Loading...
1/*
2 * linux/mm/swap_state.c
3 *
4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
5 * Swap reorganised 29.12.95, Stephen Tweedie
6 *
7 * Rewritten to use page cache, (C) 1998 Stephen Tweedie
8 */
9#include <linux/mm.h>
10#include <linux/gfp.h>
11#include <linux/kernel_stat.h>
12#include <linux/swap.h>
13#include <linux/swapops.h>
14#include <linux/init.h>
15#include <linux/pagemap.h>
16#include <linux/backing-dev.h>
17#include <linux/blkdev.h>
18#include <linux/pagevec.h>
19#include <linux/migrate.h>
20#include <linux/page_cgroup.h>
21
22#include <asm/pgtable.h>
23
24/*
25 * swapper_space is a fiction, retained to simplify the path through
26 * vmscan's shrink_page_list.
27 */
28static const struct address_space_operations swap_aops = {
29 .writepage = swap_writepage,
30 .set_page_dirty = swap_set_page_dirty,
31 .migratepage = migrate_page,
32};
33
34static struct backing_dev_info swap_backing_dev_info = {
35 .name = "swap",
36 .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
37};
38
39struct address_space swapper_spaces[MAX_SWAPFILES] = {
40 [0 ... MAX_SWAPFILES - 1] = {
41 .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
42 .a_ops = &swap_aops,
43 .backing_dev_info = &swap_backing_dev_info,
44 }
45};
46
47#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
48
49static struct {
50 unsigned long add_total;
51 unsigned long del_total;
52 unsigned long find_success;
53 unsigned long find_total;
54} swap_cache_info;
55
56unsigned long total_swapcache_pages(void)
57{
58 int i;
59 unsigned long ret = 0;
60
61 for (i = 0; i < MAX_SWAPFILES; i++)
62 ret += swapper_spaces[i].nrpages;
63 return ret;
64}
65
66static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
67
68void show_swap_cache_info(void)
69{
70 printk("%lu pages in swap cache\n", total_swapcache_pages());
71 printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
72 swap_cache_info.add_total, swap_cache_info.del_total,
73 swap_cache_info.find_success, swap_cache_info.find_total);
74 printk("Free swap = %ldkB\n",
75 get_nr_swap_pages() << (PAGE_SHIFT - 10));
76 printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
77}
78
79/*
80 * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
81 * but sets SwapCache flag and private instead of mapping and index.
82 */
83int __add_to_swap_cache(struct page *page, swp_entry_t entry)
84{
85 int error;
86 struct address_space *address_space;
87
88 VM_BUG_ON_PAGE(!PageLocked(page), page);
89 VM_BUG_ON_PAGE(PageSwapCache(page), page);
90 VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
91
92 page_cache_get(page);
93 SetPageSwapCache(page);
94 set_page_private(page, entry.val);
95
96 address_space = swap_address_space(entry);
97 spin_lock_irq(&address_space->tree_lock);
98 error = radix_tree_insert(&address_space->page_tree,
99 entry.val, page);
100 if (likely(!error)) {
101 address_space->nrpages++;
102 __inc_zone_page_state(page, NR_FILE_PAGES);
103 INC_CACHE_INFO(add_total);
104 }
105 spin_unlock_irq(&address_space->tree_lock);
106
107 if (unlikely(error)) {
108 /*
109 * Only the context which have set SWAP_HAS_CACHE flag
110 * would call add_to_swap_cache().
111 * So add_to_swap_cache() doesn't returns -EEXIST.
112 */
113 VM_BUG_ON(error == -EEXIST);
114 set_page_private(page, 0UL);
115 ClearPageSwapCache(page);
116 page_cache_release(page);
117 }
118
119 return error;
120}
121
122
123int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
124{
125 int error;
126
127 error = radix_tree_maybe_preload(gfp_mask);
128 if (!error) {
129 error = __add_to_swap_cache(page, entry);
130 radix_tree_preload_end();
131 }
132 return error;
133}
134
135/*
136 * This must be called only on pages that have
137 * been verified to be in the swap cache.
