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/mempolicy.h>
14#include <linux/swap.h>
15#include <linux/swapops.h>
16#include <linux/init.h>
17#include <linux/pagemap.h>
18#include <linux/backing-dev.h>
19#include <linux/blkdev.h>
20#include <linux/migrate.h>
21#include <linux/vmalloc.h>
22#include <linux/swap_slots.h>
23#include <linux/huge_mm.h>
24#include <linux/shmem_fs.h>
25#include "internal.h"
26#include "swap.h"
27
28/*
29 * swapper_space is a fiction, retained to simplify the path through
30 * vmscan's shrink_page_list.
31 */
32static const struct address_space_operations swap_aops = {
33 .writepage = swap_writepage,
34 .dirty_folio = noop_dirty_folio,
35#ifdef CONFIG_MIGRATION
36 .migrate_folio = migrate_folio,
37#endif
38};
39
40struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
41static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
42static bool enable_vma_readahead __read_mostly = true;
43
44#define SWAP_RA_WIN_SHIFT (PAGE_SHIFT / 2)
45#define SWAP_RA_HITS_MASK ((1UL << SWAP_RA_WIN_SHIFT) - 1)
46#define SWAP_RA_HITS_MAX SWAP_RA_HITS_MASK
47#define SWAP_RA_WIN_MASK (~PAGE_MASK & ~SWAP_RA_HITS_MASK)
48
49#define SWAP_RA_HITS(v) ((v) & SWAP_RA_HITS_MASK)
50#define SWAP_RA_WIN(v) (((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT)
51#define SWAP_RA_ADDR(v) ((v) & PAGE_MASK)
52
53#define SWAP_RA_VAL(addr, win, hits) \
54 (((addr) & PAGE_MASK) | \
55 (((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) | \
56 ((hits) & SWAP_RA_HITS_MASK))
57
58/* Initial readahead hits is 4 to start up with a small window */
59#define GET_SWAP_RA_VAL(vma) \
60 (atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
61
62static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
63
64void show_swap_cache_info(void)
65{
66 printk("%lu pages in swap cache\n", total_swapcache_pages());
67 printk("Free swap = %ldkB\n", K(get_nr_swap_pages()));
68 printk("Total swap = %lukB\n", K(total_swap_pages));
69}
70
71void *get_shadow_from_swap_cache(swp_entry_t entry)
72{
73 struct address_space *address_space = swap_address_space(entry);
74 pgoff_t idx = swp_offset(entry);
75 struct page *page;
76
77 page = xa_load(&address_space->i_pages, index: idx);
78 if (xa_is_value(entry: page))
79 return page;
80 return NULL;
81}
82
83/*
84 * add_to_swap_cache resembles filemap_add_folio on swapper_space,
85 * but sets SwapCache flag and private instead of mapping and index.
86 */
87int add_to_swap_cache(struct folio *folio, swp_entry_t entry,
88 gfp_t gfp, void **shadowp)
89{
90 struct address_space *address_space = swap_address_space(entry);
91 pgoff_t idx = swp_offset(entry);
92 XA_STATE_ORDER(xas, &address_space->i_pages, idx, folio_order(folio));
93 unsigned long i, nr = folio_nr_pages(folio);
94 void *old;
95
96 xas_set_update(xas: &xas, update: workingset_update_node);
97
98 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
99 VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio);
100 VM_BUG_ON_FOLIO(!folio_test_swapbacked(folio), folio);
101
102 folio_ref_add(folio, nr);
103 folio_set_swapcache(folio);
104 folio->swap = entry;
105
106 do {
107 xas_lock_irq(&xas);
108 xas_create_range(&xas);
109 if (xas_error(xas: &xas))
110 goto unlock;
111 for (i = 0; i < nr; i++) {
112 VM_BUG_ON_FOLIO(xas.xa_index != idx + i, folio);
113 if (shadowp) {
114 old = xas_load(&xas);
115 if (xa_is_value(entry: old))
116 *shadowp = old;
117 }
118 xas_store(&xas, entry: folio);
119 xas_next(xas: &xas);
120 }
121 address_space->nrpages += nr;
122 __node_stat_mod_folio(folio, item: NR_FILE_PAGES, nr);
123 __lruvec_stat_mod_folio(folio, idx: NR_SWAPCACHE, val: nr);
124unlock:
125 xas_unlock_irq(&xas);
126 } while (xas_nomem(&xas, gfp));
127
128 if (!xas_error(xas: &xas))
129 return 0;
130
131 folio_clear_swapcache(folio);
132 folio_ref_sub(folio, nr);
133 return xas_error(xas: &xas);
134}
135
136/*
137 * This must be called only on folios that have
138 * been verified to be in the swap cache.
