Root/mm/swap_state.c

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/module.h>
10#include <linux/mm.h>
11#include <linux/gfp.h>
12#include <linux/kernel_stat.h>
13#include <linux/swap.h>
14#include <linux/swapops.h>
15#include <linux/init.h>
16#include <linux/pagemap.h>
17#include <linux/buffer_head.h>
18#include <linux/backing-dev.h>
19#include <linux/pagevec.h>
20#include <linux/migrate.h>
21#include <linux/page_cgroup.h>
22
23#include <asm/pgtable.h>
24
25/*
26 * swapper_space is a fiction, retained to simplify the path through
27 * vmscan's shrink_page_list, to make sync_page look nicer, and to allow
28 * future use of radix_tree tags in the swap cache.
29 */
30static const struct address_space_operations swap_aops = {
31    .writepage = swap_writepage,
32    .sync_page = block_sync_page,
33    .set_page_dirty = __set_page_dirty_nobuffers,
34    .migratepage = migrate_page,
35};
36
37static struct backing_dev_info swap_backing_dev_info = {
38    .name = "swap",
39    .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
40    .unplug_io_fn = swap_unplug_io_fn,
41};
42
43struct address_space swapper_space = {
44    .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
45    .tree_lock = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
46    .a_ops = &swap_aops,
47    .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
48    .backing_dev_info = &swap_backing_dev_info,
49};
50
51#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
52
53static struct {
54    unsigned long add_total;
55    unsigned long del_total;
56    unsigned long find_success;
57    unsigned long find_total;
58} swap_cache_info;
59
60void show_swap_cache_info(void)
61{
62    printk("%lu pages in swap cache\n", total_swapcache_pages);
63    printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
64        swap_cache_info.add_total, swap_cache_info.del_total,
65        swap_cache_info.find_success, swap_cache_info.find_total);
66    printk("Free swap = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10));
67    printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
68}
69
70/*
71 * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
72 * but sets SwapCache flag and private instead of mapping and index.
73 */
74static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
75{
76    int error;
77
78    VM_BUG_ON(!PageLocked(page));
79    VM_BUG_ON(PageSwapCache(page));
80    VM_BUG_ON(!PageSwapBacked(page));
81
82    page_cache_get(page);
83    SetPageSwapCache(page);
84    set_page_private(page, entry.val);
85
86    spin_lock_irq(&swapper_space.tree_lock);
87    error = radix_tree_insert(&swapper_space.page_tree, entry.val, page);
88    if (likely(!error)) {
89        total_swapcache_pages++;
90        __inc_zone_page_state(page, NR_FILE_PAGES);
91        INC_CACHE_INFO(add_total);
92    }
93    spin_unlock_irq(&swapper_space.tree_lock);
94
95    if (unlikely(error)) {
96        /*
97         * Only the context which have set SWAP_HAS_CACHE flag
98         * would call add_to_swap_cache().
99         * So add_to_swap_cache() doesn't returns -EEXIST.
100         */
101        VM_BUG_ON(error == -EEXIST);
102        set_page_private(page, 0UL);
103        ClearPageSwapCache(page);
104        page_cache_release(page);
105    }
106
107    return error;
108}
109
110
111int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
112{
113    int error;
114
115    error = radix_tree_preload(gfp_mask);
116    if (!error) {
117        error = __add_to_swap_cache(page, entry);
118        radix_tree_preload_end();
119    }
120    return error;
121}
122
123/*
124 * This must be called only on pages that have
125 * been verified to be in the swap cache.
126 */
127void __delete_from_swap_cache(struct page *page)
128{
129    VM_BUG_ON(!PageLocked(page));
130    VM_BUG_ON(!PageSwapCache(page));
131    VM_BUG_ON(PageWriteback(page));
132
133    radix_tree_delete(&swapper_space.page_tree, page_private(page));
134    set_page_private(page, 0);
135    ClearPageSwapCache(page);
136    total_swapcache_pages--;
137    __dec_zone_page_state(page, NR_FILE_PAGES);
138    INC_CACHE_INFO(del_total);
139}
140
141/**
142 * add_to_swap - allocate swap space for a page
143 * @page: page we want to move to swap
144 *
145 * Allocate swap space for the page and add the page to the
146 * swap cache. Caller needs to hold the page lock.
147 */
148int add_to_swap(struct page *page)
149{
150    swp_entry_t entry;
151    int err;
152
153    VM_BUG_ON(!PageLocked(page));
154    VM_BUG_ON(!PageUptodate(page));
155
156    entry = get_swap_page();
157    if (!entry.val)
158        return 0;
159
160    /*
161     * Radix-tree node allocations from PF_MEMALLOC contexts could
162     * completely exhaust the page allocator. __GFP_NOMEMALLOC
163     * stops emergency reserves from being allocated.
164     *
165     * TODO: this could cause a theoretical memory reclaim
166     * deadlock in the swap out path.
167     */
168    /*
169     * Add it to the swap cache and mark it dirty
170     */
171    err = add_to_swap_cache(page, entry,
172            __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
173
174    if (!err) { /* Success */
175        SetPageDirty(page);
176        return 1;
177    } else { /* -ENOMEM radix-tree allocation failure */
178        /*
179         * add_to_swap_cache() doesn't return -EEXIST, so we can safely
180         * clear SWAP_HAS_CACHE flag.
181         */
182        swapcache_free(entry, NULL);
183        return 0;
184    }
185}
186
187/*
188 * This must be called only on pages that have
189 * been verified to be in the swap cache and locked.
190 * It will never put the page into the free list,
191 * the caller has a reference on the page.
