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TOMOYO Linux Cross Reference
Linux/mm/swap_state.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  *  linux/mm/swap_state.c
  4  *
  5  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  6  *  Swap reorganised 29.12.95, Stephen Tweedie
  7  *
  8  *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
  9  */
 10 #include <linux/mm.h>
 11 #include <linux/gfp.h>
 12 #include <linux/kernel_stat.h>
 13 #include <linux/swap.h>
 14 #include <linux/swapops.h>
 15 #include <linux/init.h>
 16 #include <linux/pagemap.h>
 17 #include <linux/backing-dev.h>
 18 #include <linux/blkdev.h>
 19 #include <linux/pagevec.h>
 20 #include <linux/migrate.h>
 21 #include <linux/vmalloc.h>
 22 #include <linux/swap_slots.h>
 23 #include <linux/huge_mm.h>
 24 
 25 #include <asm/pgtable.h>
 26 
 27 /*
 28  * swapper_space is a fiction, retained to simplify the path through
 29  * vmscan's shrink_page_list.
 30  */
 31 static const struct address_space_operations swap_aops = {
 32         .writepage      = swap_writepage,
 33         .set_page_dirty = swap_set_page_dirty,
 34 #ifdef CONFIG_MIGRATION
 35         .migratepage    = migrate_page,
 36 #endif
 37 };
 38 
 39 struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
 40 static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
 41 bool swap_vma_readahead __read_mostly = true;
 42 
 43 #define SWAP_RA_WIN_SHIFT       (PAGE_SHIFT / 2)
 44 #define SWAP_RA_HITS_MASK       ((1UL << SWAP_RA_WIN_SHIFT) - 1)
 45 #define SWAP_RA_HITS_MAX        SWAP_RA_HITS_MASK
 46 #define SWAP_RA_WIN_MASK        (~PAGE_MASK & ~SWAP_RA_HITS_MASK)
 47 
 48 #define SWAP_RA_HITS(v)         ((v) & SWAP_RA_HITS_MASK)
 49 #define SWAP_RA_WIN(v)          (((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT)
 50 #define SWAP_RA_ADDR(v)         ((v) & PAGE_MASK)
 51 
 52 #define SWAP_RA_VAL(addr, win, hits)                            \
 53         (((addr) & PAGE_MASK) |                                 \
 54          (((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) |    \
 55          ((hits) & SWAP_RA_HITS_MASK))
 56 
 57 /* Initial readahead hits is 4 to start up with a small window */
 58 #define GET_SWAP_RA_VAL(vma)                                    \
 59         (atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
 60 
 61 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
 62 #define ADD_CACHE_INFO(x, nr)   do { swap_cache_info.x += (nr); } while (0)
 63 
 64 static struct {
 65         unsigned long add_total;
 66         unsigned long del_total;
 67         unsigned long find_success;
 68         unsigned long find_total;
 69 } swap_cache_info;
 70 
 71 unsigned long total_swapcache_pages(void)
 72 {
 73         unsigned int i, j, nr;
 74         unsigned long ret = 0;
 75         struct address_space *spaces;
 76 
 77         rcu_read_lock();
 78         for (i = 0; i < MAX_SWAPFILES; i++) {
 79                 /*
 80                  * The corresponding entries in nr_swapper_spaces and
 81                  * swapper_spaces will be reused only after at least
 82                  * one grace period.  So it is impossible for them
 83                  * belongs to different usage.
 84                  */
 85                 nr = nr_swapper_spaces[i];
 86                 spaces = rcu_dereference(swapper_spaces[i]);
 87                 if (!nr || !spaces)
 88                         continue;
 89                 for (j = 0; j < nr; j++)
 90                         ret += spaces[j].nrpages;
 91         }
 92         rcu_read_unlock();
 93         return ret;
 94 }
 95 
 96 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
 97 
 98 void show_swap_cache_info(void)
 99 {
100         printk("%lu pages in swap cache\n", total_swapcache_pages());
101         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
102                 swap_cache_info.add_total, swap_cache_info.del_total,
103                 swap_cache_info.find_success, swap_cache_info.find_total);
104         printk("Free swap  = %ldkB\n",
105                 get_nr_swap_pages() << (PAGE_SHIFT - 10));
106         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
107 }
108 
109 /*
110  * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
111  * but sets SwapCache flag and private instead of mapping and index.
