmd_none(*pmd));
1041                 /*
1042                  * We can only use set_pmd_at when establishing
1043                  * hugepmds and never for establishing regular pmds that
1044                  * points to regular pagetables. Use pmd_populate for that
1045                  */
1046                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1047                 spin_unlock(pmd_ptl);
1048                 anon_vma_unlock_write(vma->anon_vma);
1049                 result = SCAN_FAIL;
1050                 goto out;
1051         }
1052 
1053         /*
1054          * All pages are isolated and locked so anon_vma rmap
1055          * can't run anymore.
1056          */
1057         anon_vma_unlock_write(vma->anon_vma);
1058 
1059         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
1060         pte_unmap(pte);
1061         __SetPageUptodate(new_page);
1062         pgtable = pmd_pgtable(_pmd);
1063 
1064         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1065         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1066 
1067         /*
1068          * spin_lock() below is not the equivalent of smp_wmb(), so
1069          * this is needed to avoid the copy_huge_page writes to become
1070          * visible after the set_pmd_at() write.
1071          */
1072         smp_wmb();
1073 
1074         spin_lock(pmd_ptl);
1075         BUG_ON(!pmd_none(*pmd));
1076         page_add_new_anon_rmap(new_page, vma, address, true);
1077         mem_cgroup_commit_charge(new_page, memcg, false, true);
1078         lru_cache_add_active_or_unevictable(new_page, vma);
1079         pgtable_trans_huge_deposit(mm, pmd, pgtable);
1080         set_pmd_at(mm, address, pmd, _pmd);
1081         update_mmu_cache_pmd(vma, address, pmd);
1082         spin_unlock(pmd_ptl);
1083 
1084         *hpage = NULL;
1085 
1086         khugepaged_pages_collapsed++;
1087         result = SCAN_SUCCEED;
1088 out_up_write:
1089         up_write(&mm->mmap_sem);
1090 out_nolock:
1091         trace_mm_collapse_huge_page(mm, isolated, result);
1092         return;
1093 out:
1094         mem_cgroup_cancel_charge(new_page, memcg, true);
1095         goto out_up_write;
1096 }
1097 
1098 static int khugepaged_scan_pmd(struct mm_struct *mm,
1099                                struct vm_area_struct *vma,
1100                                unsigned long address,
1101                                struct page **hpage)
1102 {
1103         pmd_t *pmd;
1104         pte_t *pte, *_pte;
1105         int ret = 0, none_or_zero = 0, result = 0, referenced = 0;
1106         struct page *page = NULL;
1107         unsigned long _address;
1108         spinlock_t *ptl;
1109         int node = NUMA_NO_NODE, unmapped = 0;
1110         bool writable = false;
1111 
1112         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1113 
1114         pmd = mm_find_pmd(mm, address);
1115         if (!pmd) {
1116                 result = SCAN_PMD_NULL;
1117                 goto out;
1118         }
1119 
1120         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1121         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1122         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1123              _pte++, _address += PAGE_SIZE) {
1124                 pte_t pteval = *_pte;
1125                 if (is_swap_pte(pteval)) {
1126                         if (++unmapped <= khugepaged_max_ptes_swap) {
1127                                 continue;
1128                         } else {
1129                                 result = SCAN_EXCEED_SWAP_PTE;
1130                                 goto out_unmap;
1131                         }
1132                 }
1133                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1134                         if (!userfaultfd_armed(vma) &&
1135                             ++none_or_zero <= khugepaged_max_ptes_none) {
1136                                 continue;
1137                         } else {
1138                                 result = SCAN_EXCEED_NONE_PTE;
1139                                 goto out_unmap;
1140                         }
1141                 }
1142                 if (!pte_present(pteval)) {
1143                         result = SCAN_PTE_NON_PRESENT;
1144                         goto out_unmap;
1145                 }
1146                 if (pte_write(pteval))
1147                         writable = true;
1148 
1149                 page = vm_normal_page(vma, _address, pteval);
1150                 if (unlikely(!page)) {
1151                         result = SCAN_PAGE_NULL;
1152                         goto out_unmap;
1153                 }
1154 
1155                 /* TODO: teach khugepaged to collapse THP mapped with pte */
1156                 if (PageCompound(page)) {
1157                         result = SCAN_PAGE_COMPOUND;
1158                         goto out_unmap;
1159                 }
1160 
1161                 /*
1162                  * Record which node the original page is from and save this
1163                  * information to khugepaged_node_load[].
