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>
25 #include <asm/pgtable.h>
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 };
39 struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
40 static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
41 static bool enable_vma_readahead __read_mostly = true;
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)
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)
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))
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)
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)
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;
71 unsigned long total_swapcache_pages(void)
72 {
73 unsigned int i, j, nr;
74 unsigned long ret = 0;
75 struct address_space *spaces;
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 }
96 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
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 }
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);
119 VM_BUG_ON_PAGE(!PageLocked(page), page);
120 VM_BUG_ON_PAGE(PageSwapCache(page), page);
121 VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
123 page_ref_add(page, nr);
124 SetPageSwapCache(page);
126 address_space = swap_address_space(entry);
127 xa_lock_irq(&address_space->i_pages);
128 for (i = 0; i < nr; i++) {
129 set_page_private(page + i, entry.val + i);
130 error = radix_tree_insert(&address_space->i_pages,
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->i_pages, idx + i);
149 set_page_private(page + i, 0UL);
150 }
151 ClearPageSwapCache(page);
152 page_ref_sub(page, nr);
153 }
154 xa_unlock_irq(&address_space->i_pages);
156 return error;
157 }
160 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
161 {
162 int error;
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 }
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;
183 VM_BUG_ON_PAGE(!PageLocked(page), page);
184 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
185 VM_BUG_ON_PAGE(PageWriteback(page), page);
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->i_pages, 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 }
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;
212 VM_BUG_ON_PAGE(!PageLocked(page), page);
213 VM_BUG_ON_PAGE(!PageUptodate(page), page);
215 entry = get_swap_page(page);
216 if (!entry.val)
217 return 0;
219 /*
220 * Radix-tree node allocations from PF_MEMALLOC contexts could
221 * completely exhaust the page allocator. __GFP_NOMEMALLOC
222 * stops emergency reserves from being allocated.
223 *
224 * TODO: this could cause a theoretical memory reclaim
225 * deadlock in the swap out path.
226 */
227 /*
228 * Add it to the swap cache.
229 */
230 err = add_to_swap_cache(page, entry,
231 __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
232 /* -ENOMEM radix-tree allocation failure */
233 if (err)
234 /*
235 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
236 * clear SWAP_HAS_CACHE flag.
237 */
238 goto fail;
239 /*
240 * Normally the page will be dirtied in unmap because its pte should be
241 * dirty. A special case is MADV_FREE page. The page'e pte could have
242 * dirty bit cleared but the page's SwapBacked bit is still set because
243 * clearing the dirty bit and SwapBacked bit has no lock protected. For
244 * such page, unmap will not set dirty bit for it, so page reclaim will
245 * not write the page out. This can cause data corruption when the page
246 * is swap in later. Always setting the dirty bit for the page solves
247 * the problem.
248 */
249 set_page_dirty(page);
251 return 1;
253 fail:
254 put_swap_page(page, entry);
255 return 0;
256 }
258 /*
259 * This must be called only on pages that have
260 * been verified to be in the swap cache and locked.
261 * It will never put the page into the free list,
262 * the caller has a reference on the page.
263 */
264 void delete_from_swap_cache(struct page *page)
265 {
266 swp_entry_t entry;
267 struct address_space *address_space;
269 entry.val = page_private(page);
271 address_space = swap_address_space(entry);
272 xa_lock_irq(&address_space->i_pages);
273 __delete_from_swap_cache(page);
274 xa_unlock_irq(&address_space->i_pages);
276 put_swap_page(page, entry);
277 page_ref_sub(page, hpage_nr_pages(page));
278 }
280 /*
281 * If we are the only user, then try to free up the swap cache.
282 *
283 * Its ok to check for PageSwapCache without the page lock
284 * here because we are going to recheck again inside
285 * try_to_free_swap() _with_ the lock.
286 * - Marcelo
287 */
288 static inline void free_swap_cache(struct page *page)
289 {
290 if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
291 try_to_free_swap(page);
292 unlock_page(page);
293 }
294 }
296 /*
297 * Perform a free_page(), also freeing any swap cache associated with
298 * this page if it is the last user of the page.
299 */
300 void free_page_and_swap_cache(struct page *page)
301 {
302 free_swap_cache(page);
303 if (!is_huge_zero_page(page))
304 put_page(page);
305 }
307 /*
308 * Passed an array of pages, drop them all from swapcache and then release
309 * them. They are removed from the LRU and freed if this is their last use.
