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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 
27 /*
28  * swapper_space is a fiction, retained to simplify the path through
29  * vmscan's shrink_page_list.
30  */
31 static const struct address_space_operations swap_aops = {
32 	.writepage	= swap_writepage,
33 	.set_page_dirty	= swap_set_page_dirty,
34 #ifdef CONFIG_MIGRATION
35 	.migratepage	= migrate_page,
36 #endif
37 };
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 #define INC_CACHE_INFO(x)	data_race(swap_cache_info.x++)
62 #define ADD_CACHE_INFO(x, nr)	data_race(swap_cache_info.x += (nr))
63 
64 static struct {
65 	unsigned long add_total;
66 	unsigned long del_total;
67 	unsigned long find_success;
68 	unsigned long find_total;
69 } swap_cache_info;
70 
71 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
72 
show_swap_cache_info(void)73 void show_swap_cache_info(void)
74 {
75 	printk("%lu pages in swap cache\n", total_swapcache_pages());
76 	printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
77 		swap_cache_info.add_total, swap_cache_info.del_total,
78 		swap_cache_info.find_success, swap_cache_info.find_total);
79 	printk("Free swap  = %ldkB\n",
80 		get_nr_swap_pages() << (PAGE_SHIFT - 10));
81 	printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
82 }
83 
get_shadow_from_swap_cache(swp_entry_t entry)84 void *get_shadow_from_swap_cache(swp_entry_t entry)
85 {
86 	struct address_space *address_space = swap_address_space(entry);
87 	pgoff_t idx = swp_offset(entry);
88 	struct page *page;
89 
90 	page = xa_load(&address_space->i_pages, idx);
91 	if (xa_is_value(page))
92 		return page;
93 	return NULL;
94 }
95 
96 /*
97  * add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
98  * but sets SwapCache flag and private instead of mapping and index.
99  */
add_to_swap_cache(struct page * page,swp_entry_t entry,gfp_t gfp,void ** shadowp)100 int add_to_swap_cache(struct page *page, swp_entry_t entry,
101 			gfp_t gfp, void **shadowp)
102 {
103 	struct address_space *address_space = swap_address_space(entry);
104 	pgoff_t idx = swp_offset(entry);
105 	XA_STATE_ORDER(xas, &address_space->i_pages, idx, compound_order(page));
106 	unsigned long i, nr = thp_nr_pages(page);
107 	void *old;
108 
109 	VM_BUG_ON_PAGE(!PageLocked(page), page);
110 	VM_BUG_ON_PAGE(PageSwapCache(page), page);
111 	VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
112 
113 	page_ref_add(page, nr);
114 	SetPageSwapCache(page);
115 
116 	do {
117 		xas_lock_irq(&xas);
118 		xas_create_range(&xas);
119 		if (xas_error(&xas))
120 			goto unlock;
121 		for (i = 0; i < nr; i++) {
122 			VM_BUG_ON_PAGE(xas.xa_index != idx + i, page);
123 			old = xas_load(&xas);
124 			if (xa_is_value(old)) {
125 				if (shadowp)
126 					*shadowp = old;
127 			}
128 			set_page_private(page + i, entry.val + i);
129 			xas_store(&xas, page);
130 			xas_next(&xas);
131 		}
132 		address_space->nrpages += nr;
133 		__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
134 		__mod_lruvec_page_state(page, NR_SWAPCACHE, nr);
135 		ADD_CACHE_INFO(add_total, nr);
136 unlock:
137 		xas_unlock_irq(&xas);
138 	} while (xas_nomem(&xas, gfp));
139 
140 	if (!xas_error(&xas))
141 		return 0;
142 
143 	ClearPageSwapCache(page);
144 	page_ref_sub(page, nr);
145 	return xas_error(&xas);
146 }
147 
148 /*
149  * This must be called only on pages that have
150  * been verified to be in the swap cache.
