summaryrefslogtreecommitdiff
path: root/mm/swap_state.c (plain)
blob: d1f04ea23c048cb2b03fccab5b10726cd0bc3577
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 /* swap cache doesn't use writeback related tags */
41 .flags = 1 << AS_NO_WRITEBACK_TAGS,
42 }
43};
44
45#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
46
47static struct {
48 unsigned long add_total;
49 unsigned long del_total;
50 unsigned long find_success;
51 unsigned long find_total;
52} swap_cache_info;
53
54unsigned long total_swapcache_pages(void)
55{
56 int i;
57 unsigned long ret = 0;
58
59 for (i = 0; i < MAX_SWAPFILES; i++)
60 ret += swapper_spaces[i].nrpages;
61 return ret;
62}
63
64static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
65
66void show_swap_cache_info(void)
67{
68 printk("%lu pages in swap cache\n", total_swapcache_pages());
69 printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
70 swap_cache_info.add_total, swap_cache_info.del_total,
71 swap_cache_info.find_success, swap_cache_info.find_total);
72 printk("Free swap = %ldkB\n",
73 get_nr_swap_pages() << (PAGE_SHIFT - 10));
74 printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
75}
76
77/*
78 * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
79 * but sets SwapCache flag and private instead of mapping and index.
80 */
81int __add_to_swap_cache(struct page *page, swp_entry_t entry)
82{
83 int error;
84 struct address_space *address_space;
85
86 VM_BUG_ON_PAGE(!PageLocked(page), page);
87 VM_BUG_ON_PAGE(PageSwapCache(page), page);
88 VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
89
90 get_page(page);
91 SetPageSwapCache(page);
92 set_page_private(page, entry.val);
93
94 address_space = swap_address_space(entry);
95 spin_lock_irq(&address_space->tree_lock);
96 error = radix_tree_insert(&address_space->page_tree,
97 swp_offset(entry), page);
98 if (likely(!error)) {
99 address_space->nrpages++;
100 __inc_node_page_state(page, NR_FILE_PAGES);
101 INC_CACHE_INFO(add_total);
102 }
103 spin_unlock_irq(&address_space->tree_lock);
104
105 if (unlikely(error)) {
106 /*
107 * Only the context which have set SWAP_HAS_CACHE flag
108 * would call add_to_swap_cache().
109 * So add_to_swap_cache() doesn't returns -EEXIST.
110 */
111 VM_BUG_ON(error == -EEXIST);
112 set_page_private(page, 0UL);
113 ClearPageSwapCache(page);
114 put_page(page);
115 }
116
117 return error;
118}
119
120
121int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
122{
123 int error;
124
125 error = radix_tree_maybe_preload(gfp_mask);
126 if (!error) {
127 error = __add_to_swap_cache(page, entry);
128 radix_tree_preload_end();
129 }
130 return error;
131}
132
133/*
134 * This must be called only on pages that have
135 * been verified to be in the swap cache.
136 */
137void __delete_from_swap_cache(struct page *page)
138{
139 swp_entry_t entry;
140 struct address_space *address_space;
141
142 VM_BUG_ON_PAGE(!PageLocked(page), page);
143 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
144 VM_BUG_ON_PAGE(PageWriteback(page), page);
145
146 entry.val = page_private(page);
147 address_space = swap_address_space(entry);
148 radix_tree_delete(&address_space->page_tree, swp_offset(entry));
149 set_page_private(page, 0);
150 ClearPageSwapCache(page);
151 address_space->nrpages--;
152 __dec_node_page_state(page, NR_FILE_PAGES);
153 INC_CACHE_INFO(del_total);
154}
155
156/**
157 * add_to_swap - allocate swap space for a page
158 * @page: page we want to move to swap
159 *
160 * Allocate swap space for the page and add the page to the
161 * swap cache. Caller needs to hold the page lock.
162 */
163int add_to_swap(struct page *page, struct list_head *list)
164{
165 swp_entry_t entry;
166 int err;
167
168 VM_BUG_ON_PAGE(!PageLocked(page), page);
169 VM_BUG_ON_PAGE(!PageUptodate(page), page);
170
171 entry = get_swap_page();
172 if (!entry.val)
173 return 0;
174
175 if (mem_cgroup_try_charge_swap(page, entry)) {
176 swapcache_free(entry);
177 return 0;
178 }
179
180 if (unlikely(PageTransHuge(page)))
181 if (unlikely(split_huge_page_to_list(page, list))) {
182 swapcache_free(entry);
183 return 0;
184 }
185
186 /*
187 * Radix-tree 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(page, entry,
198 __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
199
200 if (!err) {
201 return 1;
202 } else { /* -ENOMEM radix-tree allocation failure */
203 /*
204 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
205 * clear SWAP_HAS_CACHE flag.
