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/migrate.h>
20 #include <linux/vmalloc.h>
21 #include <linux/swap_slots.h>
22 #include <linux/huge_mm.h>
23 #include <linux/shmem_fs.h>
24 #include "internal.h"
25 #include "swap.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 .dirty_folio = noop_dirty_folio,
34 #ifdef CONFIG_MIGRATION
35 .migrate_folio = migrate_folio,
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 static bool enable_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 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
62
show_swap_cache_info(void)63 void show_swap_cache_info(void)
64 {
65 printk("%lu pages in swap cache\n", total_swapcache_pages());
66 printk("Free swap = %ldkB\n", K(get_nr_swap_pages()));
67 printk("Total swap = %lukB\n", K(total_swap_pages));
68 }
69
get_shadow_from_swap_cache(swp_entry_t entry)70 void *get_shadow_from_swap_cache(swp_entry_t entry)
71 {
72 struct address_space *address_space = swap_address_space(entry);
73 pgoff_t idx = swp_offset(entry);
74 struct page *page;
75
76 page = xa_load(&address_space->i_pages, idx);
77 if (xa_is_value(page))
78 return page;
79 return NULL;
80 }
81
82 /*
83 * add_to_swap_cache resembles filemap_add_folio on swapper_space,
84 * but sets SwapCache flag and private instead of mapping and index.
85 */
add_to_swap_cache(struct folio * folio,swp_entry_t entry,gfp_t gfp,void ** shadowp)86 int add_to_swap_cache(struct folio *folio, swp_entry_t entry,
87 gfp_t gfp, void **shadowp)
88 {
89 struct address_space *address_space = swap_address_space(entry);
90 pgoff_t idx = swp_offset(entry);
91 XA_STATE_ORDER(xas, &address_space->i_pages, idx, folio_order(folio));
92 unsigned long i, nr = folio_nr_pages(folio);
93 void *old;
94
95 xas_set_update(&xas, workingset_update_node);
96
97 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
98 VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio);
99 VM_BUG_ON_FOLIO(!folio_test_swapbacked(folio), folio);
100
101 folio_ref_add(folio, nr);
102 folio_set_swapcache(folio);
103 folio->swap = entry;
104
105 do {
106 xas_lock_irq(&xas);
107 xas_create_range(&xas);
108 if (xas_error(&xas))
109 goto unlock;
110 for (i = 0; i < nr; i++) {
111 VM_BUG_ON_FOLIO(xas.xa_index != idx + i, folio);
112 old = xas_load(&xas);
113 if (xa_is_value(old)) {
114 if (shadowp)
115 *shadowp = old;
116 }
117 xas_store(&xas, folio);
118 xas_next(&xas);
119 }
120 address_space->nrpages += nr;
121 __node_stat_mod_folio(folio, NR_FILE_PAGES, nr);
122 __lruvec_stat_mod_folio(folio, NR_SWAPCACHE, nr);
123 unlock:
124 xas_unlock_irq(&xas);
125 } while (xas_nomem(&xas, gfp));
126
127 if (!xas_error(&xas))
128 return 0;
129
130 folio_clear_swapcache(folio);
131 folio_ref_sub(folio, nr);
132 return xas_error(&xas);
133 }
134
135 /*
136 * This must be called only on folios that have
137 * been verified to be in the swap cache.
138 */
__delete_from_swap_cache(struct folio * folio,swp_entry_t entry,void * shadow)139 void __delete_from_swap_cache(struct folio *folio,
140 swp_entry_t entry, void *shadow)
141 {
142 struct address_space *address_space = swap_address_space(entry);
143 int i;
144 long nr = folio_nr_pages(folio);
145 pgoff_t idx = swp_offset(entry);
146 XA_STATE(xas, &address_space->i_pages, idx);
147
148 xas_set_update(&xas, workingset_update_node);
149
150 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
151 VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
152 VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio);
153
154 for (i = 0; i < nr; i++) {
155 void *entry = xas_store(&xas, shadow);
156 VM_BUG_ON_PAGE(entry != folio, entry);
157 xas_next(&xas);
158 }
159 folio->swap.val = 0;
160 folio_clear_swapcache(folio);
161 address_space->nrpages -= nr;
162 __node_stat_mod_folio(folio, NR_FILE_PAGES, -nr);
163 __lruvec_stat_mod_folio(folio, NR_SWAPCACHE, -nr);
164 }
165
166 /**
167 * add_to_swap - allocate swap space for a folio
168 * @folio: folio we want to move to swap
169 *
170 * Allocate swap space for the folio and add the folio to the
171 * swap cache.