151  */
__delete_from_swap_cache(struct page * page,swp_entry_t entry,void * shadow)152 void __delete_from_swap_cache(struct page *page,
153 			swp_entry_t entry, void *shadow)
154 {
155 	struct address_space *address_space = swap_address_space(entry);
156 	int i, nr = thp_nr_pages(page);
157 	pgoff_t idx = swp_offset(entry);
158 	XA_STATE(xas, &address_space->i_pages, idx);
159 
160 	VM_BUG_ON_PAGE(!PageLocked(page), page);
161 	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
162 	VM_BUG_ON_PAGE(PageWriteback(page), page);
163 
164 	for (i = 0; i < nr; i++) {
165 		void *entry = xas_store(&xas, shadow);
166 		VM_BUG_ON_PAGE(entry != page, entry);
167 		set_page_private(page + i, 0);
168 		xas_next(&xas);
169 	}
170 	ClearPageSwapCache(page);
171 	address_space->nrpages -= nr;
172 	__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
173 	__mod_lruvec_page_state(page, NR_SWAPCACHE, -nr);
174 	ADD_CACHE_INFO(del_total, nr);
175 }
176 
177 /**
178  * add_to_swap - allocate swap space for a page
179  * @page: page we want to move to swap
180  *
181  * Allocate swap space for the page and add the page to the
182  * swap cache.  Caller needs to hold the page lock.
183  */
add_to_swap(struct page * page)184 int add_to_swap(struct page *page)
185 {
186 	swp_entry_t entry;
187 	int err;
188 
189 	VM_BUG_ON_PAGE(!PageLocked(page), page);
190 	VM_BUG_ON_PAGE(!PageUptodate(page), page);
191 
192 	entry = get_swap_page(page);
193 	if (!entry.val)
194 		return 0;
195 
196 	/*
197 	 * XArray node allocations from PF_MEMALLOC contexts could
198 	 * completely exhaust the page allocator. __GFP_NOMEMALLOC
199 	 * stops emergency reserves from being allocated.
200 	 *
201 	 * TODO: this could cause a theoretical memory reclaim
202 	 * deadlock in the swap out path.
203 	 */
204 	/*
205 	 * Add it to the swap cache.
206 	 */
207 	err = add_to_swap_cache(page, entry,
208 			__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN, NULL);
209 	if (err)
210 		/*
211 		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
212 		 * clear SWAP_HAS_CACHE flag.
213 		 */
214 		goto fail;
215 	/*
216 	 * Normally the page will be dirtied in unmap because its pte should be
217 	 * dirty. A special case is MADV_FREE page. The page's pte could have
218 	 * dirty bit cleared but the page's SwapBacked bit is still set because
219 	 * clearing the dirty bit and SwapBacked bit has no lock protected. For
220 	 * such page, unmap will not set dirty bit for it, so page reclaim will
221 	 * not write the page out. This can cause data corruption when the page
222 	 * is swap in later. Always setting the dirty bit for the page solves
223 	 * the problem.
224 	 */
225 	set_page_dirty(page);
226 
227 	return 1;
228 
229 fail:
230 	put_swap_page(page, entry);
231 	return 0;
232 }
233 
234 /*
235  * This must be called only on pages that have
236  * been verified to be in the swap cache and locked.
237  * It will never put the page into the free list,
238  * the caller has a reference on the page.
239  */
delete_from_swap_cache(struct page * page)240 void delete_from_swap_cache(struct page *page)
241 {
242 	swp_entry_t entry = { .val = page_private(page) };
243 	struct address_space *address_space = swap_address_space(entry);
244 
245 	xa_lock_irq(&address_space->i_pages);
246 	__delete_from_swap_cache(page, entry, NULL);
247 	xa_unlock_irq(&address_space->i_pages);
248 
249 	put_swap_page(page, entry);
250 	page_ref_sub(page, thp_nr_pages(page));
251 }
252 
clear_shadow_from_swap_cache(int type,unsigned long begin,unsigned long end)253 void clear_shadow_from_swap_cache(int type, unsigned long begin,
254 				unsigned long end)
255 {
256 	unsigned long curr = begin;
257 	void *old;
258 
259 	for (;;) {
260 		swp_entry_t entry = swp_entry(type, curr);
261 		struct address_space *address_space = swap_address_space(entry);
262 		XA_STATE(xas, &address_space->i_pages, curr);
263 
264 		xa_lock_irq(&address_space->i_pages);
265 		xas_for_each(&xas, old, end) {
266 			if (!xa_is_value(old))
267 				continue;
268 			xas_store(&xas, NULL);
269 		}
270 		xa_unlock_irq(&address_space->i_pages);
271 
272 		/* search the next swapcache until we meet end */
273 		curr >>= SWAP_ADDRESS_SPACE_SHIFT;
274 		curr++;
275 		curr <<= SWAP_ADDRESS_SPACE_SHIFT;
276 		if (curr > end)
277 			break;
278 	}
279 }
280 
281 /*
282  * If we are the only user, then try to free up the swap cache.