206 */
207 swapcache_free(entry);
208 return 0;
209 }
210}
211
212/*
213 * This must be called only on pages that have
214 * been verified to be in the swap cache and locked.
215 * It will never put the page into the free list,
216 * the caller has a reference on the page.
217 */
218void delete_from_swap_cache(struct page *page)
219{
220 swp_entry_t entry;
221 struct address_space *address_space;
222
223 entry.val = page_private(page);
224
225 address_space = swap_address_space(entry);
226 spin_lock_irq(&address_space->tree_lock);
227 __delete_from_swap_cache(page);
228 spin_unlock_irq(&address_space->tree_lock);
229
230 swapcache_free(entry);
231 put_page(page);
232}
233
234/*
235 * If we are the only user, then try to free up the swap cache.
236 *
237 * Its ok to check for PageSwapCache without the page lock
238 * here because we are going to recheck again inside
239 * try_to_free_swap() _with_ the lock.
240 * - Marcelo
241 */
242static inline void free_swap_cache(struct page *page)
243{
244 if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
245 try_to_free_swap(page);
246 unlock_page(page);
247 }
248}
249
250/*
251 * Perform a free_page(), also freeing any swap cache associated with
252 * this page if it is the last user of the page.
253 */
254void free_page_and_swap_cache(struct page *page)
255{
256 free_swap_cache(page);
257 if (!is_huge_zero_page(page))
258 put_page(page);
259}
260
261/*
262 * Passed an array of pages, drop them all from swapcache and then release
263 * them. They are removed from the LRU and freed if this is their last use.
264 */
265void free_pages_and_swap_cache(struct page **pages, int nr)
266{
267 struct page **pagep = pages;
268 int i;
269
270 lru_add_drain();
271 for (i = 0; i < nr; i++)
272 free_swap_cache(pagep[i]);
273 release_pages(pagep, nr, false);
274}
275
276/*
277 * Lookup a swap entry in the swap cache. A found page will be returned
278 * unlocked and with its refcount incremented - we rely on the kernel
279 * lock getting page table operations atomic even if we drop the page
280 * lock before returning.
281 */
282struct page * lookup_swap_cache(swp_entry_t entry)
283{
284 struct page *page;
285
286 page = find_get_page(swap_address_space(entry), swp_offset(entry));
287
288 if (page) {
289 INC_CACHE_INFO(find_success);
290 if (TestClearPageReadahead(page))
291 atomic_inc(&swapin_readahead_hits);
292 }
293
294 INC_CACHE_INFO(find_total);
295 return page;
296}
297
298struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
299 struct vm_area_struct *vma, unsigned long addr,
300 bool *new_page_allocated)
301{
302 struct page *found_page, *new_page = NULL;
303 struct address_space *swapper_space = swap_address_space(entry);
304 int err;
305 *new_page_allocated = false;
306
307 do {
308 /*
309 * First check the swap cache. Since this is normally
310 * called after lookup_swap_cache() failed, re-calling
311 * that would confuse statistics.
312 */
313 found_page = find_get_page(swapper_space, swp_offset(entry));
314 if (found_page)
315 break;
316
317 /*
318 * Get a new page to read into from swap.
319 */
320 if (!new_page) {
321 #ifdef CONFIG_AMLOGIC_CMA
322 new_page = alloc_page_vma(gfp_mask | __GFP_BDEV,
323 vma, addr);
324 #else
325 new_page = alloc_page_vma(gfp_mask, vma, addr);
326 #endif
327 if (!new_page)
328 break; /* Out of memory */
329 }
330
331 /*
332 * call radix_tree_preload() while we can wait.
333 */
334 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
335 if (err)
336 break;
337
338 /*
339 * Swap entry may have been freed since our caller observed it.
340 */
341 err = swapcache_prepare(entry);
342 if (err == -EEXIST) {
343 radix_tree_preload_end();
344 /*
345 * We might race against get_swap_page() and stumble
346 * across a SWAP_HAS_CACHE swap_map entry whose page
347 * has not been brought into the swapcache yet, while
348 * the other end is scheduled away waiting on discard
349 * I/O completion at scan_swap_map().
350 *
351 * In order to avoid turning this transitory state
352 * into a permanent loop around this -EEXIST case
353 * if !CONFIG_PREEMPT and the I/O completion happens
354 * to be waiting on the CPU waitqueue where we are now
355 * busy looping, we just conditionally invoke the
356 * scheduler here, if there are some more important
357 * tasks to run.