112  */
113 int __add_to_swap_cache(struct page *page, swp_entry_t entry)
114 {
115         int error, i, nr = hpage_nr_pages(page);
116         struct address_space *address_space;
117         pgoff_t idx = swp_offset(entry);
118 
119         VM_BUG_ON_PAGE(!PageLocked(page), page);
120         VM_BUG_ON_PAGE(PageSwapCache(page), page);
121         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
122 
123         page_ref_add(page, nr);
124         SetPageSwapCache(page);
125 
126         address_space = swap_address_space(entry);
127         spin_lock_irq(&address_space->tree_lock);
128         for (i = 0; i < nr; i++) {
129                 set_page_private(page + i, entry.val + i);
130                 error = radix_tree_insert(&address_space->page_tree,
131                                           idx + i, page + i);
132                 if (unlikely(error))
133                         break;
134         }
135         if (likely(!error)) {
136                 address_space->nrpages += nr;
137                 __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
138                 ADD_CACHE_INFO(add_total, nr);
139         } else {
140                 /*
141                  * Only the context which have set SWAP_HAS_CACHE flag
142                  * would call add_to_swap_cache().
143                  * So add_to_swap_cache() doesn't returns -EEXIST.
144                  */
145                 VM_BUG_ON(error == -EEXIST);
146                 set_page_private(page + i, 0UL);
147                 while (i--) {
148                         radix_tree_delete(&address_space->page_tree, idx + i);
149                         set_page_private(page + i, 0UL);
150                 }
151                 ClearPageSwapCache(page);
152                 page_ref_sub(page, nr);
153         }
154         spin_unlock_irq(&address_space->tree_lock);
155 
156         return error;
157 }
158 
159 
160 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
161 {
162         int error;
163 
164         error = radix_tree_maybe_preload_order(gfp_mask, compound_order(page));
165         if (!error) {
166                 error = __add_to_swap_cache(page, entry);
167                 radix_tree_preload_end();
168         }
169         return error;
170 }
171 
172 /*
173  * This must be called only on pages that have
174  * been verified to be in the swap cache.
175  */
176 void __delete_from_swap_cache(struct page *page)
177 {
178         struct address_space *address_space;
179         int i, nr = hpage_nr_pages(page);
180         swp_entry_t entry;
181         pgoff_t idx;
182 
183         VM_BUG_ON_PAGE(!PageLocked(page), page);
184         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
185         VM_BUG_ON_PAGE(PageWriteback(page), page);
186 
187         entry.val = page_private(page);
188         address_space = swap_address_space(entry);
189         idx = swp_offset(entry);
190         for (i = 0; i < nr; i++) {
191                 radix_tree_delete(&address_space->page_tree, idx + i);
192                 set_page_private(page + i, 0);
193         }
194         ClearPageSwapCache(page);
195         address_space->nrpages -= nr;
196         __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
197         ADD_CACHE_INFO(del_total, nr);
198 }
199 
200 /**
201  * add_to_swap - allocate swap space for a page
202  * @page: page we want to move to swap
203  *
204  * Allocate swap space for the page and add the page to the
205  * swap cache.  Caller needs to hold the page lock. 
206  */
207 int add_to_swap(struct page *page)
208 {
209         swp_entry_t entry;
210         int err;
211 
212         VM_BUG_ON_PAGE(!PageLocked(page), page);
213         VM_BUG_ON_PAGE(!PageUptodate(page), page);
214 
215         entry = get_swap_page(page);
216         if (!entry.val)
217                 return 0;
218 
219         if (mem_cgroup_try_charge_swap(page, entry))
220                 goto fail;
221 
222         /*
223          * Radix-tree node allocations from PF_MEMALLOC contexts could
224          * completely exhaust the page allocator. __GFP_NOMEMALLOC
225          * stops emergency reserves from being allocated.