172 *
173 * Context: Caller needs to hold the folio lock.
174 * Return: Whether the folio was added to the swap cache.
175 */
add_to_swap(struct folio * folio)176 bool add_to_swap(struct folio *folio)
177 {
178 swp_entry_t entry;
179 int err;
180
181 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
182 VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);
183
184 entry = folio_alloc_swap(folio);
185 if (!entry.val)
186 return false;
187
188 /*
189 * XArray node allocations from PF_MEMALLOC contexts could
190 * completely exhaust the page allocator. __GFP_NOMEMALLOC
191 * stops emergency reserves from being allocated.
192 *
193 * TODO: this could cause a theoretical memory reclaim
194 * deadlock in the swap out path.
195 */
196 /*
197 * Add it to the swap cache.
198 */
199 err = add_to_swap_cache(folio, entry,
200 __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN, NULL);
201 if (err)
202 /*
203 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
204 * clear SWAP_HAS_CACHE flag.
205 */
206 goto fail;
207 /*
208 * Normally the folio will be dirtied in unmap because its
209 * pte should be dirty. A special case is MADV_FREE page. The
210 * page's pte could have dirty bit cleared but the folio's
211 * SwapBacked flag is still set because clearing the dirty bit
212 * and SwapBacked flag has no lock protected. For such folio,
213 * unmap will not set dirty bit for it, so folio reclaim will
214 * not write the folio out. This can cause data corruption when
215 * the folio is swapped in later. Always setting the dirty flag
216 * for the folio solves the problem.
217 */
218 folio_mark_dirty(folio);
219
220 return true;
221
222 fail:
223 put_swap_folio(folio, entry);
224 return false;
225 }
226
227 /*
228 * This must be called only on folios that have
229 * been verified to be in the swap cache and locked.
230 * It will never put the folio into the free list,
231 * the caller has a reference on the folio.
232 */
delete_from_swap_cache(struct folio * folio)233 void delete_from_swap_cache(struct folio *folio)
234 {
235 swp_entry_t entry = folio->swap;
236 struct address_space *address_space = swap_address_space(entry);
237
238 xa_lock_irq(&address_space->i_pages);
239 __delete_from_swap_cache(folio, entry, NULL);
240 xa_unlock_irq(&address_space->i_pages);
241
242 put_swap_folio(folio, entry);
243 folio_ref_sub(folio, folio_nr_pages(folio));
244 }
245
clear_shadow_from_swap_cache(int type,unsigned long begin,unsigned long end)246 void clear_shadow_from_swap_cache(int type, unsigned long begin,
247 unsigned long end)
248 {
249 unsigned long curr = begin;
250 void *old;
251
252 for (;;) {
253 swp_entry_t entry = swp_entry(type, curr);
254 struct address_space *address_space = swap_address_space(entry);
255 XA_STATE(xas, &address_space->i_pages, curr);
256
257 xas_set_update(&xas, workingset_update_node);
258
259 xa_lock_irq(&address_space->i_pages);
260 xas_for_each(&xas, old, end) {
261 if (!xa_is_value(old))
262 continue;
263 xas_store(&xas, NULL);
264 }
265 xa_unlock_irq(&address_space->i_pages);
266
267 /* search the next swapcache until we meet end */
268 curr >>= SWAP_ADDRESS_SPACE_SHIFT;
269 curr++;
270 curr <<= SWAP_ADDRESS_SPACE_SHIFT;
271 if (curr > end)
272 break;
273 }
274 }
275
276 /*
277 * If we are the only user, then try to free up the swap cache.
278 *
279 * Its ok to check the swapcache flag without the folio lock
280 * here because we are going to recheck again inside
281 * folio_free_swap() _with_ the lock.
282 * - Marcelo
283 */
free_swap_cache(struct page * page)284 void free_swap_cache(struct page *page)
285 {
286 struct folio *folio = page_folio(page);
287
288 if (folio_test_swapcache(folio) && !folio_mapped(folio) &&
289 folio_trylock(folio)) {
290 folio_free_swap(folio);
291 folio_unlock(folio);
292 }
293 }
294
295 /*
296 * Perform a free_page(), also freeing any swap cache associated with
297 * this page if it is the last user of the page.