310 */
311 void free_pages_and_swap_cache(struct page **pages, int nr)
312 {
313 struct page **pagep = pages;
314 int i;
316 lru_add_drain();
317 for (i = 0; i < nr; i++)
318 free_swap_cache(pagep[i]);
319 release_pages(pagep, nr);
320 }
322 static inline bool swap_use_vma_readahead(void)
323 {
324 return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
325 }
327 /*
328 * Lookup a swap entry in the swap cache. A found page will be returned
329 * unlocked and with its refcount incremented - we rely on the kernel
330 * lock getting page table operations atomic even if we drop the page
331 * lock before returning.
332 */
333 struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
334 unsigned long addr)
335 {
336 struct page *page;
338 page = find_get_page(swap_address_space(entry), swp_offset(entry));
340 INC_CACHE_INFO(find_total);
341 if (page) {
342 bool vma_ra = swap_use_vma_readahead();
343 bool readahead;
345 INC_CACHE_INFO(find_success);
346 /*
347 * At the moment, we don't support PG_readahead for anon THP
348 * so let's bail out rather than confusing the readahead stat.
349 */
350 if (unlikely(PageTransCompound(page)))
351 return page;
353 readahead = TestClearPageReadahead(page);
354 if (vma && vma_ra) {
355 unsigned long ra_val;
356 int win, hits;
358 ra_val = GET_SWAP_RA_VAL(vma);
359 win = SWAP_RA_WIN(ra_val);
360 hits = SWAP_RA_HITS(ra_val);
361 if (readahead)
362 hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
363 atomic_long_set(&vma->swap_readahead_info,
364 SWAP_RA_VAL(addr, win, hits));
365 }
367 if (readahead) {
368 count_vm_event(SWAP_RA_HIT);
369 if (!vma || !vma_ra)
370 atomic_inc(&swapin_readahead_hits);
371 }
372 }
374 return page;
375 }
377 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
378 struct vm_area_struct *vma, unsigned long addr,
379 bool *new_page_allocated)
380 {
381 struct page *found_page, *new_page = NULL;
382 struct address_space *swapper_space = swap_address_space(entry);
383 int err;
384 *new_page_allocated = false;
386 do {
387 /*
388 * First check the swap cache. Since this is normally
389 * called after lookup_swap_cache() failed, re-calling
390 * that would confuse statistics.
391 */
392 found_page = find_get_page(swapper_space, swp_offset(entry));
393 if (found_page)
394 break;
396 /*
397 * Just skip read ahead for unused swap slot.
398 * During swap_off when swap_slot_cache is disabled,
399 * we have to handle the race between putting
400 * swap entry in swap cache and marking swap slot
401 * as SWAP_HAS_CACHE. That's done in later part of code or
402 * else swap_off will be aborted if we return NULL.
403 */
404 if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
405 break;
407 /*
408 * Get a new page to read into from swap.
409 */
410 if (!new_page) {
411 new_page = alloc_page_vma(gfp_mask, vma, addr);
412 if (!new_page)
413 break; /* Out of memory */
414 }
416 /*
417 * call radix_tree_preload() while we can wait.
418 */
419 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
420 if (err)
421 break;
423 /*
424 * Swap entry may have been freed since our caller observed it.
425 */
426 err = swapcache_prepare(entry);
427 if (err == -EEXIST) {
428 radix_tree_preload_end();
429 /*
430 * We might race against get_swap_page() and stumble
431 * across a SWAP_HAS_CACHE swap_map entry whose page
432 * has not been brought into the swapcache yet.
433 */
434 cond_resched();
435 continue;
436 }
437 if (err) { /* swp entry is obsolete ? */
438 radix_tree_preload_end();
439 break;
440 }
442 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
443 __SetPageLocked(new_page);
444 __SetPageSwapBacked(new_page);
445 err = __add_to_swap_cache(new_page, entry);
446 if (likely(!err)) {
447 radix_tree_preload_end();
448 /*
449 * Initiate read into locked page and return.
