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 #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 */
32 static const struct address_space_operations swap_aops = {
33 .writepage = swap_writepage,
34 .dirty_folio = noop_dirty_folio,
35 #ifdef CONFIG_MIGRATION
36 .migratepage = migrate_page,
37 #endif
38 };
39
40 struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
41 static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
42 static 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
62 #define INC_CACHE_INFO(x) data_race(swap_cache_info.x++)
63 #define ADD_CACHE_INFO(x, nr) data_race(swap_cache_info.x += (nr))
64
65 static struct {
66 unsigned long add_total;
67 unsigned long del_total;
68 unsigned long find_success;
69 unsigned long find_total;
70 } swap_cache_info;
71
72 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
73
show_swap_cache_info(void)74 void show_swap_cache_info(void)
75 {
76 printk("%lu pages in swap cache\n", total_swapcache_pages());
77 printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
78 swap_cache_info.add_total, swap_cache_info.del_total,
79 swap_cache_info.find_success, swap_cache_info.find_total);
80 printk("Free swap = %ldkB\n",
81 get_nr_swap_pages() << (PAGE_SHIFT - 10));
82 printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
83 }
84
get_shadow_from_swap_cache(swp_entry_t entry)85 void *get_shadow_from_swap_cache(swp_entry_t entry)
86 {
87 struct address_space *address_space = swap_address_space(entry);
88 pgoff_t idx = swp_offset(entry);
89 struct page *page;
90
91 page = xa_load(&address_space->i_pages, idx);
92 if (xa_is_value(page))
93 return page;
94 return NULL;
95 }
96
97 /*
98 * add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
99 * but sets SwapCache flag and private instead of mapping and index.
100 */
add_to_swap_cache(struct page * page,swp_entry_t entry,gfp_t gfp,void ** shadowp)101 int add_to_swap_cache(struct page *page, swp_entry_t entry,
102 gfp_t gfp, void **shadowp)
103 {
104 struct address_space *address_space = swap_address_space(entry);
105 pgoff_t idx = swp_offset(entry);
106 XA_STATE_ORDER(xas, &address_space->i_pages, idx, compound_order(page));
107 unsigned long i, nr = thp_nr_pages(page);
108 void *old;
109
110 VM_BUG_ON_PAGE(!PageLocked(page), page);
111 VM_BUG_ON_PAGE(PageSwapCache(page), page);
112 VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
113
114 page_ref_add(page, nr);
115 SetPageSwapCache(page);
116
117 do {
118 xas_lock_irq(&xas);
119 xas_create_range(&xas);
120 if (xas_error(&xas))
121 goto unlock;
122 for (i = 0; i < nr; i++) {
123 VM_BUG_ON_PAGE(xas.xa_index != idx + i, page);
124 old = xas_load(&xas);
125 if (xa_is_value(old)) {
126 if (shadowp)
127 *shadowp = old;
128 }
129 set_page_private(page + i, entry.val + i);
130 xas_store(&xas, page);
131 xas_next(&xas);
132 }
133 address_space->nrpages += nr;
134 __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
135 __mod_lruvec_page_state(page, NR_SWAPCACHE, nr);
136 ADD_CACHE_INFO(add_total, nr);
137 unlock:
138 xas_unlock_irq(&xas);
139 } while (xas_nomem(&xas, gfp));
140
141 if (!xas_error(&xas))
142 return 0;
143
144 ClearPageSwapCache(page);
145 page_ref_sub(page, nr);
146 return xas_error(&xas);
147 }
148
149 /*
150 * This must be called only on pages that have
151 * been verified to be in the swap cache.
152 */
__delete_from_swap_cache(struct page * page,swp_entry_t entry,void * shadow)153 void __delete_from_swap_cache(struct page *page,
154 swp_entry_t entry, void *shadow)
155 {
156 struct address_space *address_space = swap_address_space(entry);
157 int i, nr = thp_nr_pages(page);
158 pgoff_t idx = swp_offset(entry);
159 XA_STATE(xas, &address_space->i_pages, idx);
160
161 VM_BUG_ON_PAGE(!PageLocked(page), page);
162 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
163 VM_BUG_ON_PAGE(PageWriteback(page), page);
164
165 for (i = 0; i < nr; i++) {
166 void *entry = xas_store(&xas, shadow);
167 VM_BUG_ON_PAGE(entry != page, entry);
168 set_page_private(page + i, 0);
169 xas_next(&xas);
170 }
171 ClearPageSwapCache(page);
172 address_space->nrpages -= nr;
173 __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
174 __mod_lruvec_page_state(page, NR_SWAPCACHE, -nr);
175 ADD_CACHE_INFO(del_total, nr);
176 }
177
178 /**
179 * add_to_swap - allocate swap space for a folio
180 * @folio: folio we want to move to swap
181 *
182 * Allocate swap space for the folio and add the folio to the
183 * swap cache.