139 */
140void __delete_from_swap_cache(struct folio *folio,
141 swp_entry_t entry, void *shadow)
142{
143 struct address_space *address_space = swap_address_space(entry);
144 int i;
145 long nr = folio_nr_pages(folio);
146 pgoff_t idx = swp_offset(entry);
147 XA_STATE(xas, &address_space->i_pages, idx);
148
149 xas_set_update(xas: &xas, update: workingset_update_node);
150
151 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
152 VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
153 VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio);
154
155 for (i = 0; i < nr; i++) {
156 void *entry = xas_store(&xas, entry: shadow);
157 VM_BUG_ON_PAGE(entry != folio, entry);
158 xas_next(xas: &xas);
159 }
160 folio->swap.val = 0;
161 folio_clear_swapcache(folio);
162 address_space->nrpages -= nr;
163 __node_stat_mod_folio(folio, item: NR_FILE_PAGES, nr: -nr);
164 __lruvec_stat_mod_folio(folio, idx: NR_SWAPCACHE, val: -nr);
165}
166
167/**
168 * add_to_swap - allocate swap space for a folio
169 * @folio: folio we want to move to swap
170 *
171 * Allocate swap space for the folio and add the folio to the
172 * swap cache.
173 *
174 * Context: Caller needs to hold the folio lock.
175 * Return: Whether the folio was added to the swap cache.
176 */
177bool add_to_swap(struct folio *folio)
178{
179 swp_entry_t entry;
180 int err;
181
182 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
183 VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);
184
185 entry = folio_alloc_swap(folio);
186 if (!entry.val)
187 return false;
188
189 /*
190 * XArray node allocations from PF_MEMALLOC contexts could
191 * completely exhaust the page allocator. __GFP_NOMEMALLOC
192 * stops emergency reserves from being allocated.
193 *
194 * TODO: this could cause a theoretical memory reclaim
195 * deadlock in the swap out path.
196 */
197 /*
198 * Add it to the swap cache.
199 */
200 err = add_to_swap_cache(folio, entry,
201 __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN, NULL);
202 if (err)
203 /*
204 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
205 * clear SWAP_HAS_CACHE flag.
206 */
207 goto fail;
208 /*
209 * Normally the folio will be dirtied in unmap because its
210 * pte should be dirty. A special case is MADV_FREE page. The
211 * page's pte could have dirty bit cleared but the folio's
212 * SwapBacked flag is still set because clearing the dirty bit
213 * and SwapBacked flag has no lock protected. For such folio,
214 * unmap will not set dirty bit for it, so folio reclaim will
215 * not write the folio out. This can cause data corruption when
216 * the folio is swapped in later. Always setting the dirty flag
217 * for the folio solves the problem.
218 */
219 folio_mark_dirty(folio);
220
221 return true;
222
223fail:
224 put_swap_folio(folio, entry);
225 return false;
226}
227
228/*
229 * This must be called only on folios that have
230 * been verified to be in the swap cache and locked.
231 * It will never put the folio into the free list,
232 * the caller has a reference on the folio.