450 */
451 lru_cache_add_anon(new_page);
452 *new_page_allocated = true;
453 return new_page;
454 }
455 radix_tree_preload_end();
456 __ClearPageLocked(new_page);
457 /*
458 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
459 * clear SWAP_HAS_CACHE flag.
460 */
461 put_swap_page(new_page, entry);
462 } while (err != -ENOMEM);
464 if (new_page)
465 put_page(new_page);
466 return found_page;
467 }
469 /*
470 * Locate a page of swap in physical memory, reserving swap cache space
471 * and reading the disk if it is not already cached.
472 * A failure return means that either the page allocation failed or that
473 * the swap entry is no longer in use.
474 */
475 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
476 struct vm_area_struct *vma, unsigned long addr, bool do_poll)
477 {
478 bool page_was_allocated;
479 struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
480 vma, addr, &page_was_allocated);
482 if (page_was_allocated)
483 swap_readpage(retpage, do_poll);
485 return retpage;
486 }
488 static unsigned int __swapin_nr_pages(unsigned long prev_offset,
489 unsigned long offset,
490 int hits,
491 int max_pages,
492 int prev_win)
493 {
494 unsigned int pages, last_ra;
496 /*
497 * This heuristic has been found to work well on both sequential and
498 * random loads, swapping to hard disk or to SSD: please don't ask
499 * what the "+ 2" means, it just happens to work well, that's all.
500 */
501 pages = hits + 2;
502 if (pages == 2) {
503 /*
504 * We can have no readahead hits to judge by: but must not get
505 * stuck here forever, so check for an adjacent offset instead
506 * (and don't even bother to check whether swap type is same).
507 */
508 if (offset != prev_offset + 1 && offset != prev_offset - 1)
509 pages = 1;
510 } else {
511 unsigned int roundup = 4;
512 while (roundup < pages)
513 roundup <<= 1;
514 pages = roundup;
515 }
517 if (pages > max_pages)
518 pages = max_pages;
520 /* Don't shrink readahead too fast */
521 last_ra = prev_win / 2;
522 if (pages < last_ra)
523 pages = last_ra;
525 return pages;
526 }
528 static unsigned long swapin_nr_pages(unsigned long offset)
529 {
530 static unsigned long prev_offset;
531 unsigned int hits, pages, max_pages;
532 static atomic_t last_readahead_pages;
534 max_pages = 1 << READ_ONCE(page_cluster);
535 if (max_pages <= 1)
536 return 1;
538 hits = atomic_xchg(&swapin_readahead_hits, 0);
539 pages = __swapin_nr_pages(prev_offset, offset, hits, max_pages,
540 atomic_read(&last_readahead_pages));
541 if (!hits)
542 prev_offset = offset;
543 atomic_set(&last_readahead_pages, pages);
545 return pages;
546 }
548 /**
549 * swap_cluster_readahead - swap in pages in hope we need them soon
550 * @entry: swap entry of this memory
551 * @gfp_mask: memory allocation flags
552 * @vmf: fault information
553 *
554 * Returns the struct page for entry and addr, after queueing swapin.
555 *
556 * Primitive swap readahead code. We simply read an aligned block of
557 * (1 << page_cluster) entries in the swap area. This method is chosen
558 * because it doesn't cost us any seek time. We also make sure to queue
559 * the 'original' request together with the readahead ones...
560 *
561 * This has been extended to use the NUMA policies from the mm triggering
562 * the readahead.
563 *
564 * Caller must hold down_read on the vma->vm_mm if vmf->vma is not NULL.
