2 * linux/mm/swap_state.c
4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
5 * Swap reorganised 29.12.95, Stephen Tweedie
7 * Rewritten to use page cache, (C) 1998 Stephen Tweedie
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>
21 #include <asm/pgtable.h>
24 * swapper_space is a fiction, retained to simplify the path through
25 * vmscan's shrink_page_list.
27 static 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,
35 struct 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),
43 #define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
46 unsigned long add_total;
47 unsigned long del_total;
48 unsigned long find_success;
49 unsigned long find_total;
52 unsigned long total_swapcache_pages(void)
55 unsigned long ret = 0;
57 for (i = 0; i < MAX_SWAPFILES; i++)
58 ret += swapper_spaces[i].nrpages;
62 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
64 void show_swap_cache_info(void)
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));
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.
79 int __add_to_swap_cache(struct page *page, swp_entry_t entry)
82 struct address_space *address_space;
84 VM_BUG_ON_PAGE(!PageLocked(page), page);
85 VM_BUG_ON_PAGE(PageSwapCache(page), page);
86 VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
89 SetPageSwapCache(page);
90 set_page_private(page, entry.val);
92 address_space = swap_address_space(entry);
93 spin_lock_irq(&address_space->tree_lock);
94 error = radix_tree_insert(&address_space->page_tree,
97 address_space->nrpages++;
98 __inc_zone_page_state(page, NR_FILE_PAGES);
99 INC_CACHE_INFO(add_total);
101 spin_unlock_irq(&address_space->tree_lock);
103 if (unlikely(error)) {
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.
109 VM_BUG_ON(error == -EEXIST);
110 set_page_private(page, 0UL);
111 ClearPageSwapCache(page);
112 page_cache_release(page);
119 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
123 error = radix_tree_maybe_preload(gfp_mask);
125 error = __add_to_swap_cache(page, entry);
126 radix_tree_preload_end();
132 * This must be called only on pages that have
133 * been verified to be in the swap cache.
135 void __delete_from_swap_cache(struct page *page)
138 struct address_space *address_space;
140 VM_BUG_ON_PAGE(!PageLocked(page), page);
141 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
142 VM_BUG_ON_PAGE(PageWriteback(page), page);
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);
155 * add_to_swap - allocate swap space for a page
156 * @page: page we want to move to swap
158 * Allocate swap space for the page and add the page to the
159 * swap cache. Caller needs to hold the page lock.
161 int add_to_swap(struct page *page, struct list_head *list)
166 VM_BUG_ON_PAGE(!PageLocked(page), page);
167 VM_BUG_ON_PAGE(!PageUptodate(page), page);
169 entry = get_swap_page();
173 if (unlikely(PageTransHuge(page)))
174 if (unlikely(split_huge_page_to_list(page, list))) {
175 swapcache_free(entry);
180 * Radix-tree node allocations from PF_MEMALLOC contexts could
181 * completely exhaust the page allocator. __GFP_NOMEMALLOC
182 * stops emergency reserves from being allocated.
184 * TODO: this could cause a theoretical memory reclaim
185 * deadlock in the swap out path.
188 * Add it to the swap cache and mark it dirty
190 err = add_to_swap_cache(page, entry,
191 __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
193 if (!err) { /* Success */
196 } else { /* -ENOMEM radix-tree allocation failure */
198 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
199 * clear SWAP_HAS_CACHE flag.
201 swapcache_free(entry);
207 * This must be called only on pages that have
208 * been verified to be in the swap cache and locked.
209 * It will never put the page into the free list,
210 * the caller has a reference on the page.
212 void delete_from_swap_cache(struct page *page)
215 struct address_space *address_space;
217 entry.val = page_private(page);
219 address_space = swap_address_space(entry);
220 spin_lock_irq(&address_space->tree_lock);
221 __delete_from_swap_cache(page);
222 spin_unlock_irq(&address_space->tree_lock);
224 swapcache_free(entry);
225 page_cache_release(page);
229 * If we are the only user, then try to free up the swap cache.
231 * Its ok to check for PageSwapCache without the page lock
232 * here because we are going to recheck again inside
233 * try_to_free_swap() _with_ the lock.
236 static inline void free_swap_cache(struct page *page)
238 if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
239 try_to_free_swap(page);
245 * Perform a free_page(), also freeing any swap cache associated with
246 * this page if it is the last user of the page.
248 void free_page_and_swap_cache(struct page *page)
250 free_swap_cache(page);
251 page_cache_release(page);
255 * Passed an array of pages, drop them all from swapcache and then release
256 * them. They are removed from the LRU and freed if this is their last use.
258 void free_pages_and_swap_cache(struct page **pages, int nr)
260 struct page **pagep = pages;
264 for (i = 0; i < nr; i++)
265 free_swap_cache(pagep[i]);
266 release_pages(pagep, nr, false);
270 * Lookup a swap entry in the swap cache. A found page will be returned
271 * unlocked and with its refcount incremented - we rely on the kernel
272 * lock getting page table operations atomic even if we drop the page
273 * lock before returning.