138 */
139void __delete_from_swap_cache(struct page *page)
140{
141 swp_entry_t entry;
142 struct address_space *address_space;
143
144 VM_BUG_ON_PAGE(!PageLocked(page), page);
145 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
146 VM_BUG_ON_PAGE(PageWriteback(page), page);
147
148 entry.val = page_private(page);
149 address_space = swap_address_space(entry);
150 radix_tree_delete(&address_space->page_tree, page_private(page));
151 set_page_private(page, 0);
152 ClearPageSwapCache(page);
153 address_space->nrpages--;
154 __dec_zone_page_state(page, NR_FILE_PAGES);
155 INC_CACHE_INFO(del_total);
156}
157
158/**
159 * add_to_swap - allocate swap space for a page
160 * @page: page we want to move to swap
161 *
162 * Allocate swap space for the page and add the page to the
163 * swap cache. Caller needs to hold the page lock.
164 */
165int add_to_swap(struct page *page, struct list_head *list)
166{
167 swp_entry_t entry;
168 int err;
169
170 VM_BUG_ON_PAGE(!PageLocked(page), page);
171 VM_BUG_ON_PAGE(!PageUptodate(page), page);
172
173 entry = get_swap_page();
174 if (!entry.val)
175 return 0;
176
177 if (unlikely(PageTransHuge(page)))
178 if (unlikely(split_huge_page_to_list(page, list))) {
179 swapcache_free(entry, NULL);
180 return 0;
181 }
182
183 /*
184 * Radix-tree node allocations from PF_MEMALLOC contexts could
185 * completely exhaust the page allocator. __GFP_NOMEMALLOC
186 * stops emergency reserves from being allocated.
187 *
188 * TODO: this could cause a theoretical memory reclaim
189 * deadlock in the swap out path.
190 */
191 /*
192 * Add it to the swap cache and mark it dirty
193 */
194 err = add_to_swap_cache(page, entry,
195 __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
196
197 if (!err) { /* Success */
198 SetPageDirty(page);
199 return 1;
200 } else { /* -ENOMEM radix-tree allocation failure */
201 /*
202 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
203 * clear SWAP_HAS_CACHE flag.
204 */
205 swapcache_free(entry, NULL);
206 return 0;
207 }
208}
209
210/*
211 * This must be called only on pages that have
212 * been verified to be in the swap cache and locked.
213 * It will never put the page into the free list,
214 * the caller has a reference on the page.
215 */
216void delete_from_swap_cache(struct page *page)
217{
218 swp_entry_t entry;
219 struct address_space *address_space;
220
221 entry.val = page_private(page);
222
223 address_space = swap_address_space(entry);
224 spin_lock_irq(&address_space->tree_lock);
225 __delete_from_swap_cache(page);
226 spin_unlock_irq(&address_space->tree_lock);
227
228 swapcache_free(entry, page);
229 page_cache_release(page);
230}
231
232/*
233 * If we are the only user, then try to free up the swap cache.
234 *
235 * Its ok to check for PageSwapCache without the page lock
236 * here because we are going to recheck again inside
237 * try_to_free_swap() _with_ the lock.
238 * - Marcelo
239 */
240static inline void free_swap_cache(struct page *page)
241{
242 if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
243 try_to_free_swap(page);
244 unlock_page(page);
245 }
246}
247
248/*
249 * Perform a free_page(), also freeing any swap cache associated with
250 * this page if it is the last user of the page.
251 */
252void free_page_and_swap_cache(struct page *page)
253{
254 free_swap_cache(page);
255 page_cache_release(page);
256}
257
258/*
259 * Passed an array of pages, drop them all from swapcache and then release
260 * them. They are removed from the LRU and freed if this is their last use.
261 */
262void free_pages_and_swap_cache(struct page **pages, int nr)
263{
264 struct page **pagep = pages;
265
266 lru_add_drain();
267 while (nr) {
268 int todo = min(nr, PAGEVEC_SIZE);
269 int i;
270
271 for (i = 0; i < todo; i++)
272 free_swap_cache(pagep[i]);
273 release_pages(pagep, todo, 0);
274 pagep += todo;
275 nr -= todo;
276 }
277}
278
279/*
280 * Lookup a swap entry in the swap cache. A found page will be returned
281 * unlocked and with its refcount incremented - we rely on the kernel
282 * lock getting page table operations atomic even if we drop the page
283 * lock before returning.