565 */
566 struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
567 struct vm_fault *vmf)
568 {
569 struct page *page;
570 unsigned long entry_offset = swp_offset(entry);
571 unsigned long offset = entry_offset;
572 unsigned long start_offset, end_offset;
573 unsigned long mask;
574 struct swap_info_struct *si = swp_swap_info(entry);
575 struct blk_plug plug;
576 bool do_poll = true, page_allocated;
577 struct vm_area_struct *vma = vmf->vma;
578 unsigned long addr = vmf->address;
580 mask = swapin_nr_pages(offset) - 1;
581 if (!mask)
582 goto skip;
584 do_poll = false;
585 /* Read a page_cluster sized and aligned cluster around offset. */
586 start_offset = offset & ~mask;
587 end_offset = offset | mask;
588 if (!start_offset) /* First page is swap header. */
589 start_offset++;
590 if (end_offset >= si->max)
591 end_offset = si->max - 1;
593 blk_start_plug(&plug);
594 for (offset = start_offset; offset <= end_offset ; offset++) {
595 /* Ok, do the async read-ahead now */
596 page = __read_swap_cache_async(
597 swp_entry(swp_type(entry), offset),
598 gfp_mask, vma, addr, &page_allocated);
599 if (!page)
600 continue;
601 if (page_allocated) {
602 swap_readpage(page, false);
603 if (offset != entry_offset) {
604 SetPageReadahead(page);
605 count_vm_event(SWAP_RA);
606 }
607 }
608 put_page(page);
609 }
610 blk_finish_plug(&plug);
612 lru_add_drain(); /* Push any new pages onto the LRU now */
613 skip:
614 return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll);
615 }
617 int init_swap_address_space(unsigned int type, unsigned long nr_pages)
618 {
619 struct address_space *spaces, *space;
620 unsigned int i, nr;
622 nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
623 spaces = kvcalloc(nr, sizeof(struct address_space), GFP_KERNEL);
624 if (!spaces)
625 return -ENOMEM;
626 for (i = 0; i < nr; i++) {
627 space = spaces + i;
628 INIT_RADIX_TREE(&space->i_pages, GFP_ATOMIC|__GFP_NOWARN);
629 atomic_set(&space->i_mmap_writable, 0);
630 space->a_ops = &swap_aops;
631 /* swap cache doesn't use writeback related tags */
632 mapping_set_no_writeback_tags(space);
633 }
634 nr_swapper_spaces[type] = nr;
635 rcu_assign_pointer(swapper_spaces[type], spaces);
637 return 0;
638 }
640 void exit_swap_address_space(unsigned int type)
641 {
642 struct address_space *spaces;
644 spaces = swapper_spaces[type];
645 nr_swapper_spaces[type] = 0;
646 rcu_assign_pointer(swapper_spaces[type], NULL);
647 synchronize_rcu();
648 kvfree(spaces);
649 }
651 static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,
652 unsigned long faddr,
653 unsigned long lpfn,
654 unsigned long rpfn,
655 unsigned long *start,
656 unsigned long *end)
657 {
658 *start = max3(lpfn, PFN_DOWN(vma->vm_start),
659 PFN_DOWN(faddr & PMD_MASK));
660 *end = min3(rpfn, PFN_DOWN(vma->vm_end),
661 PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
662 }
664 static void swap_ra_info(struct vm_fault *vmf,
665 struct vma_swap_readahead *ra_info)
666 {
667 struct vm_area_struct *vma = vmf->vma;
668 unsigned long ra_val;
669 swp_entry_t entry;
670 unsigned long faddr, pfn, fpfn;
671 unsigned long start, end;
672 pte_t *pte, *orig_pte;
673 unsigned int max_win, hits, prev_win, win, left;
674 #ifndef CONFIG_64BIT
675 pte_t *tpte;
676 #endif
678 max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
679 SWAP_RA_ORDER_CEILING);
680 if (max_win == 1) {
681 ra_info->win = 1;
682 return;
683 }
685 faddr = vmf->address;
686 orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
687 entry = pte_to_swp_entry(*pte);
688 if ((unlikely(non_swap_entry(entry)))) {
689 pte_unmap(orig_pte);
690 return;
691 }
693 fpfn = PFN_DOWN(faddr);
694 ra_val = GET_SWAP_RA_VAL(vma);
695 pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
696 prev_win = SWAP_RA_WIN(ra_val);
697 hits = SWAP_RA_HITS(ra_val);
698 ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits,
699 max_win, prev_win);
700 atomic_long_set(&vma->swap_readahead_info,
701 SWAP_RA_VAL(faddr, win, 0));
703 if (win == 1) {
704 pte_unmap(orig_pte);