233 */
234void delete_from_swap_cache(struct folio *folio)
235{
236 swp_entry_t entry = folio->swap;
237 struct address_space *address_space = swap_address_space(entry);
238
239 xa_lock_irq(&address_space->i_pages);
240 __delete_from_swap_cache(folio, entry, NULL);
241 xa_unlock_irq(&address_space->i_pages);
242
243 put_swap_folio(folio, entry);
244 folio_ref_sub(folio, nr: folio_nr_pages(folio));
245}
246
247void clear_shadow_from_swap_cache(int type, unsigned long begin,
248 unsigned long end)
249{
250 unsigned long curr = begin;
251 void *old;
252
253 for (;;) {
254 swp_entry_t entry = swp_entry(type, offset: curr);
255 struct address_space *address_space = swap_address_space(entry);
256 XA_STATE(xas, &address_space->i_pages, curr);
257
258 xas_set_update(xas: &xas, update: workingset_update_node);
259
260 xa_lock_irq(&address_space->i_pages);
261 xas_for_each(&xas, old, end) {
262 if (!xa_is_value(entry: old))
263 continue;
264 xas_store(&xas, NULL);
265 }
266 xa_unlock_irq(&address_space->i_pages);
267
268 /* search the next swapcache until we meet end */
269 curr >>= SWAP_ADDRESS_SPACE_SHIFT;
270 curr++;
271 curr <<= SWAP_ADDRESS_SPACE_SHIFT;
272 if (curr > end)
273 break;
274 }
275}
276
277/*
278 * If we are the only user, then try to free up the swap cache.
279 *
280 * Its ok to check the swapcache flag without the folio lock
281 * here because we are going to recheck again inside
282 * folio_free_swap() _with_ the lock.
283 * - Marcelo
284 */
285void free_swap_cache(struct page *page)
286{
287 struct folio *folio = page_folio(page);
288
289 if (folio_test_swapcache(folio) && !folio_mapped(folio) &&
290 folio_trylock(folio)) {
291 folio_free_swap(folio);
292 folio_unlock(folio);
293 }
294}
295
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 */
300void 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}
306
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 */
311void free_pages_and_swap_cache(struct encoded_page **pages, int nr)
312{
313 lru_add_drain();
314 for (int i = 0; i < nr; i++)
315 free_swap_cache(page: encoded_page_ptr(page: pages[i]));
316 release_pages(pages, nr);
317}
318
319static inline bool swap_use_vma_readahead(void)
320{
321 return READ_ONCE(enable_vma_readahead) && !atomic_read(v: &nr_rotate_swap);
322}
323
324/*
325 * Lookup a swap entry in the swap cache. A found folio will be returned
326 * unlocked and with its refcount incremented - we rely on the kernel
327 * lock getting page table operations atomic even if we drop the folio
328 * lock before returning.
329 *
330 * Caller must lock the swap device or hold a reference to keep it valid.
331 */
332struct folio *swap_cache_get_folio(swp_entry_t entry,
333 struct vm_area_struct *vma, unsigned long addr)
334{
335 struct folio *folio;
336
337 folio = filemap_get_folio(swap_address_space(entry), index: swp_offset(entry));
338 if (!IS_ERR(ptr: folio)) {
339 bool vma_ra = swap_use_vma_readahead();
340 bool readahead;
341
342 /*
343 * At the moment, we don't support PG_readahead for anon THP
344 * so let's bail out rather than confusing the readahead stat.
345 */
346 if (unlikely(folio_test_large(folio)))
347 return folio;
348
349 readahead = folio_test_clear_readahead(folio);
350 if (vma && vma_ra) {
351 unsigned long ra_val;
352 int win, hits;
353
354 ra_val = GET_SWAP_RA_VAL(vma);
355 win = SWAP_RA_WIN(ra_val);
356 hits = SWAP_RA_HITS(ra_val);
357 if (readahead)
358 hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
359 atomic_long_set(v: &vma->swap_readahead_info,
360 SWAP_RA_VAL(addr, win, hits));
361 }
362
363 if (readahead) {
364 count_vm_event(item: SWAP_RA_HIT);
365 if (!vma || !vma_ra)
366 atomic_inc(v: &swapin_readahead_hits);
367 }
368 } else {
369 folio = NULL;
370 }
371
372 return folio;
373}
374
375/**
376 * filemap_get_incore_folio - Find and get a folio from the page or swap caches.
