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>
20 #include <linux/vmalloc.h>
21 #include <linux/swap_slots.h>
22 #include <linux/huge_mm.h>
24 #include <asm/pgtable.h>
27 * swapper_space is a fiction, retained to simplify the path through
28 * vmscan's shrink_page_list.
30 static const struct address_space_operations swap_aops = {
31 .writepage = swap_writepage,
32 .set_page_dirty = swap_set_page_dirty,
33 #ifdef CONFIG_MIGRATION
34 .migratepage = migrate_page,
38 struct address_space *swapper_spaces[MAX_SWAPFILES];
39 static unsigned int nr_swapper_spaces[MAX_SWAPFILES];
41 #define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
42 #define ADD_CACHE_INFO(x, nr) do { swap_cache_info.x += (nr); } while (0)
45 unsigned long add_total;
46 unsigned long del_total;
47 unsigned long find_success;
48 unsigned long find_total;
51 unsigned long total_swapcache_pages(void)
53 unsigned int i, j, nr;
54 unsigned long ret = 0;
55 struct address_space *spaces;
58 for (i = 0; i < MAX_SWAPFILES; i++) {
60 * The corresponding entries in nr_swapper_spaces and
61 * swapper_spaces will be reused only after at least
62 * one grace period. So it is impossible for them
63 * belongs to different usage.
65 nr = nr_swapper_spaces[i];
66 spaces = rcu_dereference(swapper_spaces[i]);
69 for (j = 0; j < nr; j++)
70 ret += spaces[j].nrpages;
76 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
78 void show_swap_cache_info(void)
80 printk("%lu pages in swap cache\n", total_swapcache_pages());
81 printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
82 swap_cache_info.add_total, swap_cache_info.del_total,
83 swap_cache_info.find_success, swap_cache_info.find_total);
84 printk("Free swap = %ldkB\n",
85 get_nr_swap_pages() << (PAGE_SHIFT - 10));
86 printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
90 * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
91 * but sets SwapCache flag and private instead of mapping and index.
93 int __add_to_swap_cache(struct page *page, swp_entry_t entry)
95 int error, i, nr = hpage_nr_pages(page);
96 struct address_space *address_space;
97 pgoff_t idx = swp_offset(entry);
99 VM_BUG_ON_PAGE(!PageLocked(page), page);
100 VM_BUG_ON_PAGE(PageSwapCache(page), page);
101 VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
103 page_ref_add(page, nr);
104 SetPageSwapCache(page);
106 address_space = swap_address_space(entry);
107 spin_lock_irq(&address_space->tree_lock);
108 for (i = 0; i < nr; i++) {
109 set_page_private(page + i, entry.val + i);
110 error = radix_tree_insert(&address_space->page_tree,
115 if (likely(!error)) {
116 address_space->nrpages += nr;
117 __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
118 ADD_CACHE_INFO(add_total, nr);
121 * Only the context which have set SWAP_HAS_CACHE flag
122 * would call add_to_swap_cache().
123 * So add_to_swap_cache() doesn't returns -EEXIST.
125 VM_BUG_ON(error == -EEXIST);
126 set_page_private(page + i, 0UL);
128 radix_tree_delete(&address_space->page_tree, idx + i);
129 set_page_private(page + i, 0UL);
131 ClearPageSwapCache(page);
132 page_ref_sub(page, nr);
134 spin_unlock_irq(&address_space->tree_lock);
140 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
144 error = radix_tree_maybe_preload_order(gfp_mask, compound_order(page));
146 error = __add_to_swap_cache(page, entry);
147 radix_tree_preload_end();
153 * This must be called only on pages that have
154 * been verified to be in the swap cache.
156 void __delete_from_swap_cache(struct page *page)
158 struct address_space *address_space;
159 int i, nr = hpage_nr_pages(page);
163 VM_BUG_ON_PAGE(!PageLocked(page), page);
164 VM_BUG_ON_PAGE(!PageSwapCache(page), page);
165 VM_BUG_ON_PAGE(PageWriteback(page), page);
167 entry.val = page_private(page);
168 address_space = swap_address_space(entry);
169 idx = swp_offset(entry);
170 for (i = 0; i < nr; i++) {
171 radix_tree_delete(&address_space->page_tree, idx + i);
172 set_page_private(page + i, 0);
174 ClearPageSwapCache(page);
175 address_space->nrpages -= nr;
176 __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
177 ADD_CACHE_INFO(del_total, nr);
181 * add_to_swap - allocate swap space for a page
182 * @page: page we want to move to swap
184 * Allocate swap space for the page and add the page to the
185 * swap cache. Caller needs to hold the page lock.
