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/page_cgroup.h>
22 #include <asm/pgtable.h>
25 * swapper_space is a fiction, retained to simplify the path through
26 * vmscan's shrink_page_list.
28 static const struct address_space_operations swap_aops
= {
29 .writepage
= swap_writepage
,
30 .set_page_dirty
= swap_set_page_dirty
,
31 .migratepage
= migrate_page
,
34 static struct backing_dev_info swap_backing_dev_info
= {
36 .capabilities
= BDI_CAP_NO_ACCT_AND_WRITEBACK
| BDI_CAP_SWAP_BACKED
,
39 struct address_space swapper_spaces
[MAX_SWAPFILES
] = {
40 [0 ... MAX_SWAPFILES
- 1] = {
41 .page_tree
= RADIX_TREE_INIT(GFP_ATOMIC
|__GFP_NOWARN
),
43 .backing_dev_info
= &swap_backing_dev_info
,
47 #define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
50 unsigned long add_total
;
51 unsigned long del_total
;
52 unsigned long find_success
;
53 unsigned long find_total
;
56 unsigned long total_swapcache_pages(void)
59 unsigned long ret
= 0;
61 for (i
= 0; i
< MAX_SWAPFILES
; i
++)
62 ret
+= swapper_spaces
[i
].nrpages
;
66 void show_swap_cache_info(void)
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));
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.
81 int __add_to_swap_cache(struct page
*page
, swp_entry_t entry
)
84 struct address_space
*address_space
;
86 VM_BUG_ON(!PageLocked(page
));
87 VM_BUG_ON(PageSwapCache(page
));
88 VM_BUG_ON(!PageSwapBacked(page
));
91 SetPageSwapCache(page
);
92 set_page_private(page
, entry
.val
);
94 address_space
= swap_address_space(entry
);
95 spin_lock_irq(&address_space
->tree_lock
);
96 error
= radix_tree_insert(&address_space
->page_tree
,
99 address_space
->nrpages
++;
100 __inc_zone_page_state(page
, NR_FILE_PAGES
);
101 INC_CACHE_INFO(add_total
);
103 spin_unlock_irq(&address_space
->tree_lock
);
105 if (unlikely(error
)) {
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.
111 VM_BUG_ON(error
== -EEXIST
);
112 set_page_private(page
, 0UL);
113 ClearPageSwapCache(page
);
114 page_cache_release(page
);
121 int add_to_swap_cache(struct page
*page
, swp_entry_t entry
, gfp_t gfp_mask
)
125 error
= radix_tree_preload(gfp_mask
);
127 error
= __add_to_swap_cache(page
, entry
);
128 radix_tree_preload_end();
134 * This must be called only on pages that have
135 * been verified to be in the swap cache.
137 void __delete_from_swap_cache(struct page
*page
)
140 struct address_space
*address_space
;
142 VM_BUG_ON(!PageLocked(page
));
143 VM_BUG_ON(!PageSwapCache(page
));
144 VM_BUG_ON(PageWriteback(page
));
146 entry
.val
= page_private(page
);
147 address_space
= swap_address_space(entry
);
148 radix_tree_delete(&address_space
->page_tree
, page_private(page
));
149 set_page_private(page
, 0);
150 ClearPageSwapCache(page
);
151 address_space
->nrpages
--;
152 __dec_zone_page_state(page
, NR_FILE_PAGES
);
153 INC_CACHE_INFO(del_total
);
157 * add_to_swap - allocate swap space for a page
158 * @page: page we want to move to swap
160 * Allocate swap space for the page and add the page to the
161 * swap cache. Caller needs to hold the page lock.
163 int add_to_swap(struct page
*page
, struct list_head
*list
)
168 VM_BUG_ON(!PageLocked(page
));
169 VM_BUG_ON(!PageUptodate(page
));
172 entry
= get_swap_page();
174 entry
= get_swap_page_by_memcg(page
);
179 if (unlikely(PageTransHuge(page
)))
180 if (unlikely(split_huge_page_to_list(page
, list
))) {
181 swapcache_free(entry
, NULL
);
186 * Radix-tree node allocations from PF_MEMALLOC contexts could
187 * completely exhaust the page allocator. __GFP_NOMEMALLOC
188 * stops emergency reserves from being allocated.
190 * TODO: this could cause a theoretical memory reclaim
191 * deadlock in the swap out path.
194 * Add it to the swap cache and mark it dirty
196 err
= add_to_swap_cache(page
, entry
,
197 __GFP_HIGH
|__GFP_NOMEMALLOC
|__GFP_NOWARN
);
199 if (!err
) { /* Success */
202 } else { /* -ENOMEM radix-tree allocation failure */
204 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
205 * clear SWAP_HAS_CACHE flag.
207 swapcache_free(entry
, NULL
);
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.
218 void delete_from_swap_cache(struct page
*page
)
221 struct address_space
*address_space
;
223 entry
.val
= page_private(page
);
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
);
230 swapcache_free(entry
, page
);
231 page_cache_release(page
);
235 * If we are the only user, then try to free up the swap cache.
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.
242 static inline void free_swap_cache(struct page
*page
)
244 if (PageSwapCache(page
) && !page_mapped(page
) && trylock_page(page
)) {
245 try_to_free_swap(page
);
251 * Perform a free_page(), also freeing any swap cache associated with
252 * this page if it is the last user of the page.