226          *
227          * TODO: this could cause a theoretical memory reclaim
228          * deadlock in the swap out path.
229          */
230         /*
231          * Add it to the swap cache.
232          */
233         err = add_to_swap_cache(page, entry,
234                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
235         /* -ENOMEM radix-tree allocation failure */
236         if (err)
237                 /*
238                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
239                  * clear SWAP_HAS_CACHE flag.
240                  */
241                 goto fail;
242         /*
243          * Normally the page will be dirtied in unmap because its pte should be
244          * dirty. A special case is MADV_FREE page. The page'e pte could have
245          * dirty bit cleared but the page's SwapBacked bit is still set because
246          * clearing the dirty bit and SwapBacked bit has no lock protected. For
247          * such page, unmap will not set dirty bit for it, so page reclaim will
248          * not write the page out. This can cause data corruption when the page
249          * is swap in later. Always setting the dirty bit for the page solves
250          * the problem.
251          */
252         set_page_dirty(page);
253 
254         return 1;
255 
256 fail:
257         put_swap_page(page, entry);
258         return 0;
259 }
260 
261 /*
262  * This must be called only on pages that have
263  * been verified to be in the swap cache and locked.
264  * It will never put the page into the free list,
265  * the caller has a reference on the page.
266  */
267 void delete_from_swap_cache(struct page *page)
268 {
269         swp_entry_t entry;
270         struct address_space *address_space;
271 
272         entry.val = page_private(page);
273 
274         address_space = swap_address_space(entry);
275         spin_lock_irq(&address_space->tree_lock);
276         __delete_from_swap_cache(page);
277         spin_unlock_irq(&address_space->tree_lock);
278 
279         put_swap_page(page, entry);
280         page_ref_sub(page, hpage_nr_pages(page));
281 }
282 
283 /* 
284  * If we are the only user, then try to free up the swap cache. 
285  * 
286  * Its ok to check for PageSwapCache without the page lock
287  * here because we are going to recheck again inside
288  * try_to_free_swap() _with_ the lock.
289  *                                      - Marcelo
290  */
291 static inline void free_swap_cache(struct page *page)
292 {
293         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
294                 try_to_free_swap(page);
295                 unlock_page(page);
296         }
297 }
298 
299 /* 
300  * Perform a free_page(), also freeing any swap cache associated with
301  * this page if it is the last user of the page.
302  */
303 void free_page_and_swap_cache(struct page *page)
304 {
305         free_swap_cache(page);
306         if (!is_huge_zero_page(page))
307                 put_page(page);
308 }
309 
310 /*
311  * Passed an array of pages, drop them all from swapcache and then release
312  * them.  They are removed from the LRU and freed if this is their last use.
313  */
314 void free_pages_and_swap_cache(struct page **pages, int nr)
315 {
316         struct page **pagep = pages;
317         int i;
318 
319         lru_add_drain();
320         for (i = 0; i < nr; i++)
321                 free_swap_cache(pagep[i]);
322         release_pages(pagep, nr);
323 }
324 
325 /*
326  * Lookup a swap entry in the swap cache. A found page will be returned
327  * unlocked and with its refcount incremented - we rely on the kernel
328  * lock getting page table operations atomic even if we drop the page
329  * lock before returning.