284 */
285struct page * lookup_swap_cache(swp_entry_t entry)
286{
287 struct page *page;
288
289 page = find_get_page(swap_address_space(entry), entry.val);
290
291 if (page) {
292 INC_CACHE_INFO(find_success);
293 if (TestClearPageReadahead(page))
294 atomic_inc(&swapin_readahead_hits);
295 }
296
297 INC_CACHE_INFO(find_total);
298 return page;
299}
300
301/*
302 * Locate a page of swap in physical memory, reserving swap cache space
303 * and reading the disk if it is not already cached.
304 * A failure return means that either the page allocation failed or that
305 * the swap entry is no longer in use.
306 */
307struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
308 struct vm_area_struct *vma, unsigned long addr)
309{
310 struct page *found_page, *new_page = NULL;
311 int err;
312
313 do {
314 /*
315 * First check the swap cache. Since this is normally
316 * called after lookup_swap_cache() failed, re-calling
317 * that would confuse statistics.
318 */
319 found_page = find_get_page(swap_address_space(entry),
320 entry.val);
321 if (found_page)
322 break;
323
324 /*
325 * Get a new page to read into from swap.
326 */
327 if (!new_page) {
328 new_page = alloc_page_vma(gfp_mask, vma, addr);
329 if (!new_page)
330 break; /* Out of memory */
331 }
332
333 /*
334 * call radix_tree_preload() while we can wait.
335 */
336 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
337 if (err)
338 break;
339
340 /*
341 * Swap entry may have been freed since our caller observed it.
342 */
343 err = swapcache_prepare(entry);
344 if (err == -EEXIST) {
345 radix_tree_preload_end();
346 /*
347 * We might race against get_swap_page() and stumble
348 * across a SWAP_HAS_CACHE swap_map entry whose page
349 * has not been brought into the swapcache yet, while
350 * the other end is scheduled away waiting on discard
351 * I/O completion at scan_swap_map().
352 *
353 * In order to avoid turning this transitory state
354 * into a permanent loop around this -EEXIST case
355 * if !CONFIG_PREEMPT and the I/O completion happens
356 * to be waiting on the CPU waitqueue where we are now
357 * busy looping, we just conditionally invoke the
358 * scheduler here, if there are some more important
359 * tasks to run.
360 */
361 cond_resched();
362 continue;
363 }
364 if (err) { /* swp entry is obsolete ? */
365 radix_tree_preload_end();
366 break;
367 }
368
369 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
370 __set_page_locked(new_page);
371 SetPageSwapBacked(new_page);
372 err = __add_to_swap_cache(new_page, entry);
373 if (likely(!err)) {
374 radix_tree_preload_end();
375 /*
376 * Initiate read into locked page and return.
377 */
378 lru_cache_add_anon(new_page);
379 swap_readpage(new_page);
380 return new_page;
381 }
382 radix_tree_preload_end();
383 ClearPageSwapBacked(new_page);
384 __clear_page_locked(new_page);
385 /*
386 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
387 * clear SWAP_HAS_CACHE flag.
388 */
389 swapcache_free(entry, NULL);
390 } while (err != -ENOMEM);
391
392 if (new_page)
393 page_cache_release(new_page);
394 return found_page;
395}
396
397static unsigned long swapin_nr_pages(unsigned long offset)
398{
399 static unsigned long prev_offset;
400 unsigned int pages, max_pages, last_ra;
401 static atomic_t last_readahead_pages;
402
403 max_pages = 1 << ACCESS_ONCE(page_cluster);
404 if (max_pages <= 1)
405 return 1;
406
407 /*
408 * This heuristic has been found to work well on both sequential and
409 * random loads, swapping to hard disk or to SSD: please don't ask
410 * what the "+ 2" means, it just happens to work well, that's all.
411 */
412 pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
413 if (pages == 2) {
414 /*
415 * We can have no readahead hits to judge by: but must not get
416 * stuck here forever, so check for an adjacent offset instead
417 * (and don't even bother to check whether swap type is same).