184 *
185 * Context: Caller needs to hold the folio lock.
186 * Return: Whether the folio was added to the swap cache.
187 */
add_to_swap(struct folio * folio)188 bool add_to_swap(struct folio *folio)
189 {
190 swp_entry_t entry;
191 int err;
192
193 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
194 VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);
195
196 entry = folio_alloc_swap(folio);
197 if (!entry.val)
198 return false;
199
200 /*
201 * XArray node allocations from PF_MEMALLOC contexts could
202 * completely exhaust the page allocator. __GFP_NOMEMALLOC
203 * stops emergency reserves from being allocated.
204 *
205 * TODO: this could cause a theoretical memory reclaim
206 * deadlock in the swap out path.
207 */
208 /*
209 * Add it to the swap cache.
210 */
211 err = add_to_swap_cache(&folio->page, entry,
212 __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN, NULL);
213 if (err)
214 /*
215 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
216 * clear SWAP_HAS_CACHE flag.
217 */
218 goto fail;
219 /*
220 * Normally the folio will be dirtied in unmap because its
221 * pte should be dirty. A special case is MADV_FREE page. The
222 * page's pte could have dirty bit cleared but the folio's
223 * SwapBacked flag is still set because clearing the dirty bit
224 * and SwapBacked flag has no lock protected. For such folio,
225 * unmap will not set dirty bit for it, so folio reclaim will
226 * not write the folio out. This can cause data corruption when
227 * the folio is swapped in later. Always setting the dirty flag
228 * for the folio solves the problem.
229 */
230 folio_mark_dirty(folio);
231
232 return true;
233
234 fail:
235 put_swap_page(&folio->page, entry);
236 return false;
237 }
238
239 /*
240 * This must be called only on pages that have
241 * been verified to be in the swap cache and locked.
242 * It will never put the page into the free list,
243 * the caller has a reference on the page.
244 */
delete_from_swap_cache(struct page * page)245 void delete_from_swap_cache(struct page *page)
246 {
247 swp_entry_t entry = { .val = page_private(page) };
248 struct address_space *address_space = swap_address_space(entry);
249
250 xa_lock_irq(&address_space->i_pages);
251 __delete_from_swap_cache(page, entry, NULL);
252 xa_unlock_irq(&address_space->i_pages);
253
254 put_swap_page(page, entry);
255 page_ref_sub(page, thp_nr_pages(page));
256 }
257
clear_shadow_from_swap_cache(int type,unsigned long begin,unsigned long end)258 void clear_shadow_from_swap_cache(int type, unsigned long begin,
259 unsigned long end)
260 {
261 unsigned long curr = begin;
262 void *old;
263
264 for (;;) {
265 swp_entry_t entry = swp_entry(type, curr);
266 struct address_space *address_space = swap_address_space(entry);
267 XA_STATE(xas, &address_space->i_pages, curr);
268
269 xa_lock_irq(&address_space->i_pages);
270 xas_for_each(&xas, old, end) {
271 if (!xa_is_value(old))
272 continue;
273 xas_store(&xas, NULL);
274 }
275 xa_unlock_irq(&address_space->i_pages);
276
277 /* search the next swapcache until we meet end */
278 curr >>= SWAP_ADDRESS_SPACE_SHIFT;
279 curr++;
280 curr <<= SWAP_ADDRESS_SPACE_SHIFT;
281 if (curr > end)
282 break;
283 }
284 }
285
286 /*
287 * If we are the only user, then try to free up the swap cache.
288 *
289 * Its ok to check for PageSwapCache without the page lock
290 * here because we are going to recheck again inside
291 * try_to_free_swap() _with_ the lock.