1164                  * Khupaged will allocate hugepage from the node has the max
1165                  * hit record.
1166                  */
1167                 node = page_to_nid(page);
1168                 if (khugepaged_scan_abort(node)) {
1169                         result = SCAN_SCAN_ABORT;
1170                         goto out_unmap;
1171                 }
1172                 khugepaged_node_load[node]++;
1173                 if (!PageLRU(page)) {
1174                         result = SCAN_PAGE_LRU;
1175                         goto out_unmap;
1176                 }
1177                 if (PageLocked(page)) {
1178                         result = SCAN_PAGE_LOCK;
1179                         goto out_unmap;
1180                 }
1181                 if (!PageAnon(page)) {
1182                         result = SCAN_PAGE_ANON;
1183                         goto out_unmap;
1184                 }
1185 
1186                 /*
1187                  * cannot use mapcount: can't collapse if there's a gup pin.
1188                  * The page must only be referenced by the scanned process
1189                  * and page swap cache.
1190                  */
1191                 if (page_count(page) != 1 + PageSwapCache(page)) {
1192                         result = SCAN_PAGE_COUNT;
1193                         goto out_unmap;
1194                 }
1195                 if (pte_young(pteval) ||
1196                     page_is_young(page) || PageReferenced(page) ||
1197                     mmu_notifier_test_young(vma->vm_mm, address))
1198                         referenced++;
1199         }
1200         if (writable) {
1201                 if (referenced) {
1202                         result = SCAN_SUCCEED;
1203                         ret = 1;
1204                 } else {
1205                         result = SCAN_LACK_REFERENCED_PAGE;
1206                 }
1207         } else {
1208                 result = SCAN_PAGE_RO;
1209         }
1210 out_unmap:
1211         pte_unmap_unlock(pte, ptl);
1212         if (ret) {
1213                 node = khugepaged_find_target_node();
1214                 /* collapse_huge_page will return with the mmap_sem released */
1215                 collapse_huge_page(mm, address, hpage, node, referenced);
1216         }
1217 out:
1218         trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1219                                      none_or_zero, result, unmapped);
1220         return ret;
1221 }
1222 
1223 static void collect_mm_slot(struct mm_slot *mm_slot)
1224 {
1225         struct mm_struct *mm = mm_slot->mm;
1226 
1227         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
1228 
1229         if (khugepaged_test_exit(mm)) {
1230                 /* free mm_slot */
1231                 hash_del(&mm_slot->hash);
1232                 list_del(&mm_slot->mm_node);
1233 
1234                 /*
1235                  * Not strictly needed because the mm exited already.
1236                  *
1237                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1238                  */
1239 
1240                 /* khugepaged_mm_lock actually not necessary for the below */
1241                 free_mm_slot(mm_slot);
1242                 mmdrop(mm);
1243         }
1244 }
1245 
1246 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
1247 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1248 {
1249         struct vm_area_struct *vma;
1250         unsigned long addr;
1251         pmd_t *pmd, _pmd;
1252 
1253         i_mmap_lock_write(mapping);
1254         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1255                 /* probably overkill */
1256                 if (vma->anon_vma)
1257                         continue;
1258                 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1259                 if (addr & ~HPAGE_PMD_MASK)
1260                         continue;
1261                 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1262                         continue;
1263                 pmd = mm_find_pmd(vma->vm_mm, addr);
1264                 if (!pmd)
1265                         continue;
1266                 /*
1267                  * We need exclusive mmap_sem to retract page table.
1268                  * If trylock fails we would end up with pte-mapped THP after
1269                  * re-fault. Not ideal, but it's more important to not disturb
1270                  * the system too much.