418 */
419 if (offset != prev_offset + 1 && offset != prev_offset - 1)
420 pages = 1;
421 prev_offset = offset;
422 } else {
423 unsigned int roundup = 4;
424 while (roundup < pages)
425 roundup <<= 1;
426 pages = roundup;
427 }
428
429 if (pages > max_pages)
430 pages = max_pages;
431
432 /* Don't shrink readahead too fast */
433 last_ra = atomic_read(&last_readahead_pages) / 2;
434 if (pages < last_ra)
435 pages = last_ra;
436 atomic_set(&last_readahead_pages, pages);
437
438 return pages;
439}
440
441/**
442 * swapin_readahead - swap in pages in hope we need them soon
443 * @entry: swap entry of this memory
444 * @gfp_mask: memory allocation flags
445 * @vma: user vma this address belongs to
446 * @addr: target address for mempolicy
447 *
448 * Returns the struct page for entry and addr, after queueing swapin.
449 *
450 * Primitive swap readahead code. We simply read an aligned block of
451 * (1 << page_cluster) entries in the swap area. This method is chosen
452 * because it doesn't cost us any seek time. We also make sure to queue
453 * the 'original' request together with the readahead ones...
454 *
455 * This has been extended to use the NUMA policies from the mm triggering
456 * the readahead.
457 *
458 * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
459 */
460struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
461 struct vm_area_struct *vma, unsigned long addr)
462{
463 struct page *page;
464 unsigned long entry_offset = swp_offset(entry);
465 unsigned long offset = entry_offset;
466 unsigned long start_offset, end_offset;
467 unsigned long mask;
468 struct blk_plug plug;
469
470 mask = swapin_nr_pages(offset) - 1;
471 if (!mask)
472 goto skip;
473
474 /* Read a page_cluster sized and aligned cluster around offset. */
475 start_offset = offset & ~mask;
476 end_offset = offset | mask;
477 if (!start_offset) /* First page is swap header. */
478 start_offset++;
479
480 blk_start_plug(&plug);
481 for (offset = start_offset; offset <= end_offset ; offset++) {
482 /* Ok, do the async read-ahead now */
483 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
484 gfp_mask, vma, addr);
485 if (!page)
486 continue;
487 if (offset != entry_offset)
488 SetPageReadahead(page);
489 page_cache_release(page);
490 }
491 blk_finish_plug(&plug);
492
493 lru_add_drain(); /* Push any new pages onto the LRU now */
494skip:
495 return read_swap_cache_async(entry, gfp_mask, vma, addr);
496}
1/*
2 * linux/mm/swap_state.c
3 *
4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
5 * Swap reorganised 29.12.95, Stephen Tweedie
6 *
7 * Rewritten to use page cache, (C) 1998 Stephen Tweedie
8 */
9#include <linux/mm.h>
10#include <linux/gfp.h>
11#include <linux/kernel_stat.h>
12#include <linux/swap.h>
13#include <linux/swapops.h>
14#include <linux/init.h>
15#include <linux/pagemap.h>
16#include <linux/backing-dev.h>
17#include <linux/blkdev.h>
18#include <linux/pagevec.h>
19#include <linux/migrate.h>
20
21#include <asm/pgtable.h>
22
23/*
24 * swapper_space is a fiction, retained to simplify the path through
25 * vmscan's shrink_page_list.
26 */
27static const struct address_space_operations swap_aops = {
28 .writepage = swap_writepage,
29 .set_page_dirty = swap_set_page_dirty,
30#ifdef CONFIG_MIGRATION
31 .migratepage = migrate_page,
32#endif
33};
34
35struct address_space swapper_spaces[MAX_SWAPFILES] = {
36 [0 ... MAX_SWAPFILES - 1] = {
37 .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
38 .i_mmap_writable = ATOMIC_INIT(0),
39 .a_ops = &swap_aops,
40 }
41};
42
43#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
44
45static struct {
46 unsigned long add_total;
47 unsigned long del_total;
48 unsigned long find_success;
49 unsigned long find_total;
50} swap_cache_info;
51
52unsigned long total_swapcache_pages(void)
53{
54 int i;
55 unsigned long ret = 0;
56
57 for (i = 0; i < MAX_SWAPFILES; i++)
58 ret += swapper_spaces[i].nrpages;
59 return ret;
60}
61
62static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
63
64void show_swap_cache_info(void)
65{
66 printk("%lu pages in swap cache\n", total_swapcache_pages());
67 printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
68 swap_cache_info.add_total, swap_cache_info.del_total,
69 swap_cache_info.find_success, swap_cache_info.find_total);
70 printk("Free swap = %ldkB\n",
71 get_nr_swap_pages() << (PAGE_SHIFT - 10));
72 printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
73}
74
75/*
76 * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
77 * but sets SwapCache flag and private instead of mapping and index.