292 * - Marcelo
293 */
free_swap_cache(struct page * page)294 void free_swap_cache(struct page *page)
295 {
296 if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
297 try_to_free_swap(page);
298 unlock_page(page);
299 }
300 }
301
302 /*
303 * Perform a free_page(), also freeing any swap cache associated with
304 * this page if it is the last user of the page.
305 */
free_page_and_swap_cache(struct page * page)306 void free_page_and_swap_cache(struct page *page)
307 {
308 free_swap_cache(page);
309 if (!is_huge_zero_page(page))
310 put_page(page);
311 }
312
313 /*
314 * Passed an array of pages, drop them all from swapcache and then release
315 * them. They are removed from the LRU and freed if this is their last use.
316 */
free_pages_and_swap_cache(struct page ** pages,int nr)317 void free_pages_and_swap_cache(struct page **pages, int nr)
318 {
319 struct page **pagep = pages;
320 int i;
321
322 lru_add_drain();
323 for (i = 0; i < nr; i++)
324 free_swap_cache(pagep[i]);
325 release_pages(pagep, nr);
326 }
327
swap_use_vma_readahead(void)328 static inline bool swap_use_vma_readahead(void)
329 {
330 return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
331 }
332
333 /*
334 * Lookup a swap entry in the swap cache. A found page will be returned
335 * unlocked and with its refcount incremented - we rely on the kernel
336 * lock getting page table operations atomic even if we drop the page
337 * lock before returning.
338 */
lookup_swap_cache(swp_entry_t entry,struct vm_area_struct * vma,unsigned long addr)339 struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
340 unsigned long addr)
341 {
342 struct page *page;
343 struct swap_info_struct *si;
344
345 si = get_swap_device(entry);
346 if (!si)
347 return NULL;
348 page = find_get_page(swap_address_space(entry), swp_offset(entry));
349 put_swap_device(si);
350
351 INC_CACHE_INFO(find_total);
352 if (page) {
353 bool vma_ra = swap_use_vma_readahead();
354 bool readahead;
355
356 INC_CACHE_INFO(find_success);
357 /*
358 * At the moment, we don't support PG_readahead for anon THP
359 * so let's bail out rather than confusing the readahead stat.
360 */
361 if (unlikely(PageTransCompound(page)))
362 return page;
363
364 readahead = TestClearPageReadahead(page);
365 if (vma && vma_ra) {
366 unsigned long ra_val;
367 int win, hits;
368
369 ra_val = GET_SWAP_RA_VAL(vma);
370 win = SWAP_RA_WIN(ra_val);
371 hits = SWAP_RA_HITS(ra_val);
372 if (readahead)
373 hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
374 atomic_long_set(&vma->swap_readahead_info,
375 SWAP_RA_VAL(addr, win, hits));
376 }
377
378 if (readahead) {
379 count_vm_event(SWAP_RA_HIT);
380 if (!vma || !vma_ra)
381 atomic_inc(&swapin_readahead_hits);
382 }
383 }
384
385 return page;
386 }
387
388 /**
389 * find_get_incore_page - Find and get a page from the page or swap caches.
390 * @mapping: The address_space to search.
391 * @index: The page cache index.
392 *
393 * This differs from find_get_page() in that it will also look for the
394 * page in the swap cache.
395 *
396 * Return: The found page or %NULL.
397 */
find_get_incore_page(struct address_space * mapping,pgoff_t index)398 struct page *find_get_incore_page(struct address_space *mapping, pgoff_t index)
399 {
400 swp_entry_t swp;
401 struct swap_info_struct *si;
402 struct page *page = pagecache_get_page(mapping, index,
403 FGP_ENTRY | FGP_HEAD, 0);
404
405 if (!page)
406 return page;
407 if (!xa_is_value(page))
408 return find_subpage(page, index);
409 if (!shmem_mapping(mapping))
410 return NULL;
411
412 swp = radix_to_swp_entry(page);
413 /* There might be swapin error entries in shmem mapping. */
414 if (non_swap_entry(swp))
415 return NULL;
416 /* Prevent swapoff from happening to us */
417 si = get_swap_device(swp);
418 if (!si)
419 return NULL;
420 page = find_get_page(swap_address_space(swp), swp_offset(swp));
421 put_swap_device(si);
422 return page;
423 }
424
__read_swap_cache_async(swp_entry_t entry,gfp_t gfp_mask,struct vm_area_struct * vma,unsigned long addr,bool * new_page_allocated)425 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
426 struct vm_area_struct *vma, unsigned long addr,
427 bool *new_page_allocated)
428 {
429 struct swap_info_struct *si;
430 struct page *page;
431 void *shadow = NULL;
432
433 *new_page_allocated = false;
434
435 for (;;) {
436 int err;
437 /*
438 * First check the swap cache. Since this is normally
439 * called after lookup_swap_cache() failed, re-calling
440 * that would confuse statistics.