377 * @mapping: The address_space to search.
378 * @index: The page cache index.
379 *
380 * This differs from filemap_get_folio() in that it will also look for the
381 * folio in the swap cache.
382 *
383 * Return: The found folio or %NULL.
384 */
385struct folio *filemap_get_incore_folio(struct address_space *mapping,
386 pgoff_t index)
387{
388 swp_entry_t swp;
389 struct swap_info_struct *si;
390 struct folio *folio = filemap_get_entry(mapping, index);
391
392 if (!folio)
393 return ERR_PTR(error: -ENOENT);
394 if (!xa_is_value(entry: folio))
395 return folio;
396 if (!shmem_mapping(mapping))
397 return ERR_PTR(error: -ENOENT);
398
399 swp = radix_to_swp_entry(arg: folio);
400 /* There might be swapin error entries in shmem mapping. */
401 if (non_swap_entry(entry: swp))
402 return ERR_PTR(error: -ENOENT);
403 /* Prevent swapoff from happening to us */
404 si = get_swap_device(entry: swp);
405 if (!si)
406 return ERR_PTR(error: -ENOENT);
407 index = swp_offset(entry: swp);
408 folio = filemap_get_folio(swap_address_space(swp), index);
409 put_swap_device(si);
410 return folio;
411}
412
413struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
414 struct mempolicy *mpol, pgoff_t ilx,
415 bool *new_page_allocated)
416{
417 struct swap_info_struct *si;
418 struct folio *folio;
419 struct page *page;
420 void *shadow = NULL;
421
422 *new_page_allocated = false;
423 si = get_swap_device(entry);
424 if (!si)
425 return NULL;
426
427 for (;;) {
428 int err;
429 /*
430 * First check the swap cache. Since this is normally
431 * called after swap_cache_get_folio() failed, re-calling
432 * that would confuse statistics.
433 */
434 folio = filemap_get_folio(swap_address_space(entry),
435 index: swp_offset(entry));
436 if (!IS_ERR(ptr: folio)) {
437 page = folio_file_page(folio, index: swp_offset(entry));
438 goto got_page;
439 }
440
441 /*
442 * Just skip read ahead for unused swap slot.
443 * During swap_off when swap_slot_cache is disabled,
444 * we have to handle the race between putting
445 * swap entry in swap cache and marking swap slot
446 * as SWAP_HAS_CACHE. That's done in later part of code or
447 * else swap_off will be aborted if we return NULL.
448 */
449 if (!swap_swapcount(si, entry) && swap_slot_cache_enabled)
450 goto fail_put_swap;
451
452 /*
453 * Get a new page to read into from swap. Allocate it now,
454 * before marking swap_map SWAP_HAS_CACHE, when -EEXIST will
455 * cause any racers to loop around until we add it to cache.
456 */
457 folio = (struct folio *)alloc_pages_mpol(gfp: gfp_mask, order: 0,
458 mpol, ilx, nid: numa_node_id());
459 if (!folio)
460 goto fail_put_swap;
461
462 /*
463 * Swap entry may have been freed since our caller observed it.
464 */
465 err = swapcache_prepare(entry);
466 if (!err)
467 break;
468
469 folio_put(folio);
470 if (err != -EEXIST)
471 goto fail_put_swap;
472
473 /*
474 * We might race against __delete_from_swap_cache(), and
475 * stumble across a swap_map entry whose SWAP_HAS_CACHE
476 * has not yet been cleared. Or race against another
477 * __read_swap_cache_async(), which has set SWAP_HAS_CACHE
478 * in swap_map, but not yet added its page to swap cache.
479 */
480 schedule_timeout_uninterruptible(timeout: 1);
481 }
482
483 /*
484 * The swap entry is ours to swap in. Prepare the new page.