78 */
79int __add_to_swap_cache(struct page *page, swp_entry_t entry)
80{
81 int error;
82 struct address_space *address_space;
83
84 VM_BUG_ON_PAGE(!PageLocked(page), page);
85 VM_BUG_ON_PAGE(PageSwapCache(page), page);
86 VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
87
88 get_page(page);
89 SetPageSwapCache(page);
90 set_page_private(page, entry.val);
91
92 address_space = swap_address_space(entry);
93 spin_lock_irq(&address_space->tree_lock);
94 error = radix_tree_insert(&address_space->page_tree,
95 entry.val, page);
96 if (likely(!error)) {
97 address_space->nrpages++;
98 __inc_zone_page_state(page, NR_FILE_PAGES);
99 INC_CACHE_INFO(add_total);
100 }
101 spin_unlock_irq(&address_space->tree_lock);
102
103 if (unlikely(error)) {
104 /*
105 * Only the context which have set SWAP_HAS_CACHE flag
106 * would call add_to_swap_cache().
107 * So add_to_swap_cache() doesn't returns -EEXIST.
108 */
109 VM_BUG_ON(error == -EEXIST);
110 set_page_private(page, 0UL);
111 ClearPageSwapCache(page);
112 put_page(page);
113 }
114
115 return error;
116}
117
118
119int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
120{
121 int error;
122
123 error = radix_tree_maybe_preload(gfp_mask);
124 if (!error) {
125 error = __add_to_swap_cache(page, entry);
126 radix_tree_preload_end();
127 }
128 return error;
129}
130
131/*
132 * This must be called only on pages that have
133 * been verified to be in the swap cache.
134 */
135void __delete_from_swap_cache(struct page *page)
136{
137 swp_entry_t entry;
138 struct address_space *address_space;
139
140 VM_BUG_ON_PAGE(!PageLocked(page), page);
141 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
142 VM_BUG_ON_PAGE(PageWriteback(page), page);
143
144 entry.val = page_private(page);
145 address_space = swap_address_space(entry);
146 radix_tree_delete(&address_space->page_tree, page_private(page));
147 set_page_private(page, 0);
148 ClearPageSwapCache(page);
149 address_space->nrpages--;
150 __dec_zone_page_state(page, NR_FILE_PAGES);
151 INC_CACHE_INFO(del_total);
152}
153
154/**
155 * add_to_swap - allocate swap space for a page
156 * @page: page we want to move to swap
157 *
158 * Allocate swap space for the page and add the page to the
159 * swap cache. Caller needs to hold the page lock.
160 */
161int add_to_swap(struct page *page, struct list_head *list)
162{
163 swp_entry_t entry;
164 int err;
165
166 VM_BUG_ON_PAGE(!PageLocked(page), page);
167 VM_BUG_ON_PAGE(!PageUptodate(page), page);
168
169 entry = get_swap_page();
170 if (!entry.val)
171 return 0;
172
173 if (mem_cgroup_try_charge_swap(page, entry)) {
174 swapcache_free(entry);
175 return 0;
176 }
177
178 if (unlikely(PageTransHuge(page)))
179 if (unlikely(split_huge_page_to_list(page, list))) {
180 swapcache_free(entry);
181 return 0;
182 }
183
184 /*
185 * Radix-tree node allocations from PF_MEMALLOC contexts could
186 * completely exhaust the page allocator. __GFP_NOMEMALLOC
187 * stops emergency reserves from being allocated.
188 *
189 * TODO: this could cause a theoretical memory reclaim
190 * deadlock in the swap out path.
191 */
192 /*
193 * Add it to the swap cache.
194 */
195 err = add_to_swap_cache(page, entry,
196 __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
197
198 if (!err) {
199 return 1;
200 } else { /* -ENOMEM radix-tree allocation failure */
201 /*
202 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
203 * clear SWAP_HAS_CACHE flag.
204 */
205 swapcache_free(entry);
206 return 0;
207 }
208}
209
210/*
211 * This must be called only on pages that have
212 * been verified to be in the swap cache and locked.
213 * It will never put the page into the free list,
214 * the caller has a reference on the page.