1271                  */
1272                 if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
1273                         spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
1274                         /* assume page table is clear */
1275                         _pmd = pmdp_collapse_flush(vma, addr, pmd);
1276                         spin_unlock(ptl);
1277                         up_write(&vma->vm_mm->mmap_sem);
1278                         mm_dec_nr_ptes(vma->vm_mm);
1279                         pte_free(vma->vm_mm, pmd_pgtable(_pmd));
1280                 }
1281         }
1282         i_mmap_unlock_write(mapping);
1283 }
1284 
1285 /**
1286  * collapse_shmem - collapse small tmpfs/shmem pages into huge one.
1287  *
1288  * Basic scheme is simple, details are more complex:
1289  *  - allocate and freeze a new huge page;
1290  *  - scan over radix tree replacing old pages the new one
1291  *    + swap in pages if necessary;
1292  *    + fill in gaps;
1293  *    + keep old pages around in case if rollback is required;
1294  *  - if replacing succeed:
1295  *    + copy data over;
1296  *    + free old pages;
1297  *    + unfreeze huge page;
1298  *  - if replacing failed;
1299  *    + put all pages back and unfreeze them;
1300  *    + restore gaps in the radix-tree;
1301  *    + free huge page;
1302  */
1303 static void collapse_shmem(struct mm_struct *mm,
1304                 struct address_space *mapping, pgoff_t start,
1305                 struct page **hpage, int node)
1306 {
1307         gfp_t gfp;
1308         struct page *page, *new_page, *tmp;
1309         struct mem_cgroup *memcg;
1310         pgoff_t index, end = start + HPAGE_PMD_NR;
1311         LIST_HEAD(pagelist);
1312         struct radix_tree_iter iter;
1313         void **slot;
1314         int nr_none = 0, result = SCAN_SUCCEED;
1315 
1316         VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1317 
1318         /* Only allocate from the target node */
1319         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1320 
1321         new_page = khugepaged_alloc_page(hpage, gfp, node);
1322         if (!new_page) {
1323                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1324                 goto out;
1325         }
1326 
1327         if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
1328                 result = SCAN_CGROUP_CHARGE_FAIL;
1329                 goto out;
1330         }
1331 
1332         new_page->index = start;
1333         new_page->mapping = mapping;
1334         __SetPageSwapBacked(new_page);
1335         __SetPageLocked(new_page);
1336         BUG_ON(!page_ref_freeze(new_page, 1));
1337 
1338 
1339         /*
1340          * At this point the new_page is 'frozen' (page_count() is zero), locked
1341          * and not up-to-date. It's safe to insert it into radix tree, because
1342          * nobody would be able to map it or use it in other way until we
1343          * unfreeze it.
1344          */
1345 
1346         index = start;
1347         xa_lock_irq(&mapping->i_pages);
1348         radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start) {
1349                 int n = min(iter.index, end) - index;
1350 
1351                 /*
1352                  * Handle holes in the radix tree: charge it from shmem and
1353                  * insert relevant subpage of new_page into the radix-tree.
1354                  */
1355                 if (n && !shmem_charge(mapping->host, n)) {
1356                         result = SCAN_FAIL;
1357                         break;
1358                 }
1359                 nr_none += n;
1360                 for (; index < min(iter.index, end); index++) {
1361                         radix_tree_insert(&mapping->i_pages, index,
1362                                         new_page + (index % HPAGE_PMD_NR));
1363                 }
1364 
1365                 /* We are done. */
1366                 if (index >= end)
1367                         break;
1368 
1369                 page = radix_tree_deref_slot_protected(slot,
1370                                 &mapping->i_pages.xa_lock);
1371                 if (radix_tree_exceptional_entry(page) || !PageUptodate(page)) {
1372                         xa_unlock_irq(&mapping->i_pages);
1373                         /* swap in or instantiate fallocated page */
1374                         if (shmem_getpage(mapping->host, index, &page,
1375                                                 SGP_NOHUGE)) {
1376                                 result = SCAN_FAIL;
1377                                 goto tree_unlocked;
1378                         }
1379                         xa_lock_irq(&mapping->i_pages);
1380                 } else if (trylock_page(page)) {
1381                         get_page(page);
1382                 } else {
1383                         result = SCAN_PAGE_LOCK;
1384                         break;
1385                 }
1386 
1387                 /*
1388                  * The page must be locked, so we can drop the i_pages lock
1389                  * without racing with truncate.