485 */
486
487 __folio_set_locked(folio);
488 __folio_set_swapbacked(folio);
489
490 if (mem_cgroup_swapin_charge_folio(folio, NULL, gfp: gfp_mask, entry))
491 goto fail_unlock;
492
493 /* May fail (-ENOMEM) if XArray node allocation failed. */
494 if (add_to_swap_cache(folio, entry, gfp: gfp_mask & GFP_RECLAIM_MASK, shadowp: &shadow))
495 goto fail_unlock;
496
497 mem_cgroup_swapin_uncharge_swap(entry);
498
499 if (shadow)
500 workingset_refault(folio, shadow);
501
502 /* Caller will initiate read into locked folio */
503 folio_add_lru(folio);
504 *new_page_allocated = true;
505 page = &folio->page;
506got_page:
507 put_swap_device(si);
508 return page;
509
510fail_unlock:
511 put_swap_folio(folio, entry);
512 folio_unlock(folio);
513 folio_put(folio);
514fail_put_swap:
515 put_swap_device(si);
516 return NULL;
517}
518
519/*
520 * Locate a page of swap in physical memory, reserving swap cache space
521 * and reading the disk if it is not already cached.
522 * A failure return means that either the page allocation failed or that
523 * the swap entry is no longer in use.
524 *
525 * get/put_swap_device() aren't needed to call this function, because
526 * __read_swap_cache_async() call them and swap_readpage() holds the
527 * swap cache folio lock.
528 */
529struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
530 struct vm_area_struct *vma,
531 unsigned long addr, struct swap_iocb **plug)
532{
533 bool page_allocated;
534 struct mempolicy *mpol;
535 pgoff_t ilx;
536 struct page *page;
537
538 mpol = get_vma_policy(vma, addr, order: 0, ilx: &ilx);
539 page = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
540 new_page_allocated: &page_allocated);
541 mpol_cond_put(pol: mpol);
542
543 if (page_allocated)
544 swap_readpage(page, do_poll: false, plug);
545 return page;
546}
547
548static unsigned int __swapin_nr_pages(unsigned long prev_offset,
549 unsigned long offset,
550 int hits,
551 int max_pages,
552 int prev_win)
553{
554 unsigned int pages, last_ra;
555
556 /*
557 * This heuristic has been found to work well on both sequential and
558 * random loads, swapping to hard disk or to SSD: please don't ask
559 * what the "+ 2" means, it just happens to work well, that's all.
560 */
561 pages = hits + 2;
562 if (pages == 2) {
563 /*
564 * We can have no readahead hits to judge by: but must not get
565 * stuck here forever, so check for an adjacent offset instead
566 * (and don't even bother to check whether swap type is same).
567 */
568 if (offset != prev_offset + 1 && offset != prev_offset - 1)
569 pages = 1;
570 } else {
571 unsigned int roundup = 4;
572 while (roundup < pages)
573 roundup <<= 1;
574 pages = roundup;
575 }
576
577 if (pages > max_pages)
578 pages = max_pages;
579
580 /* Don't shrink readahead too fast */
581 last_ra = prev_win / 2;
582 if (pages < last_ra)
583 pages = last_ra;
584
585 return pages;
586}
587
588static unsigned long swapin_nr_pages(unsigned long offset)
589{
590 static unsigned long prev_offset;
591 unsigned int hits, pages, max_pages;
592 static atomic_t last_readahead_pages;
593
594 max_pages = 1 << READ_ONCE(page_cluster);
595 if (max_pages <= 1)
596 return 1;
597
598 hits = atomic_xchg(v: &swapin_readahead_hits, new: 0);
599 pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits,
600 max_pages,
601 prev_win: atomic_read(v: &last_readahead_pages));
602 if (!hits)
603 WRITE_ONCE(prev_offset, offset);
604 atomic_set(v: &last_readahead_pages, i: pages);
605
606 return pages;
607}
608
609/**
610 * swap_cluster_readahead - swap in pages in hope we need them soon
611 * @entry: swap entry of this memory
612 * @gfp_mask: memory allocation flags
613 * @mpol: NUMA memory allocation policy to be applied
614 * @ilx: NUMA interleave index, for use only when MPOL_INTERLEAVE
615 *
616 * Returns the struct page for entry and addr, after queueing swapin.