441 */
442 si = get_swap_device(entry);
443 if (!si)
444 return NULL;
445 page = find_get_page(swap_address_space(entry),
446 swp_offset(entry));
447 put_swap_device(si);
448 if (page)
449 return page;
450
451 /*
452 * Just skip read ahead for unused swap slot.
453 * During swap_off when swap_slot_cache is disabled,
454 * we have to handle the race between putting
455 * swap entry in swap cache and marking swap slot
456 * as SWAP_HAS_CACHE. That's done in later part of code or
457 * else swap_off will be aborted if we return NULL.
458 */
459 if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
460 return NULL;
461
462 /*
463 * Get a new page to read into from swap. Allocate it now,
464 * before marking swap_map SWAP_HAS_CACHE, when -EEXIST will
465 * cause any racers to loop around until we add it to cache.
466 */
467 page = alloc_page_vma(gfp_mask, vma, addr);
468 if (!page)
469 return NULL;
470
471 /*
472 * Swap entry may have been freed since our caller observed it.
473 */
474 err = swapcache_prepare(entry);
475 if (!err)
476 break;
477
478 put_page(page);
479 if (err != -EEXIST)
480 return NULL;
481
482 /*
483 * We might race against __delete_from_swap_cache(), and
484 * stumble across a swap_map entry whose SWAP_HAS_CACHE
485 * has not yet been cleared. Or race against another
486 * __read_swap_cache_async(), which has set SWAP_HAS_CACHE
487 * in swap_map, but not yet added its page to swap cache.
488 */
489 schedule_timeout_uninterruptible(1);
490 }
491
492 /*
493 * The swap entry is ours to swap in. Prepare the new page.
494 */
495
496 __SetPageLocked(page);
497 __SetPageSwapBacked(page);
498
499 if (mem_cgroup_swapin_charge_page(page, NULL, gfp_mask, entry))
500 goto fail_unlock;
501
502 /* May fail (-ENOMEM) if XArray node allocation failed. */
503 if (add_to_swap_cache(page, entry, gfp_mask & GFP_RECLAIM_MASK, &shadow))
504 goto fail_unlock;
505
506 mem_cgroup_swapin_uncharge_swap(entry);
507
508 if (shadow)
509 workingset_refault(page_folio(page), shadow);
510
511 /* Caller will initiate read into locked page */
512 lru_cache_add(page);
513 *new_page_allocated = true;
514 return page;
515
516 fail_unlock:
517 put_swap_page(page, entry);
518 unlock_page(page);
519 put_page(page);
520 return NULL;
521 }
522
523 /*
524 * Locate a page of swap in physical memory, reserving swap cache space
525 * and reading the disk if it is not already cached.
526 * A failure return means that either the page allocation failed or that
527 * the swap entry is no longer in use.
528 */
read_swap_cache_async(swp_entry_t entry,gfp_t gfp_mask,struct vm_area_struct * vma,unsigned long addr,bool do_poll,struct swap_iocb ** plug)529 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
530 struct vm_area_struct *vma,
531 unsigned long addr, bool do_poll,
532 struct swap_iocb **plug)
533 {
534 bool page_was_allocated;
535 struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
536 vma, addr, &page_was_allocated);
537
538 if (page_was_allocated)
539 swap_readpage(retpage, do_poll, plug);
540
541 return retpage;
542 }
543
__swapin_nr_pages(unsigned long prev_offset,unsigned long offset,int hits,int max_pages,int prev_win)544 static unsigned int __swapin_nr_pages(unsigned long prev_offset,
545 unsigned long offset,
546 int hits,
547 int max_pages,
548 int prev_win)
549 {
550 unsigned int pages, last_ra;
551
552 /*
553 * This heuristic has been found to work well on both sequential and
554 * random loads, swapping to hard disk or to SSD: please don't ask
555 * what the "+ 2" means, it just happens to work well, that's all.