1390                  */
1391                 VM_BUG_ON_PAGE(!PageLocked(page), page);
1392                 VM_BUG_ON_PAGE(!PageUptodate(page), page);
1393                 VM_BUG_ON_PAGE(PageTransCompound(page), page);
1394 
1395                 if (page_mapping(page) != mapping) {
1396                         result = SCAN_TRUNCATED;
1397                         goto out_unlock;
1398                 }
1399                 xa_unlock_irq(&mapping->i_pages);
1400 
1401                 if (isolate_lru_page(page)) {
1402                         result = SCAN_DEL_PAGE_LRU;
1403                         goto out_isolate_failed;
1404                 }
1405 
1406                 if (page_mapped(page))
1407                         unmap_mapping_pages(mapping, index, 1, false);
1408 
1409                 xa_lock_irq(&mapping->i_pages);
1410 
1411                 slot = radix_tree_lookup_slot(&mapping->i_pages, index);
1412                 VM_BUG_ON_PAGE(page != radix_tree_deref_slot_protected(slot,
1413                                         &mapping->i_pages.xa_lock), page);
1414                 VM_BUG_ON_PAGE(page_mapped(page), page);
1415 
1416                 /*
1417                  * The page is expected to have page_count() == 3:
1418                  *  - we hold a pin on it;
1419                  *  - one reference from radix tree;
1420                  *  - one from isolate_lru_page;
1421                  */
1422                 if (!page_ref_freeze(page, 3)) {
1423                         result = SCAN_PAGE_COUNT;
1424                         goto out_lru;
1425                 }
1426 
1427                 /*
1428                  * Add the page to the list to be able to undo the collapse if
1429                  * something go wrong.
1430                  */
1431                 list_add_tail(&page->lru, &pagelist);
1432 
1433                 /* Finally, replace with the new page. */
1434                 radix_tree_replace_slot(&mapping->i_pages, slot,
1435                                 new_page + (index % HPAGE_PMD_NR));
1436 
1437                 slot = radix_tree_iter_resume(slot, &iter);
1438                 index++;
1439                 continue;
1440 out_lru:
1441                 xa_unlock_irq(&mapping->i_pages);
1442                 putback_lru_page(page);
1443 out_isolate_failed:
1444                 unlock_page(page);
1445                 put_page(page);
1446                 goto tree_unlocked;
1447 out_unlock:
1448                 unlock_page(page);
1449                 put_page(page);
1450                 break;
1451         }
1452 
1453         /*
1454          * Handle hole in radix tree at the end of the range.
1455          * This code only triggers if there's nothing in radix tree
1456          * beyond 'end'.
1457          */
1458         if (result == SCAN_SUCCEED && index < end) {
1459                 int n = end - index;
1460 
1461                 if (!shmem_charge(mapping->host, n)) {
1462                         result = SCAN_FAIL;
1463                         goto tree_locked;
1464                 }
1465 
1466                 for (; index < end; index++) {
1467                         radix_tree_insert(&mapping->i_pages, index,
1468                                         new_page + (index % HPAGE_PMD_NR));
1469                 }
1470                 nr_none += n;
1471         }
1472 
1473 tree_locked:
1474         xa_unlock_irq(&mapping->i_pages);
1475 tree_unlocked:
1476 
1477         if (result == SCAN_SUCCEED) {
1478                 unsigned long flags;
1479                 struct zone *zone = page_zone(new_page);
1480 
1481                 /*
1482                  * Replacing old pages with new one has succeed, now we need to
1483                  * copy the content and free old pages.