330  */
331 struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
332                                unsigned long addr)
333 {
334         struct page *page;
335         unsigned long ra_info;
336         int win, hits, readahead;
337 
338         page = find_get_page(swap_address_space(entry), swp_offset(entry));
339 
340         INC_CACHE_INFO(find_total);
341         if (page) {
342                 INC_CACHE_INFO(find_success);
343                 if (unlikely(PageTransCompound(page)))
344                         return page;
345                 readahead = TestClearPageReadahead(page);
346                 if (vma) {
347                         ra_info = GET_SWAP_RA_VAL(vma);
348                         win = SWAP_RA_WIN(ra_info);
349                         hits = SWAP_RA_HITS(ra_info);
350                         if (readahead)
351                                 hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
352                         atomic_long_set(&vma->swap_readahead_info,
353                                         SWAP_RA_VAL(addr, win, hits));
354                 }
355                 if (readahead) {
356                         count_vm_event(SWAP_RA_HIT);
357                         if (!vma)
358                                 atomic_inc(&swapin_readahead_hits);
359                 }
360         }
361         return page;
362 }
363 
364 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
365                         struct vm_area_struct *vma, unsigned long addr,
366                         bool *new_page_allocated)
367 {
368         struct page *found_page, *new_page = NULL;
369         struct address_space *swapper_space = swap_address_space(entry);
370         int err;
371         *new_page_allocated = false;
372 
373         do {
374                 /*
375                  * First check the swap cache.  Since this is normally
376                  * called after lookup_swap_cache() failed, re-calling
377                  * that would confuse statistics.
378                  */
379                 found_page = find_get_page(swapper_space, swp_offset(entry));
380                 if (found_page)
381                         break;
382 
383                 /*
384                  * Just skip read ahead for unused swap slot.
385                  * During swap_off when swap_slot_cache is disabled,
386                  * we have to handle the race between putting
387                  * swap entry in swap cache and marking swap slot
388                  * as SWAP_HAS_CACHE.  That's done in later part of code or
389                  * else swap_off will be aborted if we return NULL.
390                  */
391                 if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
392                         break;
393 
394                 /*
395                  * Get a new page to read into from swap.
396                  */
397                 if (!new_page) {
398                         new_page = alloc_page_vma(gfp_mask, vma, addr);
399                         if (!new_page)
400                                 break;          /* Out of memory */
401                 }
402 
403                 /*
404                  * call radix_tree_preload() while we can wait.
405                  */
406                 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
407                 if (err)
408                         break;
409 
410                 /*
411                  * Swap entry may have been freed since our caller observed it.
412                  */
413                 err = swapcache_prepare(entry);
414                 if (err == -EEXIST) {
415                         radix_tree_preload_end();
416                         /*
417                          * We might race against get_swap_page() and stumble
418                          * across a SWAP_HAS_CACHE swap_map entry whose page
419                          * has not been brought into the swapcache yet.
420                          */
421                         cond_resched();
422                         continue;
423                 }
424                 if (err) {              /* swp entry is obsolete ? */
425                         radix_tree_preload_end();
426                         break;
427                 }
428 
429                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
430                 __SetPageLocked(new_page);
431                 __SetPageSwapBacked(new_page);
432                 err = __add_to_swap_cache(new_page, entry);
433                 if (likely(!err)) {
434                         radix_tree_preload_end();
435                         /*
436                          * Initiate read into locked page and return.
437                          */
438                         lru_cache_add_anon(new_page);
439                         *new_page_allocated = true;
440                         return new_page;
441                 }
442                 radix_tree_preload_end();
443                 __ClearPageLocked(new_page);
444                 /*
445                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
446                  * clear SWAP_HAS_CACHE flag.
447                  */
448                 put_swap_page(new_page, entry);
449         } while (err != -ENOMEM);
450 
451         if (new_page)
452                 put_page(new_page);
453         return found_page;
454 }
455 
456 /*
457  * Locate a page of swap in physical memory, reserving swap cache space
458  * and reading the disk if it is not already cached.
459  * A failure return means that either the page allocation failed or that
460  * the swap entry is no longer in use.
461  */
462 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
463                 struct vm_area_struct *vma, unsigned long addr, bool do_poll)
464 {
465         bool page_was_allocated;
466         struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
467                         vma, addr, &page_was_allocated);
468 
469         if (page_was_allocated)
470                 swap_readpage(retpage, do_poll);
471 
472         return retpage;
473 }
474 
475 static unsigned int __swapin_nr_pages(unsigned long prev_offset,
476                                       unsigned long offset,
477                                       int hits,
478                                       int max_pages,
479                                       int prev_win)
480 {
481         unsigned int pages, last_ra;
482 
483         /*
484          * This heuristic has been found to work well on both sequential and
485          * random loads, swapping to hard disk or to SSD: please don't ask
486          * what the "+ 2" means, it just happens to work well, that's all.