298 */
free_page_and_swap_cache(struct page * page)299 void free_page_and_swap_cache(struct page *page)
300 {
301 free_swap_cache(page);
302 if (!is_huge_zero_page(page))
303 put_page(page);
304 }
305
306 /*
307 * Passed an array of pages, drop them all from swapcache and then release
308 * them. They are removed from the LRU and freed if this is their last use.
309 */
free_pages_and_swap_cache(struct encoded_page ** pages,int nr)310 void free_pages_and_swap_cache(struct encoded_page **pages, int nr)
311 {
312 lru_add_drain();
313 for (int i = 0; i < nr; i++)
314 free_swap_cache(encoded_page_ptr(pages[i]));
315 release_pages(pages, nr);
316 }
317
swap_use_vma_readahead(void)318 static inline bool swap_use_vma_readahead(void)
319 {
320 return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
321 }
322
323 /*
324 * Lookup a swap entry in the swap cache. A found folio will be returned
325 * unlocked and with its refcount incremented - we rely on the kernel
326 * lock getting page table operations atomic even if we drop the folio
327 * lock before returning.
328 *
329 * Caller must lock the swap device or hold a reference to keep it valid.
330 */
swap_cache_get_folio(swp_entry_t entry,struct vm_area_struct * vma,unsigned long addr)331 struct folio *swap_cache_get_folio(swp_entry_t entry,
332 struct vm_area_struct *vma, unsigned long addr)
333 {
334 struct folio *folio;
335
336 folio = filemap_get_folio(swap_address_space(entry), swp_offset(entry));
337 if (!IS_ERR(folio)) {
338 bool vma_ra = swap_use_vma_readahead();
339 bool readahead;
340
341 /*
342 * At the moment, we don't support PG_readahead for anon THP
343 * so let's bail out rather than confusing the readahead stat.
344 */
345 if (unlikely(folio_test_large(folio)))
346 return folio;
347
348 readahead = folio_test_clear_readahead(folio);
349 if (vma && vma_ra) {
350 unsigned long ra_val;
351 int win, hits;
352
353 ra_val = GET_SWAP_RA_VAL(vma);
354 win = SWAP_RA_WIN(ra_val);
355 hits = SWAP_RA_HITS(ra_val);
356 if (readahead)
357 hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
358 atomic_long_set(&vma->swap_readahead_info,
359 SWAP_RA_VAL(addr, win, hits));
360 }
361
362 if (readahead) {
363 count_vm_event(SWAP_RA_HIT);
364 if (!vma || !vma_ra)
365 atomic_inc(&swapin_readahead_hits);
366 }
367 } else {
368 folio = NULL;
369 }
370
371 return folio;
372 }
373
374 /**
375 * filemap_get_incore_folio - Find and get a folio from the page or swap caches.
376 * @mapping: The address_space to search.
377 * @index: The page cache index.
378 *
379 * This differs from filemap_get_folio() in that it will also look for the
380 * folio in the swap cache.
381 *
382 * Return: The found folio or %NULL.
383 */
filemap_get_incore_folio(struct address_space * mapping,pgoff_t index)384 struct folio *filemap_get_incore_folio(struct address_space *mapping,
385 pgoff_t index)
386 {
387 swp_entry_t swp;
388 struct swap_info_struct *si;
389 struct folio *folio = filemap_get_entry(mapping, index);
390
391 if (!folio)
392 return ERR_PTR(-ENOENT);
393 if (!xa_is_value(folio))
394 return folio;
395 if (!shmem_mapping(mapping))
396 return ERR_PTR(-ENOENT);
397
398 swp = radix_to_swp_entry(folio);
399 /* There might be swapin error entries in shmem mapping. */
400 if (non_swap_entry(swp))
401 return ERR_PTR(-ENOENT);
402 /* Prevent swapoff from happening to us */
403 si = get_swap_device(swp);
404 if (!si)
405 return ERR_PTR(-ENOENT);
406 index = swp_offset(swp);
407 folio = filemap_get_folio(swap_address_space(swp), index);
408 put_swap_device(si);
409 return folio;
410 }
411
__read_swap_cache_async(swp_entry_t entry,gfp_t gfp_mask,struct vm_area_struct * vma,unsigned long addr,bool * new_page_allocated)412 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
413 struct vm_area_struct *vma, unsigned long addr,
414 bool *new_page_allocated)
415 {
416 struct swap_info_struct *si;
417 struct folio *folio;
418 struct page *page;
419 void *shadow = NULL;
420
421 *new_page_allocated = false;
422 si = get_swap_device(entry);
423 if (!si)
424 return NULL;
425
426 for (;;) {
427 int err;
428 /*
429 * First check the swap cache. Since this is normally
430 * called after swap_cache_get_folio() failed, re-calling
431 * that would confuse statistics.