1484                  */
1485                 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1486                         copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1487                                         page);
1488                         list_del(&page->lru);
1489                         unlock_page(page);
1490                         page_ref_unfreeze(page, 1);
1491                         page->mapping = NULL;
1492                         ClearPageActive(page);
1493                         ClearPageUnevictable(page);
1494                         put_page(page);
1495                 }
1496 
1497                 local_irq_save(flags);
1498                 __inc_node_page_state(new_page, NR_SHMEM_THPS);
1499                 if (nr_none) {
1500                         __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
1501                         __mod_node_page_state(zone->zone_pgdat, NR_SHMEM, nr_none);
1502                 }
1503                 local_irq_restore(flags);
1504 
1505                 /*
1506                  * Remove pte page tables, so we can re-faulti
1507                  * the page as huge.
1508                  */
1509                 retract_page_tables(mapping, start);
1510 
1511                 /* Everything is ready, let's unfreeze the new_page */
1512                 set_page_dirty(new_page);
1513                 SetPageUptodate(new_page);
1514                 page_ref_unfreeze(new_page, HPAGE_PMD_NR);
1515                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1516                 lru_cache_add_anon(new_page);
1517                 unlock_page(new_page);
1518 
1519                 *hpage = NULL;
1520         } else {
1521                 /* Something went wrong: rollback changes to the radix-tree */
1522                 shmem_uncharge(mapping->host, nr_none);
1523                 xa_lock_irq(&mapping->i_pages);
1524                 radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start) {
1525                         if (iter.index >= end)
1526                                 break;
1527                         page = list_first_entry_or_null(&pagelist,
1528                                         struct page, lru);
1529                         if (!page || iter.index < page->index) {
1530                                 if (!nr_none)
1531                                         break;
1532                                 nr_none--;
1533                                 /* Put holes back where they were */
1534                                 radix_tree_delete(&mapping->i_pages, iter.index);
1535                                 continue;
1536                         }
1537 
1538                         VM_BUG_ON_PAGE(page->index != iter.index, page);
1539 
1540                         /* Unfreeze the page. */
1541                         list_del(&page->lru);
1542                         page_ref_unfreeze(page, 2);
1543                         radix_tree_replace_slot(&mapping->i_pages, slot, page);
1544                         slot = radix_tree_iter_resume(slot, &iter);
1545                         xa_unlock_irq(&mapping->i_pages);
1546                         putback_lru_page(page);
1547                         unlock_page(page);
1548                         xa_lock_irq(&mapping->i_pages);
1549                 }
1550                 VM_BUG_ON(nr_none);
1551                 xa_unlock_irq(&mapping->i_pages);
1552 
1553                 /* Unfreeze new_page, caller would take care about freeing it */
1554                 page_ref_unfreeze(new_page, 1);
1555                 mem_cgroup_cancel_charge(new_page, memcg, true);
1556                 unlock_page(new_page);
1557                 new_page->mapping = NULL;
1558         }
1559 out:
1560         VM_BUG_ON(!list_empty(&pagelist));
1561         /* TODO: tracepoints */
1562 }
1563 
1564 static void khugepaged_scan_shmem(struct mm_struct *mm,
1565                 struct address_space *mapping,
1566                 pgoff_t start, struct page **hpage)
1567 {
1568         struct page *page = NULL;
1569         struct radix_tree_iter iter;
1570         void **slot;
1571         int present, swap;
1572         int node = NUMA_NO_NODE;
1573         int result = SCAN_SUCCEED;
1574 
1575         present = 0;
1576         swap = 0;
1577         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1578         rcu_read_lock();
1579         radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start) {
1580                 if (iter.index >= start + HPAGE_PMD_NR)
1581                         break;
1582 
1583                 page = radix_tree_deref_slot(slot);
1584                 if (radix_tree_deref_retry(page)) {
1585                         slot = radix_tree_iter_retry(&iter);
1586                         continue;
1587                 }
1588 
1589                 if (radix_tree_exception(page)) {
1590                         if (++swap > khugepaged_max_ptes_swap) {
1591                                 result = SCAN_EXCEED_SWAP_PTE;
1592                                 break;
1593                         }
1594                         continue;
1595                 }
1596 
1597                 if (PageTransCompound(page)) {
1598                         result = SCAN_PAGE_COMPOUND;
1599                         break;
1600                 }
1601 
1602                 node = page_to_nid(page);
1603                 if (khugepaged_scan_abort(node)) {
1604                         result = SCAN_SCAN_ABORT;
1605                         break;
1606                 }
1607                 khugepaged_node_load[node]++;
1608 
1609                 if (!PageLRU(page)) {
1610                         result = SCAN_PAGE_LRU;
1611                         break;
1612                 }
1613 
1614                 if (page_count(page) != 1 + page_mapcount(page)) {
1615                         result = SCAN_PAGE_COUNT;
1616                         break;
1617                 }
1618 
1619                 /*
1620                  * We probably should check if the page is referenced here, but
1621                  * nobody would transfer pte_young() to PageReferenced() for us.
