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