705 return;
706 }
708 /* Copy the PTEs because the page table may be unmapped */
709 if (fpfn == pfn + 1)
710 swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
711 else if (pfn == fpfn + 1)
712 swap_ra_clamp_pfn(vma, faddr, fpfn - win + 1, fpfn + 1,
713 &start, &end);
714 else {
715 left = (win - 1) / 2;
716 swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
717 &start, &end);
718 }
719 ra_info->nr_pte = end - start;
720 ra_info->offset = fpfn - start;
721 pte -= ra_info->offset;
722 #ifdef CONFIG_64BIT
723 ra_info->ptes = pte;
724 #else
725 tpte = ra_info->ptes;
726 for (pfn = start; pfn != end; pfn++)
727 *tpte++ = *pte++;
728 #endif
729 pte_unmap(orig_pte);
730 }
732 static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask,
733 struct vm_fault *vmf)
734 {
735 struct blk_plug plug;
736 struct vm_area_struct *vma = vmf->vma;
737 struct page *page;
738 pte_t *pte, pentry;
739 swp_entry_t entry;
740 unsigned int i;
741 bool page_allocated;
742 struct vma_swap_readahead ra_info = {0,};
744 swap_ra_info(vmf, &ra_info);
745 if (ra_info.win == 1)
746 goto skip;
748 blk_start_plug(&plug);
749 for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
750 i++, pte++) {
751 pentry = *pte;
752 if (pte_none(pentry))
753 continue;
754 if (pte_present(pentry))
755 continue;
756 entry = pte_to_swp_entry(pentry);
757 if (unlikely(non_swap_entry(entry)))
758 continue;
759 page = __read_swap_cache_async(entry, gfp_mask, vma,
760 vmf->address, &page_allocated);
761 if (!page)
762 continue;
763 if (page_allocated) {
764 swap_readpage(page, false);
765 if (i != ra_info.offset) {
766 SetPageReadahead(page);
767 count_vm_event(SWAP_RA);
768 }
769 }
770 put_page(page);
771 }
772 blk_finish_plug(&plug);
773 lru_add_drain();
774 skip:
775 return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
776 ra_info.win == 1);
777 }
779 /**
780 * swapin_readahead - swap in pages in hope we need them soon
781 * @entry: swap entry of this memory
782 * @gfp_mask: memory allocation flags
783 * @vmf: fault information
784 *
785 * Returns the struct page for entry and addr, after queueing swapin.
786 *
787 * It's a main entry function for swap readahead. By the configuration,
788 * it will read ahead blocks by cluster-based(ie, physical disk based)
789 * or vma-based(ie, virtual address based on faulty address) readahead.
790 */
791 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
792 struct vm_fault *vmf)
793 {
794 return swap_use_vma_readahead() ?
795 swap_vma_readahead(entry, gfp_mask, vmf) :
796 swap_cluster_readahead(entry, gfp_mask, vmf);
797 }
799 #ifdef CONFIG_SYSFS
800 static ssize_t vma_ra_enabled_show(struct kobject *kobj,
801 struct kobj_attribute *attr, char *buf)
802 {
803 return sprintf(buf, "%s\n", enable_vma_readahead ? "true" : "false");
804 }
805 static ssize_t vma_ra_enabled_store(struct kobject *kobj,
806 struct kobj_attribute *attr,
807 const char *buf, size_t count)
808 {
809 if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1))
810 enable_vma_readahead = true;
811 else if (!strncmp(buf, "false", 5) || !strncmp(buf, "0", 1))
812 enable_vma_readahead = false;
813 else
814 return -EINVAL;
816 return count;
817 }
818 static struct kobj_attribute vma_ra_enabled_attr =
819 __ATTR(vma_ra_enabled, 0644, vma_ra_enabled_show,
820 vma_ra_enabled_store);
822 static struct attribute *swap_attrs[] = {
823 &vma_ra_enabled_attr.attr,
824 NULL,
825 };
827 static struct attribute_group swap_attr_group = {
828 .attrs = swap_attrs,
829 };
831 static int __init swap_init_sysfs(void)
832 {
833 int err;
834 struct kobject *swap_kobj;
836 swap_kobj = kobject_create_and_add("swap", mm_kobj);
837 if (!swap_kobj) {
838 pr_err("failed to create swap kobject\n");
839 return -ENOMEM;
840 }
841 err = sysfs_create_group(swap_kobj, &swap_attr_group);
842 if (err) {
843 pr_err("failed to register swap group\n");
844 goto delete_obj;
845 }
846 return 0;
848 delete_obj:
849 kobject_put(swap_kobj);
850 return err;
851 }
852 subsys_initcall(swap_init_sysfs);
853 #endif