1622                  * And rmap walk here is just too costly...
1623                  */
1624 
1625                 present++;
1626 
1627                 if (need_resched()) {
1628                         slot = radix_tree_iter_resume(slot, &iter);
1629                         cond_resched_rcu();
1630                 }
1631         }
1632         rcu_read_unlock();
1633 
1634         if (result == SCAN_SUCCEED) {
1635                 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
1636                         result = SCAN_EXCEED_NONE_PTE;
1637                 } else {
1638                         node = khugepaged_find_target_node();
1639                         collapse_shmem(mm, mapping, start, hpage, node);
1640                 }
1641         }
1642 
1643         /* TODO: tracepoints */
1644 }
1645 #else
1646 static void khugepaged_scan_shmem(struct mm_struct *mm,
1647                 struct address_space *mapping,
1648                 pgoff_t start, struct page **hpage)
1649 {
1650         BUILD_BUG();
1651 }
1652 #endif
1653 
1654 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
1655                                             struct page **hpage)
1656         __releases(&khugepaged_mm_lock)
1657         __acquires(&khugepaged_mm_lock)
1658 {
1659         struct mm_slot *mm_slot;
1660         struct mm_struct *mm;
1661         struct vm_area_struct *vma;
1662         int progress = 0;
1663 
1664         VM_BUG_ON(!pages);
1665         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
1666 
1667         if (khugepaged_scan.mm_slot)
1668                 mm_slot = khugepaged_scan.mm_slot;
1669         else {
1670                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
1671                                      struct mm_slot, mm_node);
1672                 khugepaged_scan.address = 0;
1673                 khugepaged_scan.mm_slot = mm_slot;
1674         }
1675         spin_unlock(&khugepaged_mm_lock);
1676 
1677         mm = mm_slot->mm;
1678         /*
1679          * Don't wait for semaphore (to avoid long wait times).  Just move to
1680          * the next mm on the list.
1681          */
1682         vma = NULL;
1683         if (unlikely(!down_read_trylock(&mm->mmap_sem)))
1684                 goto breakouterloop_mmap_sem;
1685         if (likely(!khugepaged_test_exit(mm)))
1686                 vma = find_vma(mm, khugepaged_scan.address);
1687 
1688         progress++;
1689         for (; vma; vma = vma->vm_next) {
1690                 unsigned long hstart, hend;
1691 
1692                 cond_resched();
1693                 if (unlikely(khugepaged_test_exit(mm))) {
1694                         progress++;
1695                         break;
1696                 }
1697                 if (!hugepage_vma_check(vma)) {
1698 skip:
1699                         progress++;
1700                         continue;
1701                 }
1702                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1703                 hend = vma->vm_end & HPAGE_PMD_MASK;
1704                 if (hstart >= hend)
1705                         goto skip;
1706                 if (khugepaged_scan.address > hend)
1707                         goto skip;
1708                 if (khugepaged_scan.address < hstart)
1709                         khugepaged_scan.address = hstart;
1710                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
1711 
1712                 while (khugepaged_scan.address < hend) {
1713                         int ret;
1714                         cond_resched();
1715                         if (unlikely(khugepaged_test_exit(mm)))
1716                                 goto breakouterloop;
1717 
1718                         VM_BUG_ON(khugepaged_scan.address < hstart ||
1719                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
1720                                   hend);
1721                         if (shmem_file(vma->vm_file)) {
1722                                 struct file *file;
1723                                 pgoff_t pgoff = linear_page_index(vma,
1724                                                 khugepaged_scan.address);
1725                                 if (!shmem_huge_enabled(vma))
1726                                         goto skip;
1727                                 file = get_file(vma->vm_file);