556 */
557 pages = hits + 2;
558 if (pages == 2) {
559 /*
560 * We can have no readahead hits to judge by: but must not get
561 * stuck here forever, so check for an adjacent offset instead
562 * (and don't even bother to check whether swap type is same).
563 */
564 if (offset != prev_offset + 1 && offset != prev_offset - 1)
565 pages = 1;
566 } else {
567 unsigned int roundup = 4;
568 while (roundup < pages)
569 roundup <<= 1;
570 pages = roundup;
571 }
572
573 if (pages > max_pages)
574 pages = max_pages;
575
576 /* Don't shrink readahead too fast */
577 last_ra = prev_win / 2;
578 if (pages < last_ra)
579 pages = last_ra;
580
581 return pages;
582 }
583
swapin_nr_pages(unsigned long offset)584 static unsigned long swapin_nr_pages(unsigned long offset)
585 {
586 static unsigned long prev_offset;
587 unsigned int hits, pages, max_pages;
588 static atomic_t last_readahead_pages;
589
590 max_pages = 1 << READ_ONCE(page_cluster);
591 if (max_pages <= 1)
592 return 1;
593
594 hits = atomic_xchg(&swapin_readahead_hits, 0);
595 pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits,
596 max_pages,
597 atomic_read(&last_readahead_pages));
598 if (!hits)
599 WRITE_ONCE(prev_offset, offset);
600 atomic_set(&last_readahead_pages, pages);
601
602 return pages;
603 }
604
605 /**
606 * swap_cluster_readahead - swap in pages in hope we need them soon
607 * @entry: swap entry of this memory
608 * @gfp_mask: memory allocation flags
609 * @vmf: fault information
610 *
611 * Returns the struct page for entry and addr, after queueing swapin.
612 *
613 * Primitive swap readahead code. We simply read an aligned block of
614 * (1 << page_cluster) entries in the swap area. This method is chosen
615 * because it doesn't cost us any seek time. We also make sure to queue
616 * the 'original' request together with the readahead ones...
617 *
618 * This has been extended to use the NUMA policies from the mm triggering
619 * the readahead.
620 *
621 * Caller must hold read mmap_lock if vmf->vma is not NULL.
622 */
swap_cluster_readahead(swp_entry_t entry,gfp_t gfp_mask,struct vm_fault * vmf)623 struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
624 struct vm_fault *vmf)
625 {
626 struct page *page;
627 unsigned long entry_offset = swp_offset(entry);
628 unsigned long offset = entry_offset;
629 unsigned long start_offset, end_offset;
630 unsigned long mask;
631 struct swap_info_struct *si = swp_swap_info(entry);
632 struct blk_plug plug;
633 struct swap_iocb *splug = NULL;
634 bool do_poll = true, page_allocated;
635 struct vm_area_struct *vma = vmf->vma;
636 unsigned long addr = vmf->address;
637
638 mask = swapin_nr_pages(offset) - 1;
639 if (!mask)
640 goto skip;
641
642 do_poll = false;
643 /* Read a page_cluster sized and aligned cluster around offset. */
644 start_offset = offset & ~mask;
645 end_offset = offset | mask;
646 if (!start_offset) /* First page is swap header. */
647 start_offset++;
648 if (end_offset >= si->max)
649 end_offset = si->max - 1;
650
651 blk_start_plug(&plug);
652 for (offset = start_offset; offset <= end_offset ; offset++) {
653 /* Ok, do the async read-ahead now */
654 page = __read_swap_cache_async(
655 swp_entry(swp_type(entry), offset),
656 gfp_mask, vma, addr, &page_allocated);
657 if (!page)
658 continue;
659 if (page_allocated) {
660 swap_readpage(page, false, &splug);
661 if (offset != entry_offset) {
662 SetPageReadahead(page);
663 count_vm_event(SWAP_RA);
664 }
665 }
666 put_page(page);
667 }
668 blk_finish_plug(&plug);
669 swap_read_unplug(splug);
670
671 lru_add_drain(); /* Push any new pages onto the LRU now */
672 skip:
673 /* The page was likely read above, so no need for plugging here */
674 return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll, NULL);
675 }
676