187 int add_to_swap(struct page *page, struct list_head *list)
192 VM_BUG_ON_PAGE(!PageLocked(page), page);
193 VM_BUG_ON_PAGE(!PageUptodate(page), page);
196 entry = get_swap_page(page);
199 if (mem_cgroup_try_charge_swap(page, entry))
203 * Radix-tree node allocations from PF_MEMALLOC contexts could
204 * completely exhaust the page allocator. __GFP_NOMEMALLOC
205 * stops emergency reserves from being allocated.
207 * TODO: this could cause a theoretical memory reclaim
208 * deadlock in the swap out path.
211 * Add it to the swap cache.
213 err = add_to_swap_cache(page, entry,
214 __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
215 /* -ENOMEM radix-tree allocation failure */
218 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
219 * clear SWAP_HAS_CACHE flag.
223 if (PageTransHuge(page)) {
224 err = split_huge_page_to_list(page, list);
226 delete_from_swap_cache(page);
234 if (PageTransHuge(page))
235 swapcache_free_cluster(entry);
237 swapcache_free(entry);
239 if (PageTransHuge(page) && !split_huge_page_to_list(page, list))
245 * This must be called only on pages that have
246 * been verified to be in the swap cache and locked.
247 * It will never put the page into the free list,
248 * the caller has a reference on the page.
250 void delete_from_swap_cache(struct page *page)
253 struct address_space *address_space;
255 entry.val = page_private(page);
257 address_space = swap_address_space(entry);
258 spin_lock_irq(&address_space->tree_lock);
259 __delete_from_swap_cache(page);
260 spin_unlock_irq(&address_space->tree_lock);
262 if (PageTransHuge(page))
263 swapcache_free_cluster(entry);
265 swapcache_free(entry);
267 page_ref_sub(page, hpage_nr_pages(page));
271 * If we are the only user, then try to free up the swap cache.
273 * Its ok to check for PageSwapCache without the page lock
274 * here because we are going to recheck again inside
275 * try_to_free_swap() _with_ the lock.
278 static inline void free_swap_cache(struct page *page)
280 if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
281 try_to_free_swap(page);
287 * Perform a free_page(), also freeing any swap cache associated with
288 * this page if it is the last user of the page.
290 void free_page_and_swap_cache(struct page *page)
292 free_swap_cache(page);
293 if (!is_huge_zero_page(page))
298 * Passed an array of pages, drop them all from swapcache and then release
299 * them. They are removed from the LRU and freed if this is their last use.
301 void free_pages_and_swap_cache(struct page **pages, int nr)
303 struct page **pagep = pages;
307 for (i = 0; i < nr; i++)
308 free_swap_cache(pagep[i]);
309 release_pages(pagep, nr, false);
313 * Lookup a swap entry in the swap cache. A found page will be returned
314 * unlocked and with its refcount incremented - we rely on the kernel
315 * lock getting page table operations atomic even if we drop the page
316 * lock before returning.
318 struct page * lookup_swap_cache(swp_entry_t entry)
322 page = find_get_page(swap_address_space(entry), swp_offset(entry));
324 if (page && likely(!PageTransCompound(page))) {
325 INC_CACHE_INFO(find_success);
326 if (TestClearPageReadahead(page))
327 atomic_inc(&swapin_readahead_hits);
330 INC_CACHE_INFO(find_total);
334 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
335 struct vm_area_struct *vma, unsigned long addr,
336 bool *new_page_allocated)
338 struct page *found_page, *new_page = NULL;
339 struct address_space *swapper_space = swap_address_space(entry);
341 *new_page_allocated = false;
345 * First check the swap cache. Since this is normally
346 * called after lookup_swap_cache() failed, re-calling
347 * that would confuse statistics.
349 found_page = find_get_page(swapper_space, swp_offset(entry));
354 * Just skip read ahead for unused swap slot.
355 * During swap_off when swap_slot_cache is disabled,
356 * we have to handle the race between putting
357 * swap entry in swap cache and marking swap slot
358 * as SWAP_HAS_CACHE. That's done in later part of code or
359 * else swap_off will be aborted if we return NULL.
361 if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
365 * Get a new page to read into from swap.
368 new_page = alloc_page_vma(gfp_mask, vma, addr);
370 break; /* Out of memory */
374 * call radix_tree_preload() while we can wait.
376 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
381 * Swap entry may have been freed since our caller observed it.
383 err = swapcache_prepare(entry);
384 if (err == -EEXIST) {
385 radix_tree_preload_end();
387 * We might race against get_swap_page() and stumble
388 * across a SWAP_HAS_CACHE swap_map entry whose page
389 * has not been brought into the swapcache yet.