617 *
618 * Primitive swap readahead code. We simply read an aligned block of
619 * (1 << page_cluster) entries in the swap area. This method is chosen
620 * because it doesn't cost us any seek time. We also make sure to queue
621 * the 'original' request together with the readahead ones...
622 *
623 * Note: it is intentional that the same NUMA policy and interleave index
624 * are used for every page of the readahead: neighbouring pages on swap
625 * are fairly likely to have been swapped out from the same node.
626 */
627struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
628 struct mempolicy *mpol, pgoff_t ilx)
629{
630 struct page *page;
631 unsigned long entry_offset = swp_offset(entry);
632 unsigned long offset = entry_offset;
633 unsigned long start_offset, end_offset;
634 unsigned long mask;
635 struct swap_info_struct *si = swp_swap_info(entry);
636 struct blk_plug plug;
637 struct swap_iocb *splug = NULL;
638 bool page_allocated;
639
640 mask = swapin_nr_pages(offset) - 1;
641 if (!mask)
642 goto skip;
643
644 /* Read a page_cluster sized and aligned cluster around offset. */
645 start_offset = offset & ~mask;
646 end_offset = offset | mask;
647 if (!start_offset) /* First page is swap header. */
648 start_offset++;
649 if (end_offset >= si->max)
650 end_offset = si->max - 1;
651
652 blk_start_plug(&plug);
653 for (offset = start_offset; offset <= end_offset ; offset++) {
654 /* Ok, do the async read-ahead now */
655 page = __read_swap_cache_async(
656 entry: swp_entry(type: swp_type(entry), offset),
657 gfp_mask, mpol, ilx, new_page_allocated: &page_allocated);
658 if (!page)
659 continue;
660 if (page_allocated) {
661 swap_readpage(page, do_poll: false, plug: &splug);
662 if (offset != entry_offset) {
663 SetPageReadahead(page);
664 count_vm_event(item: SWAP_RA);
665 }
666 }
667 put_page(page);
668 }
669 blk_finish_plug(&plug);
670 swap_read_unplug(plug: splug);
671 lru_add_drain(); /* Push any new pages onto the LRU now */
672skip:
673 /* The page was likely read above, so no need for plugging here */
674 page = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
675 new_page_allocated: &page_allocated);
676 if (unlikely(page_allocated))
677 swap_readpage(page, do_poll: false, NULL);
678 return page;
679}
680
681int init_swap_address_space(unsigned int type, unsigned long nr_pages)
682{
683 struct address_space *spaces, *space;
684 unsigned int i, nr;
685
686 nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
687 spaces = kvcalloc(n: nr, size: sizeof(struct address_space), GFP_KERNEL);
688 if (!spaces)
689 return -ENOMEM;
690 for (i = 0; i < nr; i++) {
691 space = spaces + i;
692 xa_init_flags(xa: &space->i_pages, XA_FLAGS_LOCK_IRQ);
693 atomic_set(v: &space->i_mmap_writable, i: 0);