init_swap_address_space(unsigned int type,unsigned long nr_pages)677 int init_swap_address_space(unsigned int type, unsigned long nr_pages)
678 {
679 struct address_space *spaces, *space;
680 unsigned int i, nr;
681
682 nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
683 spaces = kvcalloc(nr, sizeof(struct address_space), GFP_KERNEL);
684 if (!spaces)
685 return -ENOMEM;
686 for (i = 0; i < nr; i++) {
687 space = spaces + i;
688 xa_init_flags(&space->i_pages, XA_FLAGS_LOCK_IRQ);
689 atomic_set(&space->i_mmap_writable, 0);
690 space->a_ops = &swap_aops;
691 /* swap cache doesn't use writeback related tags */
692 mapping_set_no_writeback_tags(space);
693 }
694 nr_swapper_spaces[type] = nr;
695 swapper_spaces[type] = spaces;
696
697 return 0;
698 }
699
exit_swap_address_space(unsigned int type)700 void exit_swap_address_space(unsigned int type)
701 {
702 int i;
703 struct address_space *spaces = swapper_spaces[type];
704
705 for (i = 0; i < nr_swapper_spaces[type]; i++)
706 VM_WARN_ON_ONCE(!mapping_empty(&spaces[i]));
707 kvfree(spaces);
708 nr_swapper_spaces[type] = 0;
709 swapper_spaces[type] = NULL;
710 }
711
swap_ra_clamp_pfn(struct vm_area_struct * vma,unsigned long faddr,unsigned long lpfn,unsigned long rpfn,unsigned long * start,unsigned long * end)712 static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,
713 unsigned long faddr,
714 unsigned long lpfn,
715 unsigned long rpfn,
716 unsigned long *start,
717 unsigned long *end)
718 {
719 *start = max3(lpfn, PFN_DOWN(vma->vm_start),
720 PFN_DOWN(faddr & PMD_MASK));
721 *end = min3(rpfn, PFN_DOWN(vma->vm_end),
722 PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
723 }
724
swap_ra_info(struct vm_fault * vmf,struct vma_swap_readahead * ra_info)725 static void swap_ra_info(struct vm_fault *vmf,
726 struct vma_swap_readahead *ra_info)
727 {
728 struct vm_area_struct *vma = vmf->vma;
729 unsigned long ra_val;
730 unsigned long faddr, pfn, fpfn;
731 unsigned long start, end;
732 pte_t *pte, *orig_pte;
733 unsigned int max_win, hits, prev_win, win, left;
734 #ifndef CONFIG_64BIT
735 pte_t *tpte;
736 #endif
737
738 max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
739 SWAP_RA_ORDER_CEILING);
740 if (max_win == 1) {
741 ra_info->win = 1;
742 return;
743 }
744
745 faddr = vmf->address;
746 orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
747
748 fpfn = PFN_DOWN(faddr);
749 ra_val = GET_SWAP_RA_VAL(vma);
750 pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
751 prev_win = SWAP_RA_WIN(ra_val);
752 hits = SWAP_RA_HITS(ra_val);
753 ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits,
754 max_win, prev_win);
755 atomic_long_set(&vma->swap_readahead_info,
756 SWAP_RA_VAL(faddr, win, 0));
757
758 if (win == 1) {
759 pte_unmap(orig_pte);
760 return;
761 }
762
763 /* Copy the PTEs because the page table may be unmapped */
764 if (fpfn == pfn + 1)
765 swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
766 else if (pfn == fpfn + 1)
767 swap_ra_clamp_pfn(vma, faddr, fpfn - win + 1, fpfn + 1,
768 &start, &end);
769 else {
770 left = (win - 1) / 2;
771 swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
772 &start, &end);
773 }
774 ra_info->nr_pte = end - start;
775 ra_info->offset = fpfn - start;
776 pte -= ra_info->offset;
777 #ifdef CONFIG_64BIT
778 ra_info->ptes = pte;
779 #else
780 tpte = ra_info->ptes;
781 for (pfn = start; pfn != end; pfn++)
782 *tpte++ = *pte++;
783 #endif
784 pte_unmap(orig_pte);
785 }
786
787 /**
788 * swap_vma_readahead - swap in pages in hope we need them soon
789 * @fentry: swap entry of this memory
790 * @gfp_mask: memory allocation flags
791 * @vmf: fault information
792 *
793 * Returns the struct page for entry and addr, after queueing swapin.
794 *
795 * Primitive swap readahead code. We simply read in a few pages whose
796 * virtual addresses are around the fault address in the same vma.