432 */
433 folio = filemap_get_folio(swap_address_space(entry),
434 swp_offset(entry));
435 if (!IS_ERR(folio)) {
436 page = folio_file_page(folio, swp_offset(entry));
437 goto got_page;
438 }
439
440 /*
441 * Just skip read ahead for unused swap slot.
442 * During swap_off when swap_slot_cache is disabled,
443 * we have to handle the race between putting
444 * swap entry in swap cache and marking swap slot
445 * as SWAP_HAS_CACHE. That's done in later part of code or
446 * else swap_off will be aborted if we return NULL.
447 */
448 if (!swap_swapcount(si, entry) && swap_slot_cache_enabled)
449 goto fail_put_swap;
450
451 /*
452 * Get a new page to read into from swap. Allocate it now,
453 * before marking swap_map SWAP_HAS_CACHE, when -EEXIST will
454 * cause any racers to loop around until we add it to cache.
455 */
456 folio = vma_alloc_folio(gfp_mask, 0, vma, addr, false);
457 if (!folio)
458 goto fail_put_swap;
459
460 /*
461 * Swap entry may have been freed since our caller observed it.
462 */
463 err = swapcache_prepare(entry);
464 if (!err)
465 break;
466
467 folio_put(folio);
468 if (err != -EEXIST)
469 goto fail_put_swap;
470
471 /*
472 * We might race against __delete_from_swap_cache(), and
473 * stumble across a swap_map entry whose SWAP_HAS_CACHE
474 * has not yet been cleared. Or race against another
475 * __read_swap_cache_async(), which has set SWAP_HAS_CACHE
476 * in swap_map, but not yet added its page to swap cache.
477 */
478 schedule_timeout_uninterruptible(1);
479 }
480
481 /*
482 * The swap entry is ours to swap in. Prepare the new page.
483 */
484
485 __folio_set_locked(folio);
486 __folio_set_swapbacked(folio);
487
488 if (mem_cgroup_swapin_charge_folio(folio, NULL, gfp_mask, entry))
489 goto fail_unlock;
490
491 /* May fail (-ENOMEM) if XArray node allocation failed. */
492 if (add_to_swap_cache(folio, entry, gfp_mask & GFP_RECLAIM_MASK, &shadow))
493 goto fail_unlock;
494
495 mem_cgroup_swapin_uncharge_swap(entry);
496
497 if (shadow)
498 workingset_refault(folio, shadow);
499
500 /* Caller will initiate read into locked folio */
501 folio_add_lru(folio);
502 *new_page_allocated = true;
503 page = &folio->page;
504 got_page:
505 put_swap_device(si);
506 return page;
507
508 fail_unlock:
509 put_swap_folio(folio, entry);
510 folio_unlock(folio);
511 folio_put(folio);
512 fail_put_swap:
513 put_swap_device(si);
514 return NULL;
515 }
516
517 /*
518 * Locate a page of swap in physical memory, reserving swap cache space
519 * and reading the disk if it is not already cached.
520 * A failure return means that either the page allocation failed or that
521 * the swap entry is no longer in use.
522 *
523 * get/put_swap_device() aren't needed to call this function, because
524 * __read_swap_cache_async() call them and swap_readpage() holds the
525 * swap cache folio lock.
526 */
read_swap_cache_async(swp_entry_t entry,gfp_t gfp_mask,struct vm_area_struct * vma,unsigned long addr,struct swap_iocb ** plug)527 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
528 struct vm_area_struct *vma,
529 unsigned long addr, struct swap_iocb **plug)
530 {
531 bool page_was_allocated;
532 struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
533 vma, addr, &page_was_allocated);
534
535 if (page_was_allocated)
536 swap_readpage(retpage, false, plug);
537
538 return retpage;
539 }
540
__swapin_nr_pages(unsigned long prev_offset,unsigned long offset,int hits,int max_pages,int prev_win)541 static unsigned int __swapin_nr_pages(unsigned long prev_offset,
542 unsigned long offset,
543 int hits,
544 int max_pages,
545 int prev_win)
546 {
547 unsigned int pages, last_ra;
548
549 /*
550 * This heuristic has been found to work well on both sequential and
551 * random loads, swapping to hard disk or to SSD: please don't ask
552 * what the "+ 2" means, it just happens to work well, that's all.