694 space->a_ops = &swap_aops;
695 /* swap cache doesn't use writeback related tags */
696 mapping_set_no_writeback_tags(mapping: space);
697 }
698 nr_swapper_spaces[type] = nr;
699 swapper_spaces[type] = spaces;
700
701 return 0;
702}
703
704void exit_swap_address_space(unsigned int type)
705{
706 int i;
707 struct address_space *spaces = swapper_spaces[type];
708
709 for (i = 0; i < nr_swapper_spaces[type]; i++)
710 VM_WARN_ON_ONCE(!mapping_empty(&spaces[i]));
711 kvfree(addr: spaces);
712 nr_swapper_spaces[type] = 0;
713 swapper_spaces[type] = NULL;
714}
715
716#define SWAP_RA_ORDER_CEILING 5
717
718struct vma_swap_readahead {
719 unsigned short win;
720 unsigned short offset;
721 unsigned short nr_pte;
722};
723
724static void swap_ra_info(struct vm_fault *vmf,
725 struct vma_swap_readahead *ra_info)
726{
727 struct vm_area_struct *vma = vmf->vma;
728 unsigned long ra_val;
729 unsigned long faddr, pfn, fpfn, lpfn, rpfn;
730 unsigned long start, end;
731 unsigned int max_win, hits, prev_win, win;
732
733 max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
734 SWAP_RA_ORDER_CEILING);
735 if (max_win == 1) {
736 ra_info->win = 1;
737 return;
738 }
739
740 faddr = vmf->address;
741 fpfn = PFN_DOWN(faddr);
742 ra_val = GET_SWAP_RA_VAL(vma);
743 pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
744 prev_win = SWAP_RA_WIN(ra_val);
745 hits = SWAP_RA_HITS(ra_val);
746 ra_info->win = win = __swapin_nr_pages(prev_offset: pfn, offset: fpfn, hits,
747 max_pages: max_win, prev_win);
748 atomic_long_set(v: &vma->swap_readahead_info,
749 SWAP_RA_VAL(faddr, win, 0));
750 if (win == 1)
751 return;
752
753 if (fpfn == pfn + 1) {
754 lpfn = fpfn;
755 rpfn = fpfn + win;
756 } else if (pfn == fpfn + 1) {
757 lpfn = fpfn - win + 1;
758 rpfn = fpfn + 1;
759 } else {
760 unsigned int left = (win - 1) / 2;
761
762 lpfn = fpfn - left;
763 rpfn = fpfn + win - left;
764 }
765 start = max3(lpfn, PFN_DOWN(vma->vm_start),
766 PFN_DOWN(faddr & PMD_MASK));
767 end = min3(rpfn, PFN_DOWN(vma->vm_end),
768 PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
769
770 ra_info->nr_pte = end - start;
771 ra_info->offset = fpfn - start;
772}
773
774/**
775 * swap_vma_readahead - swap in pages in hope we need them soon
776 * @targ_entry: swap entry of the targeted memory
777 * @gfp_mask: memory allocation flags
778 * @mpol: NUMA memory allocation policy to be applied
779 * @targ_ilx: NUMA interleave index, for use only when MPOL_INTERLEAVE
780 * @vmf: fault information
781 *
782 * Returns the struct page for entry and addr, after queueing swapin.
783 *
784 * Primitive swap readahead code. We simply read in a few pages whose
785 * virtual addresses are around the fault address in the same vma.
786 *
787 * Caller must hold read mmap_lock if vmf->vma is not NULL.