283  *
284  * Its ok to check for PageSwapCache without the page lock
285  * here because we are going to recheck again inside
286  * try_to_free_swap() _with_ the lock.
287  * 					- Marcelo
288  */
free_swap_cache(struct page * page)289 void free_swap_cache(struct page *page)
290 {
291 	if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
292 		try_to_free_swap(page);
293 		unlock_page(page);
294 	}
295 }
296 
297 /*
298  * Perform a free_page(), also freeing any swap cache associated with
299  * this page if it is the last user of the page.
300  */
free_page_and_swap_cache(struct page * page)301 void free_page_and_swap_cache(struct page *page)
302 {
303 	free_swap_cache(page);
304 	if (!is_huge_zero_page(page))
305 		put_page(page);
306 }
307 
308 /*
309  * Passed an array of pages, drop them all from swapcache and then release
310  * them.  They are removed from the LRU and freed if this is their last use.
311  */
free_pages_and_swap_cache(struct page ** pages,int nr)312 void free_pages_and_swap_cache(struct page **pages, int nr)
313 {
314 	struct page **pagep = pages;
315 	int i;
316 
317 	lru_add_drain();
318 	for (i = 0; i < nr; i++)
319 		free_swap_cache(pagep[i]);
320 	release_pages(pagep, nr);
321 }
322 
swap_use_vma_readahead(void)323 static inline bool swap_use_vma_readahead(void)
324 {
325 	return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
326 }
327 
328 /*
329  * Lookup a swap entry in the swap cache. A found page will be returned
330  * unlocked and with its refcount incremented - we rely on the kernel
331  * lock getting page table operations atomic even if we drop the page
332  * lock before returning.
333  */
lookup_swap_cache(swp_entry_t entry,struct vm_area_struct * vma,unsigned long addr)334 struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
335 			       unsigned long addr)
336 {
337 	struct page *page;
338 	struct swap_info_struct *si;
339 
340 	si = get_swap_device(entry);
341 	if (!si)
342 		return NULL;
343 	page = find_get_page(swap_address_space(entry), swp_offset(entry));
344 	put_swap_device(si);
345 
346 	INC_CACHE_INFO(find_total);
347 	if (page) {
348 		bool vma_ra = swap_use_vma_readahead();
349 		bool readahead;
350 
351 		INC_CACHE_INFO(find_success);
352 		/*
353 		 * At the moment, we don't support PG_readahead for anon THP
354 		 * so let's bail out rather than confusing the readahead stat.
355 		 */
356 		if (unlikely(PageTransCompound(page)))
357 			return page;
358 
359 		readahead = TestClearPageReadahead(page);
360 		if (vma && vma_ra) {
361 			unsigned long ra_val;
362 			int win, hits;
363 
364 			ra_val = GET_SWAP_RA_VAL(vma);
365 			win = SWAP_RA_WIN(ra_val);
366 			hits = SWAP_RA_HITS(ra_val);
367 			if (readahead)
368 				hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
369 			atomic_long_set(&vma->swap_readahead_info,
370 					SWAP_RA_VAL(addr, win, hits));
371 		}
372 
373 		if (readahead) {
374 			count_vm_event(SWAP_RA_HIT);
375 			if (!vma || !vma_ra)
376 				atomic_inc(&swapin_readahead_hits);
377 		}
378 	}
379 
380 	return page;
381 }
382 
383 /**
384  * find_get_incore_page - Find and get a page from the page or swap caches.
385  * @mapping: The address_space to search.
386  * @index: The page cache index.
387  *
388  * This differs from find_get_page() in that it will also look for the
389  * page in the swap cache.
390  *
391  * Return: The found page or %NULL.
392  */
find_get_incore_page(struct address_space * mapping,pgoff_t index)393 struct page *find_get_incore_page(struct address_space *mapping, pgoff_t index)
394 {
395 	swp_entry_t swp;
396 	struct swap_info_struct *si;
397 	struct page *page = pagecache_get_page(mapping, index,
398 						FGP_ENTRY | FGP_HEAD, 0);
399 
400 	if (!page)
401 		return page;
402 	if (!xa_is_value(page))
403 		return find_subpage(page, index);
404 	if (!shmem_mapping(mapping))
405 		return NULL;
406 
407 	swp = radix_to_swp_entry(page);
408 	/* Prevent swapoff from happening to us */
409 	si = get_swap_device(swp);
410 	if (!si)
411 		return NULL;
412 	page = find_get_page(swap_address_space(swp), swp_offset(swp));
413 	put_swap_device(si);
414 	return page;
415 }
416 
__read_swap_cache_async(swp_entry_t entry,gfp_t gfp_mask,struct vm_area_struct * vma,unsigned long addr,bool * new_page_allocated)417 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
418 			struct vm_area_struct *vma, unsigned long addr,
419 			bool *new_page_allocated)
420 {
421 	struct swap_info_struct *si;
422 	struct page *page;
423 	void *shadow = NULL;
424 
425 	*new_page_allocated = false;
426 
427 	for (;;) {
428 		int err;
429 		/*
430 		 * First check the swap cache.  Since this is normally
431 		 * called after lookup_swap_cache() failed, re-calling
432 		 * that would confuse statistics.