1728                                 up_read(&mm->mmap_sem);
1729                                 ret = 1;
1730                                 khugepaged_scan_shmem(mm, file->f_mapping,
1731                                                 pgoff, hpage);
1732                                 fput(file);
1733                         } else {
1734                                 ret = khugepaged_scan_pmd(mm, vma,
1735                                                 khugepaged_scan.address,
1736                                                 hpage);
1737                         }
1738                         /* move to next address */
1739                         khugepaged_scan.address += HPAGE_PMD_SIZE;
1740                         progress += HPAGE_PMD_NR;
1741                         if (ret)
1742                                 /* we released mmap_sem so break loop */
1743                                 goto breakouterloop_mmap_sem;
1744                         if (progress >= pages)
1745                                 goto breakouterloop;
1746                 }
1747         }
1748 breakouterloop:
1749         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
1750 breakouterloop_mmap_sem:
1751 
1752         spin_lock(&khugepaged_mm_lock);
1753         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
1754         /*
1755          * Release the current mm_slot if this mm is about to die, or
1756          * if we scanned all vmas of this mm.
1757          */
1758         if (khugepaged_test_exit(mm) || !vma) {
1759                 /*
1760                  * Make sure that if mm_users is reaching zero while
1761                  * khugepaged runs here, khugepaged_exit will find
1762                  * mm_slot not pointing to the exiting mm.
1763                  */
1764                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
1765                         khugepaged_scan.mm_slot = list_entry(
1766                                 mm_slot->mm_node.next,
1767                                 struct mm_slot, mm_node);
1768                         khugepaged_scan.address = 0;
1769                 } else {
1770                         khugepaged_scan.mm_slot = NULL;
1771                         khugepaged_full_scans++;
1772                 }
1773 
1774                 collect_mm_slot(mm_slot);
1775         }
1776 
1777         return progress;
1778 }
1779 
1780 static int khugepaged_has_work(void)
1781 {
1782         return !list_empty(&khugepaged_scan.mm_head) &&
1783                 khugepaged_enabled();
1784 }
1785 
1786 static int khugepaged_wait_event(void)
1787 {
1788         return !list_empty(&khugepaged_scan.mm_head) ||
1789                 kthread_should_stop();
1790 }
1791 
1792 static void khugepaged_do_scan(void)
1793 {
1794         struct page *hpage = NULL;
1795         unsigned int progress = 0, pass_through_head = 0;
1796         unsigned int pages = khugepaged_pages_to_scan;
1797         bool wait = true;
1798 
1799         barrier(); /* write khugepaged_pages_to_scan to local stack */
1800 
1801         while (progress < pages) {
1802                 if (!khugepaged_prealloc_page(&hpage, &wait))
1803                         break;
1804 
1805                 cond_resched();
1806 
1807                 if (unlikely(kthread_should_stop() || try_to_freeze()))
1808                         break;
1809 
1810                 spin_lock(&khugepaged_mm_lock);
1811                 if (!khugepaged_scan.mm_slot)
1812                         pass_through_head++;
1813                 if (khugepaged_has_work() &&
1814                     pass_through_head < 2)
1815                         progress += khugepaged_scan_mm_slot(pages - progress,
1816                                                             &hpage);
1817                 else
1818                         progress = pages;
1819                 spin_unlock(&khugepaged_mm_lock);
1820         }
1821 
1822         if (!IS_ERR_OR_NULL(hpage))
1823                 put_page(hpage);
1824 }
1825 
1826 static bool khugepaged_should_wakeup(void)
1827 {
1828         return kthread_should_stop() ||
1829                time_after_eq(jiffies, khugepaged_sleep_expire);
1830 }
1831 
1832 static void khugepaged_wait_work(void)
1833 {
1834         if (khugepaged_has_work()) {
1835                 const unsigned long scan_sleep_jiffies =