553 */
554 pages = hits + 2;
555 if (pages == 2) {
556 /*
557 * We can have no readahead hits to judge by: but must not get
558 * stuck here forever, so check for an adjacent offset instead
559 * (and don't even bother to check whether swap type is same).
560 */
561 if (offset != prev_offset + 1 && offset != prev_offset - 1)
562 pages = 1;
563 } else {
564 unsigned int roundup = 4;
565 while (roundup < pages)
566 roundup <<= 1;
567 pages = roundup;
568 }
569
570 if (pages > max_pages)
571 pages = max_pages;
572
573 /* Don't shrink readahead too fast */
574 last_ra = prev_win / 2;
575 if (pages < last_ra)
576 pages = last_ra;
577
578 return pages;
579 }
580
swapin_nr_pages(unsigned long offset)581 static unsigned long swapin_nr_pages(unsigned long offset)
582 {
583 static unsigned long prev_offset;
584 unsigned int hits, pages, max_pages;
585 static atomic_t last_readahead_pages;
586
587 max_pages = 1 << READ_ONCE(page_cluster);
588 if (max_pages <= 1)
589 return 1;
590
591 hits = atomic_xchg(&swapin_readahead_hits, 0);
592 pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits,
593 max_pages,
594 atomic_read(&last_readahead_pages));
595 if (!hits)
596 WRITE_ONCE(prev_offset, offset);
597 atomic_set(&last_readahead_pages, pages);
598
599 return pages;
600 }
601
602 /**
603 * swap_cluster_readahead - swap in pages in hope we need them soon
604 * @entry: swap entry of this memory
605 * @gfp_mask: memory allocation flags
606 * @vmf: fault information
607 *
608 * Returns the struct page for entry and addr, after queueing swapin.
609 *
610 * Primitive swap readahead code. We simply read an aligned block of
611 * (1 << page_cluster) entries in the swap area. This method is chosen
612 * because it doesn't cost us any seek time. We also make sure to queue
613 * the 'original' request together with the readahead ones...
614 *
615 * This has been extended to use the NUMA policies from the mm triggering
616 * the readahead.
617 *
618 * Caller must hold read mmap_lock if vmf->vma is not NULL.
619 */
swap_cluster_readahead(swp_entry_t entry,gfp_t gfp_mask,struct vm_fault * vmf)620 struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
621 struct vm_fault *vmf)
622 {
623 struct page *page;
624 unsigned long entry_offset = swp_offset(entry);
625 unsigned long offset = entry_offset;
626 unsigned long start_offset, end_offset;
627 unsigned long mask;
628 struct swap_info_struct *si = swp_swap_info(entry);
629 struct blk_plug plug;
630 struct swap_iocb *splug = NULL;
631 bool page_allocated;
632 struct vm_area_struct *vma = vmf->vma;
633 unsigned long addr = vmf->address;
634
635 mask = swapin_nr_pages(offset) - 1;
636 if (!mask)
637 goto skip;
638
639 /* Read a page_cluster sized and aligned cluster around offset. */
640 start_offset = offset & ~mask;
641 end_offset = offset | mask;
642 if (!start_offset) /* First page is swap header. */
643 start_offset++;
644 if (end_offset >= si->max)
645 end_offset = si->max - 1;
646
647 blk_start_plug(&plug);
648 for (offset = start_offset; offset <= end_offset ; offset++) {
649 /* Ok, do the async read-ahead now */
650 page = __read_swap_cache_async(
651 swp_entry(swp_type(entry), offset),
652 gfp_mask, vma, addr, &page_allocated);
653 if (!page)
654 continue;
655 if (page_allocated) {
656 swap_readpage(page, false, &splug);
657 if (offset != entry_offset) {
658 SetPageReadahead(page);
659 count_vm_event(SWAP_RA);
660 }
661 }
662 put_page(page);
663 }
664 blk_finish_plug(&plug);
665 swap_read_unplug(splug);