275 struct page * lookup_swap_cache(swp_entry_t entry)
279 page = find_get_page(swap_address_space(entry), entry.val);
282 INC_CACHE_INFO(find_success);
283 if (TestClearPageReadahead(page))
284 atomic_inc(&swapin_readahead_hits);
287 INC_CACHE_INFO(find_total);
291 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
292 struct vm_area_struct *vma, unsigned long addr,
293 bool *new_page_allocated)
295 struct page *found_page, *new_page = NULL;
296 struct address_space *swapper_space = swap_address_space(entry);
298 *new_page_allocated = false;
302 * First check the swap cache. Since this is normally
303 * called after lookup_swap_cache() failed, re-calling
304 * that would confuse statistics.
306 found_page = find_get_page(swapper_space, entry.val);
311 * Get a new page to read into from swap.
314 new_page = alloc_page_vma(gfp_mask, vma, addr);
316 break; /* Out of memory */
320 * call radix_tree_preload() while we can wait.
322 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
327 * Swap entry may have been freed since our caller observed it.
329 err = swapcache_prepare(entry);
330 if (err == -EEXIST) {
331 radix_tree_preload_end();
333 * We might race against get_swap_page() and stumble
334 * across a SWAP_HAS_CACHE swap_map entry whose page
335 * has not been brought into the swapcache yet, while
336 * the other end is scheduled away waiting on discard
337 * I/O completion at scan_swap_map().
339 * In order to avoid turning this transitory state
340 * into a permanent loop around this -EEXIST case
341 * if !CONFIG_PREEMPT and the I/O completion happens
342 * to be waiting on the CPU waitqueue where we are now
343 * busy looping, we just conditionally invoke the
344 * scheduler here, if there are some more important
350 if (err) { /* swp entry is obsolete ? */
351 radix_tree_preload_end();
355 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
356 __set_page_locked(new_page);
357 SetPageSwapBacked(new_page);
358 err = __add_to_swap_cache(new_page, entry);
360 radix_tree_preload_end();
362 * Initiate read into locked page and return.
364 lru_cache_add_anon(new_page);
365 *new_page_allocated = true;
368 radix_tree_preload_end();
369 ClearPageSwapBacked(new_page);
370 __clear_page_locked(new_page);
372 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
373 * clear SWAP_HAS_CACHE flag.
375 swapcache_free(entry);
376 } while (err != -ENOMEM);
379 page_cache_release(new_page);
384 * Locate a page of swap in physical memory, reserving swap cache space
385 * and reading the disk if it is not already cached.
386 * A failure return means that either the page allocation failed or that
387 * the swap entry is no longer in use.
389 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
390 struct vm_area_struct *vma, unsigned long addr)
392 bool page_was_allocated;
393 struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
394 vma, addr, &page_was_allocated);
396 if (page_was_allocated)
397 swap_readpage(retpage);
402 static unsigned long swapin_nr_pages(unsigned long offset)
404 static unsigned long prev_offset;
405 unsigned int pages, max_pages, last_ra;
406 static atomic_t last_readahead_pages;
408 max_pages = 1 << READ_ONCE(page_cluster);
413 * This heuristic has been found to work well on both sequential and
414 * random loads, swapping to hard disk or to SSD: please don't ask
415 * what the "+ 2" means, it just happens to work well, that's all.
417 pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
420 * We can have no readahead hits to judge by: but must not get
421 * stuck here forever, so check for an adjacent offset instead
422 * (and don't even bother to check whether swap type is same).
424 if (offset != prev_offset + 1 && offset != prev_offset - 1)
426 prev_offset = offset;
428 unsigned int roundup = 4;
429 while (roundup < pages)
434 if (pages > max_pages)
437 /* Don't shrink readahead too fast */
438 last_ra = atomic_read(&last_readahead_pages) / 2;
441 atomic_set(&last_readahead_pages, pages);
447 * swapin_readahead - swap in pages in hope we need them soon
448 * @entry: swap entry of this memory
449 * @gfp_mask: memory allocation flags
450 * @vma: user vma this address belongs to
451 * @addr: target address for mempolicy
453 * Returns the struct page for entry and addr, after queueing swapin.
455 * Primitive swap readahead code. We simply read an aligned block of
456 * (1 << page_cluster) entries in the swap area. This method is chosen
457 * because it doesn't cost us any seek time. We also make sure to queue
458 * the 'original' request together with the readahead ones...
460 * This has been extended to use the NUMA policies from the mm triggering
463 * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
465 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
466 struct vm_area_struct *vma, unsigned long addr)
469 unsigned long entry_offset = swp_offset(entry);
470 unsigned long offset = entry_offset;
471 unsigned long start_offset, end_offset;
473 struct blk_plug plug;
475 mask = swapin_nr_pages(offset) - 1;
479 /* Read a page_cluster sized and aligned cluster around offset. */
480 start_offset = offset & ~mask;
481 end_offset = offset | mask;
482 if (!start_offset) /* First page is swap header. */
485 blk_start_plug(&plug);
486 for (offset = start_offset; offset <= end_offset ; offset++) {
487 /* Ok, do the async read-ahead now */
488 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
489 gfp_mask, vma, addr);
492 if (offset != entry_offset)
493 SetPageReadahead(page);
494 page_cache_release(page);
496 blk_finish_plug(&plug);
498 lru_add_drain(); /* Push any new pages onto the LRU now */
500 return read_swap_cache_async(entry, gfp_mask, vma, addr);