487          */
488         pages = hits + 2;
489         if (pages == 2) {
490                 /*
491                  * We can have no readahead hits to judge by: but must not get
492                  * stuck here forever, so check for an adjacent offset instead
493                  * (and don't even bother to check whether swap type is same).
494                  */
495                 if (offset != prev_offset + 1 && offset != prev_offset - 1)
496                         pages = 1;
497         } else {
498                 unsigned int roundup = 4;
499                 while (roundup < pages)
500                         roundup <<= 1;
501                 pages = roundup;
502         }
503 
504         if (pages > max_pages)
505                 pages = max_pages;
506 
507         /* Don't shrink readahead too fast */
508         last_ra = prev_win / 2;
509         if (pages < last_ra)
510                 pages = last_ra;
511 
512         return pages;
513 }
514 
515 static unsigned long swapin_nr_pages(unsigned long offset)
516 {
517         static unsigned long prev_offset;
518         unsigned int hits, pages, max_pages;
519         static atomic_t last_readahead_pages;
520 
521         max_pages = 1 << READ_ONCE(page_cluster);
522         if (max_pages <= 1)
523                 return 1;
524 
525         hits = atomic_xchg(&swapin_readahead_hits, 0);
526         pages = __swapin_nr_pages(prev_offset, offset, hits, max_pages,
527                                   atomic_read(&last_readahead_pages));
528         if (!hits)
529                 prev_offset = offset;
530         atomic_set(&last_readahead_pages, pages);
531 
532         return pages;
533 }
534 
535 /**
536  * swapin_readahead - swap in pages in hope we need them soon
537  * @entry: swap entry of this memory
538  * @gfp_mask: memory allocation flags
539  * @vma: user vma this address belongs to
540  * @addr: target address for mempolicy
541  *
542  * Returns the struct page for entry and addr, after queueing swapin.
543  *
544  * Primitive swap readahead code. We simply read an aligned block of
545  * (1 << page_cluster) entries in the swap area. This method is chosen
546  * because it doesn't cost us any seek time.  We also make sure to queue
547  * the 'original' request together with the readahead ones...
548  *
549  * This has been extended to use the NUMA policies from the mm triggering
550  * the readahead.
551  *
552  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
553  */
554 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
555                         struct vm_area_struct *vma, unsigned long addr)
556 {
557         struct page *page;
558         unsigned long entry_offset = swp_offset(entry);
559         unsigned long offset = entry_offset;
560         unsigned long start_offset, end_offset;
561         unsigned long mask;
562         struct swap_info_struct *si = swp_swap_info(entry);
563         struct blk_plug plug;
564         bool do_poll = true, page_allocated;
565 
566         mask = swapin_nr_pages(offset) - 1;
567         if (!mask)
568                 goto skip;
569 
570         do_poll = false;
571         /* Read a page_cluster sized and aligned cluster around offset. */
572         start_offset = offset & ~mask;
573         end_offset = offset | mask;
574         if (!start_offset)      /* First page is swap header. */
575                 start_offset++;
576         if (end_offset >= si->max)
577                 end_offset = si->max - 1;
578 
579         blk_start_plug(&plug);
580         for (offset = start_offset; offset <= end_offset ; offset++) {
581                 /* Ok, do the async read-ahead now */
582                 page = __read_swap_cache_async(
583                         swp_entry(swp_type(entry), offset),
584                         gfp_mask, vma, addr, &page_allocated);
585                 if (!page)
586                         continue;
587                 if (page_allocated) {
588                         swap_readpage(page, false);
589                         if (offset != entry_offset &&
590                             likely(!PageTransCompound(page))) {
591                                 SetPageReadahead(page);
592                                 count_vm_event(SWAP_RA);
593                         }