666
667 lru_add_drain(); /* Push any new pages onto the LRU now */
668 skip:
669 /* The page was likely read above, so no need for plugging here */
670 return read_swap_cache_async(entry, gfp_mask, vma, addr, NULL);
671 }
672
init_swap_address_space(unsigned int type,unsigned long nr_pages)673 int init_swap_address_space(unsigned int type, unsigned long nr_pages)
674 {
675 struct address_space *spaces, *space;
676 unsigned int i, nr;
677
678 nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
679 spaces = kvcalloc(nr, sizeof(struct address_space), GFP_KERNEL);
680 if (!spaces)
681 return -ENOMEM;
682 for (i = 0; i < nr; i++) {
683 space = spaces + i;
684 xa_init_flags(&space->i_pages, XA_FLAGS_LOCK_IRQ);
685 atomic_set(&space->i_mmap_writable, 0);
686 space->a_ops = &swap_aops;
687 /* swap cache doesn't use writeback related tags */
688 mapping_set_no_writeback_tags(space);
689 }
690 nr_swapper_spaces[type] = nr;
691 swapper_spaces[type] = spaces;
692
693 return 0;
694 }
695
exit_swap_address_space(unsigned int type)696 void exit_swap_address_space(unsigned int type)
697 {
698 int i;
699 struct address_space *spaces = swapper_spaces[type];
700
701 for (i = 0; i < nr_swapper_spaces[type]; i++)
702 VM_WARN_ON_ONCE(!mapping_empty(&spaces[i]));
703 kvfree(spaces);
704 nr_swapper_spaces[type] = 0;
705 swapper_spaces[type] = NULL;
706 }
707
708 #define SWAP_RA_ORDER_CEILING 5
709
710 struct vma_swap_readahead {
711 unsigned short win;
712 unsigned short offset;
713 unsigned short nr_pte;
714 };
715
swap_ra_info(struct vm_fault * vmf,struct vma_swap_readahead * ra_info)716 static void swap_ra_info(struct vm_fault *vmf,
717 struct vma_swap_readahead *ra_info)
718 {
719 struct vm_area_struct *vma = vmf->vma;
720 unsigned long ra_val;
721 unsigned long faddr, pfn, fpfn, lpfn, rpfn;
722 unsigned long start, end;
723 unsigned int max_win, hits, prev_win, win;
724
725 max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
726 SWAP_RA_ORDER_CEILING);
727 if (max_win == 1) {
728 ra_info->win = 1;
729 return;
730 }
731
732 faddr = vmf->address;
733 fpfn = PFN_DOWN(faddr);
734 ra_val = GET_SWAP_RA_VAL(vma);
735 pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
736 prev_win = SWAP_RA_WIN(ra_val);
737 hits = SWAP_RA_HITS(ra_val);
738 ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits,
739 max_win, prev_win);
740 atomic_long_set(&vma->swap_readahead_info,
741 SWAP_RA_VAL(faddr, win, 0));
742 if (win == 1)
743 return;
744
745 if (fpfn == pfn + 1) {
746 lpfn = fpfn;
747 rpfn = fpfn + win;
748 } else if (pfn == fpfn + 1) {
749 lpfn = fpfn - win + 1;
750 rpfn = fpfn + 1;
751 } else {
752 unsigned int left = (win - 1) / 2;
753
754 lpfn = fpfn - left;
755 rpfn = fpfn + win - left;
756 }
757 start = max3(lpfn, PFN_DOWN(vma->vm_start),
758 PFN_DOWN(faddr & PMD_MASK));
759 end = min3(rpfn, PFN_DOWN(vma->vm_end),
760 PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
761
762 ra_info->nr_pte = end - start;
763 ra_info->offset = fpfn - start;
764 }
765
766 /**
767 * swap_vma_readahead - swap in pages in hope we need them soon
768 * @fentry: swap entry of this memory
769 * @gfp_mask: memory allocation flags
770 * @vmf: fault information
771 *
772 * Returns the struct page for entry and addr, after queueing swapin.
773 *
774 * Primitive swap readahead code. We simply read in a few pages whose
775 * virtual addresses are around the fault address in the same vma.
776 *
777 * Caller must hold read mmap_lock if vmf->vma is not NULL.