254 void free_page_and_swap_cache(struct page
*page
)
256 free_swap_cache(page
);
257 page_cache_release(page
);
261 * Passed an array of pages, drop them all from swapcache and then release
262 * them. They are removed from the LRU and freed if this is their last use.
264 void free_pages_and_swap_cache(struct page
**pages
, int nr
)
266 struct page
**pagep
= pages
;
270 int todo
= min(nr
, PAGEVEC_SIZE
);
273 for (i
= 0; i
< todo
; i
++)
274 free_swap_cache(pagep
[i
]);
275 release_pages(pagep
, todo
, 0);
282 * Lookup a swap entry in the swap cache. A found page will be returned
283 * unlocked and with its refcount incremented - we rely on the kernel
284 * lock getting page table operations atomic even if we drop the page
285 * lock before returning.
287 struct page
* lookup_swap_cache(swp_entry_t entry
)
291 page
= find_get_page(swap_address_space(entry
), entry
.val
);
294 INC_CACHE_INFO(find_success
);
296 INC_CACHE_INFO(find_total
);
301 * Locate a page of swap in physical memory, reserving swap cache space
302 * and reading the disk if it is not already cached.
303 * A failure return means that either the page allocation failed or that
304 * the swap entry is no longer in use.
306 struct page
*read_swap_cache_async(swp_entry_t entry
, gfp_t gfp_mask
,
307 struct vm_area_struct
*vma
, unsigned long addr
)
309 struct page
*found_page
, *new_page
= NULL
;
314 * First check the swap cache. Since this is normally
315 * called after lookup_swap_cache() failed, re-calling
316 * that would confuse statistics.
318 found_page
= find_get_page(swap_address_space(entry
),
324 * Get a new page to read into from swap.
327 new_page
= alloc_page_vma(gfp_mask
, vma
, addr
);
329 break; /* Out of memory */
333 * call radix_tree_preload() while we can wait.
335 err
= radix_tree_preload(gfp_mask
& GFP_KERNEL
);
340 * Swap entry may have been freed since our caller observed it.
342 err
= swapcache_prepare(entry
);
343 if (err
== -EEXIST
) {
344 radix_tree_preload_end();
346 * We might race against get_swap_page() and stumble
347 * across a SWAP_HAS_CACHE swap_map entry whose page
348 * has not been brought into the swapcache yet, while
349 * the other end is scheduled away waiting on discard
350 * I/O completion at scan_swap_map().
352 * In order to avoid turning this transitory state
353 * into a permanent loop around this -EEXIST case
354 * if !CONFIG_PREEMPT and the I/O completion happens
355 * to be waiting on the CPU waitqueue where we are now
356 * busy looping, we just conditionally invoke the
357 * scheduler here, if there are some more important
363 if (err
) { /* swp entry is obsolete ? */
364 radix_tree_preload_end();
368 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
369 __set_page_locked(new_page
);
370 SetPageSwapBacked(new_page
);
371 err
= __add_to_swap_cache(new_page
, entry
);
373 radix_tree_preload_end();
375 * Initiate read into locked page and return.
377 lru_cache_add_anon(new_page
);
378 swap_readpage(new_page
);
381 radix_tree_preload_end();
382 ClearPageSwapBacked(new_page
);
383 __clear_page_locked(new_page
);
385 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
386 * clear SWAP_HAS_CACHE flag.
388 swapcache_free(entry
, NULL
);
389 } while (err
!= -ENOMEM
);
392 page_cache_release(new_page
);
397 * swapin_readahead - swap in pages in hope we need them soon
398 * @entry: swap entry of this memory
399 * @gfp_mask: memory allocation flags
400 * @vma: user vma this address belongs to
401 * @addr: target address for mempolicy
403 * Returns the struct page for entry and addr, after queueing swapin.
405 * Primitive swap readahead code. We simply read an aligned block of
406 * (1 << page_cluster) entries in the swap area. This method is chosen
407 * because it doesn't cost us any seek time. We also make sure to queue
408 * the 'original' request together with the readahead ones...
410 * This has been extended to use the NUMA policies from the mm triggering
413 * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
415 struct page
*swapin_readahead(swp_entry_t entry
, gfp_t gfp_mask
,
416 struct vm_area_struct
*vma
, unsigned long addr
)
419 unsigned long offset
= swp_offset(entry
);
420 unsigned long start_offset
, end_offset
;
421 unsigned long mask
= (1UL << page_cluster
) - 1;
422 struct blk_plug plug
;
424 /* Read a page_cluster sized and aligned cluster around offset. */
425 start_offset
= offset
& ~mask
;
426 end_offset
= offset
| mask
;
427 if (!start_offset
) /* First page is swap header. */
430 blk_start_plug(&plug
);
431 for (offset
= start_offset
; offset
<= end_offset
; offset
++) {
432 /* Ok, do the async read-ahead now */
433 page
= read_swap_cache_async(swp_entry(swp_type(entry
), offset
),
434 gfp_mask
, vma
, addr
);
437 page_cache_release(page
);
439 blk_finish_plug(&plug
);
441 lru_add_drain(); /* Push any new pages onto the LRU now */
442 return read_swap_cache_async(entry
, gfp_mask
, vma
, addr
);