1836                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
1837 
1838                 if (!scan_sleep_jiffies)
1839                         return;
1840 
1841                 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
1842                 wait_event_freezable_timeout(khugepaged_wait,
1843                                              khugepaged_should_wakeup(),
1844                                              scan_sleep_jiffies);
1845                 return;
1846         }
1847 
1848         if (khugepaged_enabled())
1849                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
1850 }
1851 
1852 static int khugepaged(void *none)
1853 {
1854         struct mm_slot *mm_slot;
1855 
1856         set_freezable();
1857         set_user_nice(current, MAX_NICE);
1858 
1859         while (!kthread_should_stop()) {
1860                 khugepaged_do_scan();
1861                 khugepaged_wait_work();
1862         }
1863 
1864         spin_lock(&khugepaged_mm_lock);
1865         mm_slot = khugepaged_scan.mm_slot;
1866         khugepaged_scan.mm_slot = NULL;
1867         if (mm_slot)
1868                 collect_mm_slot(mm_slot);
1869         spin_unlock(&khugepaged_mm_lock);
1870         return 0;
1871 }
1872 
1873 static void set_recommended_min_free_kbytes(void)
1874 {
1875         struct zone *zone;
1876         int nr_zones = 0;
1877         unsigned long recommended_min;
1878 
1879         for_each_populated_zone(zone) {
1880                 /*
1881                  * We don't need to worry about fragmentation of
1882                  * ZONE_MOVABLE since it only has movable pages.
1883                  */
1884                 if (zone_idx(zone) > gfp_zone(GFP_USER))
1885                         continue;
1886 
1887                 nr_zones++;
1888         }
1889 
1890         /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
1891         recommended_min = pageblock_nr_pages * nr_zones * 2;
1892 
1893         /*
1894          * Make sure that on average at least two pageblocks are almost free
1895          * of another type, one for a migratetype to fall back to and a
1896          * second to avoid subsequent fallbacks of other types There are 3
1897          * MIGRATE_TYPES we care about.
1898          */
1899         recommended_min += pageblock_nr_pages * nr_zones *
1900                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
1901 
1902         /* don't ever allow to reserve more than 5% of the lowmem */
1903         recommended_min = min(recommended_min,
1904                               (unsigned long) nr_free_buffer_pages() / 20);
1905         recommended_min <<= (PAGE_SHIFT-10);
1906 
1907         if (recommended_min > min_free_kbytes) {
1908                 if (user_min_free_kbytes >= 0)
1909                         pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
1910                                 min_free_kbytes, recommended_min);
1911 
1912                 min_free_kbytes = recommended_min;
1913         }
1914         setup_per_zone_wmarks();
1915 }
1916 
1917 int start_stop_khugepaged(void)
1918 {
1919         static struct task_struct *khugepaged_thread __read_mostly;
1920         static DEFINE_MUTEX(khugepaged_mutex);
1921         int err = 0;
1922 
1923         mutex_lock(&khugepaged_mutex);
1924         if (khugepaged_enabled()) {
1925                 if (!khugepaged_thread)
1926                         khugepaged_thread = kthread_run(khugepaged, NULL,
1927                                                         "khugepaged");
1928                 if (IS_ERR(khugepaged_thread)) {
1929                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
1930                         err = PTR_ERR(khugepaged_thread);
1931                         khugepaged_thread = NULL;
1932                         goto fail;
1933                 }
1934 
1935                 if (!list_empty(&khugepaged_scan.mm_head))
1936                         wake_up_interruptible(&khugepaged_wait);
1937 
1938                 set_recommended_min_free_kbytes();
1939         } else if (khugepaged_thread) {
1940                 kthread_stop(khugepaged_thread);
1941                 khugepaged_thread = NULL;
1942         }
1943 fail:
1944         mutex_unlock(&khugepaged_mutex);
1945         return err;
1946 }
1947 

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