797 *
798 * Caller must hold read mmap_lock if vmf->vma is not NULL.
799 *
800 */
swap_vma_readahead(swp_entry_t fentry,gfp_t gfp_mask,struct vm_fault * vmf)801 static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask,
802 struct vm_fault *vmf)
803 {
804 struct blk_plug plug;
805 struct swap_iocb *splug = NULL;
806 struct vm_area_struct *vma = vmf->vma;
807 struct page *page;
808 pte_t *pte, pentry;
809 swp_entry_t entry;
810 unsigned int i;
811 bool page_allocated;
812 struct vma_swap_readahead ra_info = {
813 .win = 1,
814 };
815
816 swap_ra_info(vmf, &ra_info);
817 if (ra_info.win == 1)
818 goto skip;
819
820 blk_start_plug(&plug);
821 for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
822 i++, pte++) {
823 pentry = *pte;
824 if (!is_swap_pte(pentry))
825 continue;
826 entry = pte_to_swp_entry(pentry);
827 if (unlikely(non_swap_entry(entry)))
828 continue;
829 page = __read_swap_cache_async(entry, gfp_mask, vma,
830 vmf->address, &page_allocated);
831 if (!page)
832 continue;
833 if (page_allocated) {
834 swap_readpage(page, false, &splug);
835 if (i != ra_info.offset) {
836 SetPageReadahead(page);
837 count_vm_event(SWAP_RA);
838 }
839 }
840 put_page(page);
841 }
842 blk_finish_plug(&plug);
843 swap_read_unplug(splug);
844 lru_add_drain();
845 skip:
846 /* The page was likely read above, so no need for plugging here */
847 return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
848 ra_info.win == 1, NULL);
849 }
850
851 /**
852 * swapin_readahead - swap in pages in hope we need them soon
853 * @entry: swap entry of this memory
854 * @gfp_mask: memory allocation flags
855 * @vmf: fault information
856 *
857 * Returns the struct page for entry and addr, after queueing swapin.
858 *
859 * It's a main entry function for swap readahead. By the configuration,
860 * it will read ahead blocks by cluster-based(ie, physical disk based)
861 * or vma-based(ie, virtual address based on faulty address) readahead.
862 */
swapin_readahead(swp_entry_t entry,gfp_t gfp_mask,struct vm_fault * vmf)863 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
864 struct vm_fault *vmf)
865 {
866 return swap_use_vma_readahead() ?
867 swap_vma_readahead(entry, gfp_mask, vmf) :
868 swap_cluster_readahead(entry, gfp_mask, vmf);
869 }
870
871 #ifdef CONFIG_SYSFS
vma_ra_enabled_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)872 static ssize_t vma_ra_enabled_show(struct kobject *kobj,
873 struct kobj_attribute *attr, char *buf)
874 {
875 return sysfs_emit(buf, "%s\n",
876 enable_vma_readahead ? "true" : "false");
877 }
vma_ra_enabled_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)878 static ssize_t vma_ra_enabled_store(struct kobject *kobj,
879 struct kobj_attribute *attr,
880 const char *buf, size_t count)
881 {
882 ssize_t ret;
883
884 ret = kstrtobool(buf, &enable_vma_readahead);
885 if (ret)
886 return ret;
887
888 return count;
889 }
890 static struct kobj_attribute vma_ra_enabled_attr = __ATTR_RW(vma_ra_enabled);
891
892 static struct attribute *swap_attrs[] = {
893 &vma_ra_enabled_attr.attr,
894 NULL,
895 };
896
897 static const struct attribute_group swap_attr_group = {
898 .attrs = swap_attrs,
899 };
900
swap_init_sysfs(void)901 static int __init swap_init_sysfs(void)
902 {
903 int err;
904 struct kobject *swap_kobj;
905
906 swap_kobj = kobject_create_and_add("swap", mm_kobj);
907 if (!swap_kobj) {
908 pr_err("failed to create swap kobject\n");
909 return -ENOMEM;
910 }
911 err = sysfs_create_group(swap_kobj, &swap_attr_group);
912 if (err) {
913 pr_err("failed to register swap group\n");
914 goto delete_obj;
915 }
916 return 0;
917
918 delete_obj:
919 kobject_put(swap_kobj);
920 return err;
921 }
922 subsys_initcall(swap_init_sysfs);
923 #endif
924