215 */
216void delete_from_swap_cache(struct page *page)
217{
218 swp_entry_t entry;
219 struct address_space *address_space;
220
221 entry.val = page_private(page);
222
223 address_space = swap_address_space(entry);
224 spin_lock_irq(&address_space->tree_lock);
225 __delete_from_swap_cache(page);
226 spin_unlock_irq(&address_space->tree_lock);
227
228 swapcache_free(entry);
229 put_page(page);
230}
231
232/*
233 * If we are the only user, then try to free up the swap cache.
234 *
235 * Its ok to check for PageSwapCache without the page lock
236 * here because we are going to recheck again inside
237 * try_to_free_swap() _with_ the lock.
238 * - Marcelo
239 */
240static inline void free_swap_cache(struct page *page)
241{
242 if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
243 try_to_free_swap(page);
244 unlock_page(page);
245 }
246}
247
248/*
249 * Perform a free_page(), also freeing any swap cache associated with
250 * this page if it is the last user of the page.
251 */
252void free_page_and_swap_cache(struct page *page)
253{
254 free_swap_cache(page);
255 put_page(page);
256}
257
258/*
259 * Passed an array of pages, drop them all from swapcache and then release
260 * them. They are removed from the LRU and freed if this is their last use.
261 */
262void free_pages_and_swap_cache(struct page **pages, int nr)
263{
264 struct page **pagep = pages;
265 int i;
266
267 lru_add_drain();
268 for (i = 0; i < nr; i++)
269 free_swap_cache(pagep[i]);
270 release_pages(pagep, nr, false);
271}
272
273/*
274 * Lookup a swap entry in the swap cache. A found page will be returned
275 * unlocked and with its refcount incremented - we rely on the kernel
276 * lock getting page table operations atomic even if we drop the page
277 * lock before returning.
278 */
279struct page * lookup_swap_cache(swp_entry_t entry)
280{
281 struct page *page;
282
283 page = find_get_page(swap_address_space(entry), entry.val);
284
285 if (page) {
286 INC_CACHE_INFO(find_success);
287 if (TestClearPageReadahead(page))
288 atomic_inc(&swapin_readahead_hits);
289 }
290
291 INC_CACHE_INFO(find_total);
292 return page;
293}
294
295struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
296 struct vm_area_struct *vma, unsigned long addr,
297 bool *new_page_allocated)
298{
299 struct page *found_page, *new_page = NULL;
300 struct address_space *swapper_space = swap_address_space(entry);
301 int err;
302 *new_page_allocated = false;
303
304 do {
305 /*
306 * First check the swap cache. Since this is normally
307 * called after lookup_swap_cache() failed, re-calling
308 * that would confuse statistics.
309 */
310 found_page = find_get_page(swapper_space, entry.val);
311 if (found_page)
312 break;
313
314 /*
315 * Get a new page to read into from swap.
316 */
317 if (!new_page) {
318 new_page = alloc_page_vma(gfp_mask, vma, addr);
319 if (!new_page)
320 break; /* Out of memory */
321 }
322
323 /*
324 * call radix_tree_preload() while we can wait.
325 */
326 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
327 if (err)
328 break;
329
330 /*
331 * Swap entry may have been freed since our caller observed it.
332 */
333 err = swapcache_prepare(entry);
334 if (err == -EEXIST) {
335 radix_tree_preload_end();
336 /*
337 * We might race against get_swap_page() and stumble
338 * across a SWAP_HAS_CACHE swap_map entry whose page
339 * has not been brought into the swapcache yet, while
340 * the other end is scheduled away waiting on discard
341 * I/O completion at scan_swap_map().
342 *
343 * In order to avoid turning this transitory state
344 * into a permanent loop around this -EEXIST case
345 * if !CONFIG_PREEMPT and the I/O completion happens
346 * to be waiting on the CPU waitqueue where we are now
347 * busy looping, we just conditionally invoke the
348 * scheduler here, if there are some more important
349 * tasks to run.
350 */
351 cond_resched();
352 continue;
353 }
354 if (err) { /* swp entry is obsolete ? */
355 radix_tree_preload_end();
356 break;
357 }
358
359 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
360 __SetPageLocked(new_page);
361 SetPageSwapBacked(new_page);
362 err = __add_to_swap_cache(new_page, entry);
363 if (likely(!err)) {
364 radix_tree_preload_end();
365 /*
366 * Initiate read into locked page and return.