394 if (err) { /* swp entry is obsolete ? */
395 radix_tree_preload_end();
399 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
400 __SetPageLocked(new_page);
401 __SetPageSwapBacked(new_page);
402 err = __add_to_swap_cache(new_page, entry);
404 radix_tree_preload_end();
406 * Initiate read into locked page and return.
408 lru_cache_add_anon(new_page);
409 *new_page_allocated = true;
412 radix_tree_preload_end();
413 __ClearPageLocked(new_page);
415 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
416 * clear SWAP_HAS_CACHE flag.
418 swapcache_free(entry);
419 } while (err != -ENOMEM);
427 * Locate a page of swap in physical memory, reserving swap cache space
428 * and reading the disk if it is not already cached.
429 * A failure return means that either the page allocation failed or that
430 * the swap entry is no longer in use.
432 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
433 struct vm_area_struct *vma, unsigned long addr)
435 bool page_was_allocated;
436 struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
437 vma, addr, &page_was_allocated);
439 if (page_was_allocated)
440 swap_readpage(retpage);
445 static unsigned long swapin_nr_pages(unsigned long offset)
447 static unsigned long prev_offset;
448 unsigned int pages, max_pages, last_ra;
449 static atomic_t last_readahead_pages;
451 max_pages = 1 << READ_ONCE(page_cluster);
456 * This heuristic has been found to work well on both sequential and
457 * random loads, swapping to hard disk or to SSD: please don't ask
458 * what the "+ 2" means, it just happens to work well, that's all.
460 pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
463 * We can have no readahead hits to judge by: but must not get
464 * stuck here forever, so check for an adjacent offset instead
465 * (and don't even bother to check whether swap type is same).
467 if (offset != prev_offset + 1 && offset != prev_offset - 1)
469 prev_offset = offset;
471 unsigned int roundup = 4;
472 while (roundup < pages)
477 if (pages > max_pages)
480 /* Don't shrink readahead too fast */
481 last_ra = atomic_read(&last_readahead_pages) / 2;
484 atomic_set(&last_readahead_pages, pages);
490 * swapin_readahead - swap in pages in hope we need them soon
491 * @entry: swap entry of this memory
492 * @gfp_mask: memory allocation flags
493 * @vma: user vma this address belongs to
494 * @addr: target address for mempolicy
496 * Returns the struct page for entry and addr, after queueing swapin.
498 * Primitive swap readahead code. We simply read an aligned block of
499 * (1 << page_cluster) entries in the swap area. This method is chosen
500 * because it doesn't cost us any seek time. We also make sure to queue
501 * the 'original' request together with the readahead ones...
503 * This has been extended to use the NUMA policies from the mm triggering
506 * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
508 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
509 struct vm_area_struct *vma, unsigned long addr)
512 unsigned long entry_offset = swp_offset(entry);
513 unsigned long offset = entry_offset;
514 unsigned long start_offset, end_offset;
516 struct blk_plug plug;
518 mask = swapin_nr_pages(offset) - 1;
522 /* Read a page_cluster sized and aligned cluster around offset. */
523 start_offset = offset & ~mask;
524 end_offset = offset | mask;
525 if (!start_offset) /* First page is swap header. */
528 blk_start_plug(&plug);
529 for (offset = start_offset; offset <= end_offset ; offset++) {
530 /* Ok, do the async read-ahead now */
531 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
532 gfp_mask, vma, addr);
535 if (offset != entry_offset && likely(!PageTransCompound(page)))
536 SetPageReadahead(page);
539 blk_finish_plug(&plug);
541 lru_add_drain(); /* Push any new pages onto the LRU now */
543 return read_swap_cache_async(entry, gfp_mask, vma, addr);
546 int init_swap_address_space(unsigned int type, unsigned long nr_pages)
548 struct address_space *spaces, *space;
551 nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
552 spaces = kvzalloc(sizeof(struct address_space) * nr, GFP_KERNEL);
555 for (i = 0; i < nr; i++) {
557 INIT_RADIX_TREE(&space->page_tree, GFP_ATOMIC|__GFP_NOWARN);
558 atomic_set(&space->i_mmap_writable, 0);
559 space->a_ops = &swap_aops;
560 /* swap cache doesn't use writeback related tags */
561 mapping_set_no_writeback_tags(space);
562 spin_lock_init(&space->tree_lock);
564 nr_swapper_spaces[type] = nr;
565 rcu_assign_pointer(swapper_spaces[type], spaces);
570 void exit_swap_address_space(unsigned int type)
572 struct address_space *spaces;
574 spaces = swapper_spaces[type];
575 nr_swapper_spaces[type] = 0;
576 rcu_assign_pointer(swapper_spaces[type], NULL);