594                 }
595                 put_page(page);
596         }
597         blk_finish_plug(&plug);
598 
599         lru_add_drain();        /* Push any new pages onto the LRU now */
600 skip:
601         return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll);
602 }
603 
604 int init_swap_address_space(unsigned int type, unsigned long nr_pages)
605 {
606         struct address_space *spaces, *space;
607         unsigned int i, nr;
608 
609         nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
610         spaces = kvzalloc(sizeof(struct address_space) * nr, GFP_KERNEL);
611         if (!spaces)
612                 return -ENOMEM;
613         for (i = 0; i < nr; i++) {
614                 space = spaces + i;
615                 INIT_RADIX_TREE(&space->page_tree, GFP_ATOMIC|__GFP_NOWARN);
616                 atomic_set(&space->i_mmap_writable, 0);
617                 space->a_ops = &swap_aops;
618                 /* swap cache doesn't use writeback related tags */
619                 mapping_set_no_writeback_tags(space);
620                 spin_lock_init(&space->tree_lock);
621         }
622         nr_swapper_spaces[type] = nr;
623         rcu_assign_pointer(swapper_spaces[type], spaces);
624 
625         return 0;
626 }
627 
628 void exit_swap_address_space(unsigned int type)
629 {
630         struct address_space *spaces;
631 
632         spaces = swapper_spaces[type];
633         nr_swapper_spaces[type] = 0;
634         rcu_assign_pointer(swapper_spaces[type], NULL);
635         synchronize_rcu();
636         kvfree(spaces);
637 }
638 
639 static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,
640                                      unsigned long faddr,
641                                      unsigned long lpfn,
642                                      unsigned long rpfn,
643                                      unsigned long *start,
644                                      unsigned long *end)
645 {
646         *start = max3(lpfn, PFN_DOWN(vma->vm_start),
647                       PFN_DOWN(faddr & PMD_MASK));
648         *end = min3(rpfn, PFN_DOWN(vma->vm_end),
649                     PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
650 }
651 
652 struct page *swap_readahead_detect(struct vm_fault *vmf,
653                                    struct vma_swap_readahead *swap_ra)
654 {
655         struct vm_area_struct *vma = vmf->vma;
656         unsigned long swap_ra_info;
657         struct page *page;
658         swp_entry_t entry;
659         unsigned long faddr, pfn, fpfn;
660         unsigned long start, end;
661         pte_t *pte;
662         unsigned int max_win, hits, prev_win, win, left;
663 #ifndef CONFIG_64BIT
664         pte_t *tpte;
665 #endif
666 
667         max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
668                              SWAP_RA_ORDER_CEILING);
669         if (max_win == 1) {
670                 swap_ra->win = 1;
671                 return NULL;
672         }
673 
674         faddr = vmf->address;
675         entry = pte_to_swp_entry(vmf->orig_pte);
676         if ((unlikely(non_swap_entry(entry))))
677                 return NULL;
678         page = lookup_swap_cache(entry, vma, faddr);
679         if (page)
680                 return page;
681 
682         fpfn = PFN_DOWN(faddr);
683         swap_ra_info = GET_SWAP_RA_VAL(vma);
684         pfn = PFN_DOWN(SWAP_RA_ADDR(swap_ra_info));
685         prev_win = SWAP_RA_WIN(swap_ra_info);
686         hits = SWAP_RA_HITS(swap_ra_info);
687         swap_ra->win = win = __swapin_nr_pages(pfn, fpfn, hits,
688                                                max_win, prev_win);
689         atomic_long_set(&vma->swap_readahead_info,
690                         SWAP_RA_VAL(faddr, win, 0));
691 
692         if (win == 1)
693                 return NULL;
694 
695         /* Copy the PTEs because the page table may be unmapped */
696         if (fpfn == pfn + 1)
697                 swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
698         else if (pfn == fpfn + 1)
699                 swap_ra_clamp_pfn(vma, faddr, fpfn - win + 1, fpfn + 1,
700                                   &start, &end);
701         else {
702                 left = (win - 1) / 2;