788 *
789 */
790static struct page *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
791 struct mempolicy *mpol, pgoff_t targ_ilx,
792 struct vm_fault *vmf)
793{
794 struct blk_plug plug;
795 struct swap_iocb *splug = NULL;
796 struct page *page;
797 pte_t *pte = NULL, pentry;
798 unsigned long addr;
799 swp_entry_t entry;
800 pgoff_t ilx;
801 unsigned int i;
802 bool page_allocated;
803 struct vma_swap_readahead ra_info = {
804 .win = 1,
805 };
806
807 swap_ra_info(vmf, ra_info: &ra_info);
808 if (ra_info.win == 1)
809 goto skip;
810
811 addr = vmf->address - (ra_info.offset * PAGE_SIZE);
812 ilx = targ_ilx - ra_info.offset;
813
814 blk_start_plug(&plug);
815 for (i = 0; i < ra_info.nr_pte; i++, ilx++, addr += PAGE_SIZE) {
816 if (!pte++) {
817 pte = pte_offset_map(pmd: vmf->pmd, addr);
818 if (!pte)
819 break;
820 }
821 pentry = ptep_get_lockless(ptep: pte);
822 if (!is_swap_pte(pte: pentry))
823 continue;
824 entry = pte_to_swp_entry(pte: pentry);
825 if (unlikely(non_swap_entry(entry)))
826 continue;
827 pte_unmap(pte);
828 pte = NULL;
829 page = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
830 new_page_allocated: &page_allocated);
831 if (!page)
832 continue;
833 if (page_allocated) {
834 swap_readpage(page, do_poll: false, plug: &splug);
835 if (i != ra_info.offset) {
836 SetPageReadahead(page);
837 count_vm_event(item: SWAP_RA);
838 }
839 }
840 put_page(page);
841 }
842 if (pte)
843 pte_unmap(pte);
844 blk_finish_plug(&plug);
845 swap_read_unplug(plug: splug);
846 lru_add_drain();
847skip:
848 /* The page was likely read above, so no need for plugging here */
849 page = __read_swap_cache_async(entry: targ_entry, gfp_mask, mpol, ilx: targ_ilx,
850 new_page_allocated: &page_allocated);
851 if (unlikely(page_allocated))
852 swap_readpage(page, do_poll: false, NULL);
853 return page;
854}
855
856/**
857 * swapin_readahead - swap in pages in hope we need them soon
858 * @entry: swap entry of this memory
859 * @gfp_mask: memory allocation flags
860 * @vmf: fault information
861 *
862 * Returns the struct page for entry and addr, after queueing swapin.
863 *
864 * It's a main entry function for swap readahead. By the configuration,
865 * it will read ahead blocks by cluster-based(ie, physical disk based)
866 * or vma-based(ie, virtual address based on faulty address) readahead.
867 */
868struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
869 struct vm_fault *vmf)
870{
871 struct mempolicy *mpol;
872 pgoff_t ilx;
873 struct page *page;
874
875 mpol = get_vma_policy(vma: vmf->vma, addr: vmf->address, order: 0, ilx: &ilx);
876 page = swap_use_vma_readahead() ?
877 swap_vma_readahead(targ_entry: entry, gfp_mask, mpol, targ_ilx: ilx, vmf) :
878 swap_cluster_readahead(entry, gfp_mask, mpol, ilx);
879 mpol_cond_put(pol: mpol);
880 return page;
881}
882
883#ifdef CONFIG_SYSFS
884static ssize_t vma_ra_enabled_show(struct kobject *kobj,
885 struct kobj_attribute *attr, char *buf)
886{
887 return sysfs_emit(buf, fmt: "%s\n",
888 enable_vma_readahead ? "true" : "false");
889}
890static ssize_t vma_ra_enabled_store(struct kobject *kobj,
891 struct kobj_attribute *attr,
892 const char *buf, size_t count)
893{
894 ssize_t ret;
895
896 ret = kstrtobool(s: buf, res: &enable_vma_readahead);
897 if (ret)
898 return ret;
899
900 return count;
901}
902static struct kobj_attribute vma_ra_enabled_attr = __ATTR_RW(vma_ra_enabled);
903
904static struct attribute *swap_attrs[] = {
905 &vma_ra_enabled_attr.attr,
906 NULL,
907};
908
909static const struct attribute_group swap_attr_group = {
910 .attrs = swap_attrs,
911};
912
913static int __init swap_init_sysfs(void)
914{
915 int err;
916 struct kobject *swap_kobj;
917
918 swap_kobj = kobject_create_and_add(name: "swap", parent: mm_kobj);
919 if (!swap_kobj) {
920 pr_err("failed to create swap kobject\n");
921 return -ENOMEM;
922 }
923 err = sysfs_create_group(kobj: swap_kobj, grp: &swap_attr_group);
924 if (err) {
925 pr_err("failed to register swap group\n");
926 goto delete_obj;
927 }
928 return 0;
929
930delete_obj:
931 kobject_put(kobj: swap_kobj);
932 return err;
933}
934subsys_initcall(swap_init_sysfs);
935#endif
936

source code of linux/mm/swap_state.c