358 */
359 cond_resched();
360 continue;
361 }
362 if (err) { /* swp entry is obsolete ? */
363 radix_tree_preload_end();
364 break;
365 }
366
367 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
368 __SetPageLocked(new_page);
369 __SetPageSwapBacked(new_page);
370 err = __add_to_swap_cache(new_page, entry);
371 if (likely(!err)) {
372 radix_tree_preload_end();
373 /*
374 * Initiate read into locked page and return.
375 */
376 SetPageWorkingset(new_page);
377 lru_cache_add_anon(new_page);
378 *new_page_allocated = true;
379 return new_page;
380 }
381 radix_tree_preload_end();
382 __ClearPageLocked(new_page);
383 /*
384 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
385 * clear SWAP_HAS_CACHE flag.
386 */
387 swapcache_free(entry);
388 } while (err != -ENOMEM);
389
390 if (new_page)
391 put_page(new_page);
392 return found_page;
393}
394
395/*
396 * Locate a page of swap in physical memory, reserving swap cache space
397 * and reading the disk if it is not already cached.
398 * A failure return means that either the page allocation failed or that
399 * the swap entry is no longer in use.
400 */
401struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
402 struct vm_area_struct *vma, unsigned long addr)
403{
404 bool page_was_allocated;
405 struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
406 vma, addr, &page_was_allocated);
407
408 if (page_was_allocated)
409 swap_readpage(retpage);
410
411 return retpage;
412}
413
414static unsigned long swapin_nr_pages(unsigned long offset)
415{
416 static unsigned long prev_offset;
417 unsigned int pages, max_pages, last_ra;
418 static atomic_t last_readahead_pages;
419
420 max_pages = 1 << READ_ONCE(page_cluster);
421 if (max_pages <= 1)
422 return 1;
423
424 /*
425 * This heuristic has been found to work well on both sequential and
426 * random loads, swapping to hard disk or to SSD: please don't ask
427 * what the "+ 2" means, it just happens to work well, that's all.
428 */
429 pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
430 if (pages == 2) {
431 /*
432 * We can have no readahead hits to judge by: but must not get
433 * stuck here forever, so check for an adjacent offset instead
434 * (and don't even bother to check whether swap type is same).
435 */
436 if (offset != prev_offset + 1 && offset != prev_offset - 1)
437 pages = 1;
438 prev_offset = offset;
439 } else {
440 unsigned int roundup = 4;
441 while (roundup < pages)
442 roundup <<= 1;
443 pages = roundup;
444 }
445
446 if (pages > max_pages)
447 pages = max_pages;
448
449 /* Don't shrink readahead too fast */
450 last_ra = atomic_read(&last_readahead_pages) / 2;
451 if (pages < last_ra)
452 pages = last_ra;
453 atomic_set(&last_readahead_pages, pages);
454
455 return pages;
456}
457
458/**
459 * swapin_readahead - swap in pages in hope we need them soon
460 * @entry: swap entry of this memory
461 * @gfp_mask: memory allocation flags
462 * @vma: user vma this address belongs to
463 * @addr: target address for mempolicy
464 *
465 * Returns the struct page for entry and addr, after queueing swapin.
466 *
467 * Primitive swap readahead code. We simply read an aligned block of
468 * (1 << page_cluster) entries in the swap area. This method is chosen
469 * because it doesn't cost us any seek time. We also make sure to queue
470 * the 'original' request together with the readahead ones...
471 *
472 * This has been extended to use the NUMA policies from the mm triggering
473 * the readahead.
474 *
475 * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
476 */
477struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
478 struct vm_area_struct *vma, unsigned long addr)
479{
480 struct page *page;
481 unsigned long entry_offset = swp_offset(entry);
482 unsigned long offset = entry_offset;
483 unsigned long start_offset, end_offset;
484 unsigned long mask;
485 struct blk_plug plug;
486
487 mask = swapin_nr_pages(offset) - 1;
488 if (!mask)
489 goto skip;
490
491 /* Read a page_cluster sized and aligned cluster around offset. */
492 start_offset = offset & ~mask;
493 end_offset = offset | mask;
494 if (!start_offset) /* First page is swap header. */
495 start_offset++;
496
497 blk_start_plug(&plug);
498 for (offset = start_offset; offset <= end_offset ; offset++) {
499 /* Ok, do the async read-ahead now */
500 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
501 gfp_mask, vma, addr);
502 if (!page)
503 continue;
504 if (offset != entry_offset)
505 SetPageReadahead(page);
506 put_page(page);
507 }
508 blk_finish_plug(&plug);
509
510 lru_add_drain(); /* Push any new pages onto the LRU now */
511skip:
512 return read_swap_cache_async(entry, gfp_mask, vma, addr);
513}
514