703                 swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
704                                   &start, &end);
705         }
706         swap_ra->nr_pte = end - start;
707         swap_ra->offset = fpfn - start;
708         pte = vmf->pte - swap_ra->offset;
709 #ifdef CONFIG_64BIT
710         swap_ra->ptes = pte;
711 #else
712         tpte = swap_ra->ptes;
713         for (pfn = start; pfn != end; pfn++)
714                 *tpte++ = *pte++;
715 #endif
716 
717         return NULL;
718 }
719 
720 struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
721                                     struct vm_fault *vmf,
722                                     struct vma_swap_readahead *swap_ra)
723 {
724         struct blk_plug plug;
725         struct vm_area_struct *vma = vmf->vma;
726         struct page *page;
727         pte_t *pte, pentry;
728         swp_entry_t entry;
729         unsigned int i;
730         bool page_allocated;
731 
732         if (swap_ra->win == 1)
733                 goto skip;
734 
735         blk_start_plug(&plug);
736         for (i = 0, pte = swap_ra->ptes; i < swap_ra->nr_pte;
737              i++, pte++) {
738                 pentry = *pte;
739                 if (pte_none(pentry))
740                         continue;
741                 if (pte_present(pentry))
742                         continue;
743                 entry = pte_to_swp_entry(pentry);
744                 if (unlikely(non_swap_entry(entry)))
745                         continue;
746                 page = __read_swap_cache_async(entry, gfp_mask, vma,
747                                                vmf->address, &page_allocated);
748                 if (!page)
749                         continue;
750                 if (page_allocated) {
751                         swap_readpage(page, false);
752                         if (i != swap_ra->offset &&
753                             likely(!PageTransCompound(page))) {
754                                 SetPageReadahead(page);
755                                 count_vm_event(SWAP_RA);
756                         }
757                 }
758                 put_page(page);
759         }
760         blk_finish_plug(&plug);
761         lru_add_drain();
762 skip:
763         return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
764                                      swap_ra->win == 1);
765 }
766 
767 #ifdef CONFIG_SYSFS
768 static ssize_t vma_ra_enabled_show(struct kobject *kobj,
769                                      struct kobj_attribute *attr, char *buf)
770 {
771         return sprintf(buf, "%s\n", swap_vma_readahead ? "true" : "false");
772 }
773 static ssize_t vma_ra_enabled_store(struct kobject *kobj,
774                                       struct kobj_attribute *attr,
775                                       const char *buf, size_t count)
776 {
777         if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1))
778                 swap_vma_readahead = true;
779         else if (!strncmp(buf, "false", 5) || !strncmp(buf, "", 1))
780                 swap_vma_readahead = false;
781         else
782                 return -EINVAL;
783 
784         return count;
785 }
786 static struct kobj_attribute vma_ra_enabled_attr =
787         __ATTR(vma_ra_enabled, 0644, vma_ra_enabled_show,
788                vma_ra_enabled_store);
789 
790 static struct attribute *swap_attrs[] = {
791         &vma_ra_enabled_attr.attr,
792         NULL,
793 };
794 
795 static struct attribute_group swap_attr_group = {
796         .attrs = swap_attrs,
797 };
798 
799 static int __init swap_init_sysfs(void)
800 {
801         int err;
802         struct kobject *swap_kobj;
803 
804         swap_kobj = kobject_create_and_add("swap", mm_kobj);
805         if (!swap_kobj) {
806                 pr_err("failed to create swap kobject\n");
807                 return -ENOMEM;
808         }
809         err = sysfs_create_group(swap_kobj, &swap_attr_group);
810         if (err) {
811                 pr_err("failed to register swap group\n");
812                 goto delete_obj;
813         }
814         return 0;
815 
816 delete_obj:
817         kobject_put(swap_kobj);
818         return err;
819 }
820 subsys_initcall(swap_init_sysfs);
821 #endif
822 

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