433 		 */
434 		si = get_swap_device(entry);
435 		if (!si)
436 			return NULL;
437 		page = find_get_page(swap_address_space(entry),
438 				     swp_offset(entry));
439 		put_swap_device(si);
440 		if (page)
441 			return page;
442 
443 		/*
444 		 * Just skip read ahead for unused swap slot.
445 		 * During swap_off when swap_slot_cache is disabled,
446 		 * we have to handle the race between putting
447 		 * swap entry in swap cache and marking swap slot
448 		 * as SWAP_HAS_CACHE.  That's done in later part of code or
449 		 * else swap_off will be aborted if we return NULL.
450 		 */
451 		if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
452 			return NULL;
453 
454 		/*
455 		 * Get a new page to read into from swap.  Allocate it now,
456 		 * before marking swap_map SWAP_HAS_CACHE, when -EEXIST will
457 		 * cause any racers to loop around until we add it to cache.
458 		 */
459 		page = alloc_page_vma(gfp_mask, vma, addr);
460 		if (!page)
461 			return NULL;
462 
463 		/*
464 		 * Swap entry may have been freed since our caller observed it.
465 		 */
466 		err = swapcache_prepare(entry);
467 		if (!err)
468 			break;
469 
470 		put_page(page);
471 		if (err != -EEXIST)
472 			return NULL;
473 
474 		/*
475 		 * We might race against __delete_from_swap_cache(), and
476 		 * stumble across a swap_map entry whose SWAP_HAS_CACHE
477 		 * has not yet been cleared.  Or race against another
478 		 * __read_swap_cache_async(), which has set SWAP_HAS_CACHE
479 		 * in swap_map, but not yet added its page to swap cache.
480 		 */
481 		schedule_timeout_uninterruptible(1);
482 	}
483 
484 	/*
485 	 * The swap entry is ours to swap in. Prepare the new page.
486 	 */
487 
488 	__SetPageLocked(page);
489 	__SetPageSwapBacked(page);
490 
491 	if (mem_cgroup_swapin_charge_page(page, NULL, gfp_mask, entry))
492 		goto fail_unlock;
493 
494 	/* May fail (-ENOMEM) if XArray node allocation failed. */
495 	if (add_to_swap_cache(page, entry, gfp_mask & GFP_RECLAIM_MASK, &shadow))
496 		goto fail_unlock;
497 
498 	mem_cgroup_swapin_uncharge_swap(entry);
499 
500 	if (shadow)
501 		workingset_refault(page, shadow);
502 
503 	/* Caller will initiate read into locked page */
504 	lru_cache_add(page);
505 	*new_page_allocated = true;
506 	return page;
507 
508 fail_unlock:
509 	put_swap_page(page, entry);
510 	unlock_page(page);
511 	put_page(page);
512 	return NULL;
513 }
514 
515 /*
516  * Locate a page of swap in physical memory, reserving swap cache space
517  * and reading the disk if it is not already cached.
518  * A failure return means that either the page allocation failed or that
519  * the swap entry is no longer in use.
520  */
read_swap_cache_async(swp_entry_t entry,gfp_t gfp_mask,struct vm_area_struct * vma,unsigned long addr,bool do_poll)521 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
522 		struct vm_area_struct *vma, unsigned long addr, bool do_poll)
523 {
524 	bool page_was_allocated;
525 	struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
526 			vma, addr, &page_was_allocated);
527 
528 	if (page_was_allocated)
529 		swap_readpage(retpage, do_poll);
530 
531 	return retpage;
532 }
533 
__swapin_nr_pages(unsigned long prev_offset,unsigned long offset,int hits,int max_pages,int prev_win)534 static unsigned int __swapin_nr_pages(unsigned long prev_offset,
535 				      unsigned long offset,
536 				      int hits,
537 				      int max_pages,
538 				      int prev_win)
539 {
540 	unsigned int pages, last_ra;
541 
542 	/*
543 	 * This heuristic has been found to work well on both sequential and
544 	 * random loads, swapping to hard disk or to SSD: please don't ask
545 	 * what the "+ 2" means, it just happens to work well, that's all.