367 */
368 lru_cache_add_anon(new_page);
369 *new_page_allocated = true;
370 return new_page;
371 }
372 radix_tree_preload_end();
373 ClearPageSwapBacked(new_page);
374 __ClearPageLocked(new_page);
375 /*
376 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
377 * clear SWAP_HAS_CACHE flag.
378 */
379 swapcache_free(entry);
380 } while (err != -ENOMEM);
381
382 if (new_page)
383 put_page(new_page);
384 return found_page;
385}
386
387/*
388 * Locate a page of swap in physical memory, reserving swap cache space
389 * and reading the disk if it is not already cached.
390 * A failure return means that either the page allocation failed or that
391 * the swap entry is no longer in use.
392 */
393struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
394 struct vm_area_struct *vma, unsigned long addr)
395{
396 bool page_was_allocated;
397 struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
398 vma, addr, &page_was_allocated);
399
400 if (page_was_allocated)
401 swap_readpage(retpage);
402
403 return retpage;
404}
405
406static unsigned long swapin_nr_pages(unsigned long offset)
407{
408 static unsigned long prev_offset;
409 unsigned int pages, max_pages, last_ra;
410 static atomic_t last_readahead_pages;
411
412 max_pages = 1 << READ_ONCE(page_cluster);
413 if (max_pages <= 1)
414 return 1;
415
416 /*
417 * This heuristic has been found to work well on both sequential and
418 * random loads, swapping to hard disk or to SSD: please don't ask
419 * what the "+ 2" means, it just happens to work well, that's all.
420 */
421 pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
422 if (pages == 2) {
423 /*
424 * We can have no readahead hits to judge by: but must not get
425 * stuck here forever, so check for an adjacent offset instead
426 * (and don't even bother to check whether swap type is same).
427 */
428 if (offset != prev_offset + 1 && offset != prev_offset - 1)
429 pages = 1;
430 prev_offset = offset;
431 } else {
432 unsigned int roundup = 4;
433 while (roundup < pages)
434 roundup <<= 1;
435 pages = roundup;
436 }
437
438 if (pages > max_pages)
439 pages = max_pages;
440
441 /* Don't shrink readahead too fast */
442 last_ra = atomic_read(&last_readahead_pages) / 2;
443 if (pages < last_ra)
444 pages = last_ra;
445 atomic_set(&last_readahead_pages, pages);
446
447 return pages;
448}
449
450/**
451 * swapin_readahead - swap in pages in hope we need them soon
452 * @entry: swap entry of this memory
453 * @gfp_mask: memory allocation flags
454 * @vma: user vma this address belongs to
455 * @addr: target address for mempolicy
456 *
457 * Returns the struct page for entry and addr, after queueing swapin.
458 *
459 * Primitive swap readahead code. We simply read an aligned block of
460 * (1 << page_cluster) entries in the swap area. This method is chosen
461 * because it doesn't cost us any seek time. We also make sure to queue
462 * the 'original' request together with the readahead ones...
463 *
464 * This has been extended to use the NUMA policies from the mm triggering
465 * the readahead.
466 *
467 * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
468 */
469struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
470 struct vm_area_struct *vma, unsigned long addr)
471{
472 struct page *page;
473 unsigned long entry_offset = swp_offset(entry);
474 unsigned long offset = entry_offset;
475 unsigned long start_offset, end_offset;
476 unsigned long mask;
477 struct blk_plug plug;
478
479 mask = swapin_nr_pages(offset) - 1;
480 if (!mask)
481 goto skip;
482
483 /* Read a page_cluster sized and aligned cluster around offset. */
484 start_offset = offset & ~mask;
485 end_offset = offset | mask;
486 if (!start_offset) /* First page is swap header. */
487 start_offset++;
488
489 blk_start_plug(&plug);
490 for (offset = start_offset; offset <= end_offset ; offset++) {
491 /* Ok, do the async read-ahead now */
492 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
493 gfp_mask, vma, addr);
494 if (!page)
495 continue;
496 if (offset != entry_offset)
497 SetPageReadahead(page);
498 put_page(page);
499 }
500 blk_finish_plug(&plug);
501
502 lru_add_drain(); /* Push any new pages onto the LRU now */
503skip:
504 return read_swap_cache_async(entry, gfp_mask, vma, addr);
505}