778 *
779 */
swap_vma_readahead(swp_entry_t fentry,gfp_t gfp_mask,struct vm_fault * vmf)780 static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask,
781 struct vm_fault *vmf)
782 {
783 struct blk_plug plug;
784 struct swap_iocb *splug = NULL;
785 struct vm_area_struct *vma = vmf->vma;
786 struct page *page;
787 pte_t *pte = NULL, pentry;
788 unsigned long addr;
789 swp_entry_t entry;
790 unsigned int i;
791 bool page_allocated;
792 struct vma_swap_readahead ra_info = {
793 .win = 1,
794 };
795
796 swap_ra_info(vmf, &ra_info);
797 if (ra_info.win == 1)
798 goto skip;
799
800 addr = vmf->address - (ra_info.offset * PAGE_SIZE);
801
802 blk_start_plug(&plug);
803 for (i = 0; i < ra_info.nr_pte; i++, addr += PAGE_SIZE) {
804 if (!pte++) {
805 pte = pte_offset_map(vmf->pmd, addr);
806 if (!pte)
807 break;
808 }
809 pentry = ptep_get_lockless(pte);
810 if (!is_swap_pte(pentry))
811 continue;
812 entry = pte_to_swp_entry(pentry);
813 if (unlikely(non_swap_entry(entry)))
814 continue;
815 pte_unmap(pte);
816 pte = NULL;
817 page = __read_swap_cache_async(entry, gfp_mask, vma,
818 addr, &page_allocated);
819 if (!page)
820 continue;
821 if (page_allocated) {
822 swap_readpage(page, false, &splug);
823 if (i != ra_info.offset) {
824 SetPageReadahead(page);
825 count_vm_event(SWAP_RA);
826 }
827 }
828 put_page(page);
829 }
830 if (pte)
831 pte_unmap(pte);
832 blk_finish_plug(&plug);
833 swap_read_unplug(splug);
834 lru_add_drain();
835 skip:
836 /* The page was likely read above, so no need for plugging here */
837 return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
838 NULL);
839 }
840
841 /**
842 * swapin_readahead - swap in pages in hope we need them soon
843 * @entry: swap entry of this memory
844 * @gfp_mask: memory allocation flags
845 * @vmf: fault information
846 *
847 * Returns the struct page for entry and addr, after queueing swapin.
848 *
849 * It's a main entry function for swap readahead. By the configuration,
850 * it will read ahead blocks by cluster-based(ie, physical disk based)
851 * or vma-based(ie, virtual address based on faulty address) readahead.
852 */
swapin_readahead(swp_entry_t entry,gfp_t gfp_mask,struct vm_fault * vmf)853 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
854 struct vm_fault *vmf)
855 {
856 return swap_use_vma_readahead() ?
857 swap_vma_readahead(entry, gfp_mask, vmf) :
858 swap_cluster_readahead(entry, gfp_mask, vmf);
859 }
860
861 #ifdef CONFIG_SYSFS
vma_ra_enabled_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)862 static ssize_t vma_ra_enabled_show(struct kobject *kobj,
863 struct kobj_attribute *attr, char *buf)
864 {
865 return sysfs_emit(buf, "%s\n",
866 enable_vma_readahead ? "true" : "false");
867 }
vma_ra_enabled_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)868 static ssize_t vma_ra_enabled_store(struct kobject *kobj,
869 struct kobj_attribute *attr,
870 const char *buf, size_t count)
871 {
872 ssize_t ret;
873
874 ret = kstrtobool(buf, &enable_vma_readahead);
875 if (ret)
876 return ret;
877
878 return count;
879 }
880 static struct kobj_attribute vma_ra_enabled_attr = __ATTR_RW(vma_ra_enabled);
881
882 static struct attribute *swap_attrs[] = {
883 &vma_ra_enabled_attr.attr,
884 NULL,
885 };
886
887 static const struct attribute_group swap_attr_group = {
888 .attrs = swap_attrs,
889 };
890
swap_init_sysfs(void)891 static int __init swap_init_sysfs(void)
892 {
893 int err;
894 struct kobject *swap_kobj;
895
896 swap_kobj = kobject_create_and_add("swap", mm_kobj);
897 if (!swap_kobj) {
898 pr_err("failed to create swap kobject\n");
899 return -ENOMEM;
900 }
901 err = sysfs_create_group(swap_kobj, &swap_attr_group);
902 if (err) {
903 pr_err("failed to register swap group\n");
904 goto delete_obj;
905 }
906 return 0;
907
908 delete_obj:
909 kobject_put(swap_kobj);
910 return err;
911 }
912 subsys_initcall(swap_init_sysfs);
913 #endif
914