546 	 */
547 	pages = hits + 2;
548 	if (pages == 2) {
549 		/*
550 		 * We can have no readahead hits to judge by: but must not get
551 		 * stuck here forever, so check for an adjacent offset instead
552 		 * (and don't even bother to check whether swap type is same).
553 		 */
554 		if (offset != prev_offset + 1 && offset != prev_offset - 1)
555 			pages = 1;
556 	} else {
557 		unsigned int roundup = 4;
558 		while (roundup < pages)
559 			roundup <<= 1;
560 		pages = roundup;
561 	}
562 
563 	if (pages > max_pages)
564 		pages = max_pages;
565 
566 	/* Don't shrink readahead too fast */
567 	last_ra = prev_win / 2;
568 	if (pages < last_ra)
569 		pages = last_ra;
570 
571 	return pages;
572 }
573 
swapin_nr_pages(unsigned long offset)574 static unsigned long swapin_nr_pages(unsigned long offset)
575 {
576 	static unsigned long prev_offset;
577 	unsigned int hits, pages, max_pages;
578 	static atomic_t last_readahead_pages;
579 
580 	max_pages = 1 << READ_ONCE(page_cluster);
581 	if (max_pages <= 1)
582 		return 1;
583 
584 	hits = atomic_xchg(&swapin_readahead_hits, 0);
585 	pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits,
586 				  max_pages,
587 				  atomic_read(&last_readahead_pages));
588 	if (!hits)
589 		WRITE_ONCE(prev_offset, offset);
590 	atomic_set(&last_readahead_pages, pages);
591 
592 	return pages;
593 }
594 
595 /**
596  * swap_cluster_readahead - swap in pages in hope we need them soon
597  * @entry: swap entry of this memory
598  * @gfp_mask: memory allocation flags
599  * @vmf: fault information
600  *
601  * Returns the struct page for entry and addr, after queueing swapin.
602  *
603  * Primitive swap readahead code. We simply read an aligned block of
604  * (1 << page_cluster) entries in the swap area. This method is chosen
605  * because it doesn't cost us any seek time.  We also make sure to queue
606  * the 'original' request together with the readahead ones...
607  *
608  * This has been extended to use the NUMA policies from the mm triggering
609  * the readahead.
610  *
611  * Caller must hold read mmap_lock if vmf->vma is not NULL.
612  */
swap_cluster_readahead(swp_entry_t entry,gfp_t gfp_mask,struct vm_fault * vmf)613 struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
614 				struct vm_fault *vmf)
615 {
616 	struct page *page;
617 	unsigned long entry_offset = swp_offset(entry);
618 	unsigned long offset = entry_offset;
619 	unsigned long start_offset, end_offset;
620 	unsigned long mask;
621 	struct swap_info_struct *si = swp_swap_info(entry);
622 	struct blk_plug plug;
623 	bool do_poll = true, page_allocated;
624 	struct vm_area_struct *vma = vmf->vma;
625 	unsigned long addr = vmf->address;
626 
627 	mask = swapin_nr_pages(offset) - 1;
628 	if (!mask)
629 		goto skip;
630 
631 	do_poll = false;
632 	/* Read a page_cluster sized and aligned cluster around offset. */
633 	start_offset = offset & ~mask;
634 	end_offset = offset | mask;
635 	if (!start_offset)	/* First page is swap header. */
636 		start_offset++;
637 	if (end_offset >= si->max)
638 		end_offset = si->max - 1;
639 
640 	blk_start_plug(&plug);
641 	for (offset = start_offset; offset <= end_offset ; offset++) {
642 		/* Ok, do the async read-ahead now */
643 		page = __read_swap_cache_async(
644 			swp_entry(swp_type(entry), offset),
645 			gfp_mask, vma, addr, &page_allocated);
646 		if (!page)
647 			continue;
648 		if (page_allocated) {
649 			swap_readpage(page, false);
650 			if (offset != entry_offset) {
651 				SetPageReadahead(page);
652 				count_vm_event(SWAP_RA);
653 			}
654 		}
655 		put_page(page);
656 	}
657 	blk_finish_plug(&plug);
658 
659 	lru_add_drain();	/* Push any new pages onto the LRU now */
660 skip:
661 	return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll);
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 vm_area_struct *vma = vmf->vma;
793 	struct page *page;
794 	pte_t *pte, pentry;
795 	swp_entry_t entry;
796 	unsigned int i;
797 	bool page_allocated;
798 	struct vma_swap_readahead ra_info = {
799 		.win = 1,
800 	};
801 
802 	swap_ra_info(vmf, &ra_info);
803 	if (ra_info.win == 1)
804 		goto skip;
805 
806 	blk_start_plug(&plug);
807 	for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
808 	     i++, pte++) {
809 		pentry = *pte;
810 		if (pte_none(pentry))
811 			continue;
812 		if (pte_present(pentry))
813 			continue;
814 		entry = pte_to_swp_entry(pentry);
815 		if (unlikely(non_swap_entry(entry)))
816 			continue;
817 		page = __read_swap_cache_async(entry, gfp_mask, vma,
818 					       vmf->address, &page_allocated);
819 		if (!page)
820 			continue;
821 		if (page_allocated) {
822 			swap_readpage(page, false);
823 			if (i != ra_info.offset) {
824 				SetPageReadahead(page);
825 				count_vm_event(SWAP_RA);
826 			}
827 		}
828 		put_page(page);
829 	}
830 	blk_finish_plug(&plug);
831 	lru_add_drain();
832 skip:
833 	return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
834 				     ra_info.win == 1);
835 }
836 
837 /**
838  * swapin_readahead - swap in pages in hope we need them soon
839  * @entry: swap entry of this memory
840  * @gfp_mask: memory allocation flags
841  * @vmf: fault information
842  *
843  * Returns the struct page for entry and addr, after queueing swapin.
844  *
845  * It's a main entry function for swap readahead. By the configuration,
846  * it will read ahead blocks by cluster-based(ie, physical disk based)
847  * or vma-based(ie, virtual address based on faulty address) readahead.
848  */
swapin_readahead(swp_entry_t entry,gfp_t gfp_mask,struct vm_fault * vmf)849 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
850 				struct vm_fault *vmf)
851 {
852 	return swap_use_vma_readahead() ?
853 			swap_vma_readahead(entry, gfp_mask, vmf) :
854 			swap_cluster_readahead(entry, gfp_mask, vmf);
855 }
856 
857 #ifdef CONFIG_SYSFS
vma_ra_enabled_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)858 static ssize_t vma_ra_enabled_show(struct kobject *kobj,
859 				     struct kobj_attribute *attr, char *buf)
860 {
861 	return sysfs_emit(buf, "%s\n",
862 			  enable_vma_readahead ? "true" : "false");
863 }
vma_ra_enabled_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)864 static ssize_t vma_ra_enabled_store(struct kobject *kobj,
865 				      struct kobj_attribute *attr,
866 				      const char *buf, size_t count)
867 {
868 	if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1))
869 		enable_vma_readahead = true;
870 	else if (!strncmp(buf, "false", 5) || !strncmp(buf, "0", 1))
871 		enable_vma_readahead = false;
872 	else
873 		return -EINVAL;
874 
875 	return count;
876 }
877 static struct kobj_attribute vma_ra_enabled_attr =
878 	__ATTR(vma_ra_enabled, 0644, vma_ra_enabled_show,
879 	       vma_ra_enabled_store);
880 
881 static struct attribute *swap_attrs[] = {
882 	&vma_ra_enabled_attr.attr,
883 	NULL,
884 };
885 
886 static const struct attribute_group swap_attr_group = {
887 	.attrs = swap_attrs,
888 };
889 
swap_init_sysfs(void)890 static int __init swap_init_sysfs(void)
891 {
892 	int err;
893 	struct kobject *swap_kobj;
894 
895 	swap_kobj = kobject_create_and_add("swap", mm_kobj);
896 	if (!swap_kobj) {
897 		pr_err("failed to create swap kobject\n");
898 		return -ENOMEM;
899 	}
900 	err = sysfs_create_group(swap_kobj, &swap_attr_group);
901 	if (err) {
902 		pr_err("failed to register swap group\n");
903 		goto delete_obj;
904 	}
905 	return 0;
906 
907 delete_obj:
908 	kobject_put(swap_kobj);
909 	return err;
910 }
911 subsys_initcall(swap_init_sysfs);
912 #endif
913