192 */
193void delete_from_swap_cache(struct page *page)
194{
195    swp_entry_t entry;
196
197    entry.val = page_private(page);
198
199    spin_lock_irq(&swapper_space.tree_lock);
200    __delete_from_swap_cache(page);
201    spin_unlock_irq(&swapper_space.tree_lock);
202
203    swapcache_free(entry, page);
204    page_cache_release(page);
205}
206
207/*
208 * If we are the only user, then try to free up the swap cache.
209 *
210 * Its ok to check for PageSwapCache without the page lock
211 * here because we are going to recheck again inside
212 * try_to_free_swap() _with_ the lock.
213 * - Marcelo
214 */
215static inline void free_swap_cache(struct page *page)
216{
217    if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
218        try_to_free_swap(page);
219        unlock_page(page);
220    }
221}
222
223/*
224 * Perform a free_page(), also freeing any swap cache associated with
225 * this page if it is the last user of the page.
226 */
227void free_page_and_swap_cache(struct page *page)
228{
229    free_swap_cache(page);
230    page_cache_release(page);
231}
232
233/*
234 * Passed an array of pages, drop them all from swapcache and then release
235 * them. They are removed from the LRU and freed if this is their last use.
236 */
237void free_pages_and_swap_cache(struct page **pages, int nr)
238{
239    struct page **pagep = pages;
240
241    lru_add_drain();
242    while (nr) {
243        int todo = min(nr, PAGEVEC_SIZE);
244        int i;
245
246        for (i = 0; i < todo; i++)
247            free_swap_cache(pagep[i]);
248        release_pages(pagep, todo, 0);
249        pagep += todo;
250        nr -= todo;
251    }
252}
253
254/*
255 * Lookup a swap entry in the swap cache. A found page will be returned
256 * unlocked and with its refcount incremented - we rely on the kernel
257 * lock getting page table operations atomic even if we drop the page
258 * lock before returning.
259 */
260struct page * lookup_swap_cache(swp_entry_t entry)
261{
262    struct page *page;
263
264    page = find_get_page(&swapper_space, entry.val);
265
266    if (page)
267        INC_CACHE_INFO(find_success);
268
269    INC_CACHE_INFO(find_total);
270    return page;
271}
272
273/*
274 * Locate a page of swap in physical memory, reserving swap cache space
275 * and reading the disk if it is not already cached.
276 * A failure return means that either the page allocation failed or that
277 * the swap entry is no longer in use.
278 */
279struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
280            struct vm_area_struct *vma, unsigned long addr)
281{
282    struct page *found_page, *new_page = NULL;
283    int err;
284
285    do {
286        /*
287         * First check the swap cache. Since this is normally
288         * called after lookup_swap_cache() failed, re-calling
289         * that would confuse statistics.
290         */
291        found_page = find_get_page(&swapper_space, entry.val);
292        if (found_page)
293            break;
294
295        /*
296         * Get a new page to read into from swap.
297         */
298        if (!new_page) {
299            new_page = alloc_page_vma(gfp_mask, vma, addr);
300            if (!new_page)
301                break; /* Out of memory */
302        }
303
304        /*
305         * call radix_tree_preload() while we can wait.
306         */
307        err = radix_tree_preload(gfp_mask & GFP_KERNEL);
308        if (err)
309            break;
310
311        /*
312         * Swap entry may have been freed since our caller observed it.
313         */
314        err = swapcache_prepare(entry);
315        if (err == -EEXIST) { /* seems racy */
316            radix_tree_preload_end();
317            continue;
318        }
319        if (err) { /* swp entry is obsolete ? */
320            radix_tree_preload_end();
321            break;
322        }
323
324        /* May fail (-ENOMEM) if radix-tree node allocation failed. */
325        __set_page_locked(new_page);
326        SetPageSwapBacked(new_page);
327        err = __add_to_swap_cache(new_page, entry);
328        if (likely(!err)) {
329            radix_tree_preload_end();
330            /*
331             * Initiate read into locked page and return.
332             */
333            lru_cache_add_anon(new_page);
334            swap_readpage(new_page);
335            return new_page;
336        }
337        radix_tree_preload_end();
338        ClearPageSwapBacked(new_page);
339        __clear_page_locked(new_page);
340        /*
341         * add_to_swap_cache() doesn't return -EEXIST, so we can safely
342         * clear SWAP_HAS_CACHE flag.
343         */
344        swapcache_free(entry, NULL);
345    } while (err != -ENOMEM);
346
347    if (new_page)
348        page_cache_release(new_page);
349    return found_page;
350}
351
352/**
353 * swapin_readahead - swap in pages in hope we need them soon
354 * @entry: swap entry of this memory
355 * @gfp_mask: memory allocation flags
356 * @vma: user vma this address belongs to
357 * @addr: target address for mempolicy
358 *
359 * Returns the struct page for entry and addr, after queueing swapin.
360 *
361 * Primitive swap readahead code. We simply read an aligned block of
362 * (1 << page_cluster) entries in the swap area. This method is chosen
363 * because it doesn't cost us any seek time. We also make sure to queue
364 * the 'original' request together with the readahead ones...
365 *
366 * This has been extended to use the NUMA policies from the mm triggering
367 * the readahead.
368 *
369 * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
370 */
371struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
372            struct vm_area_struct *vma, unsigned long addr)
373{
374    int nr_pages;
375    struct page *page;
376    unsigned long offset;
377    unsigned long end_offset;
378
379    /*
380     * Get starting offset for readaround, and number of pages to read.
381     * Adjust starting address by readbehind (for NUMA interleave case)?
382     * No, it's very unlikely that swap layout would follow vma layout,
383     * more likely that neighbouring swap pages came from the same node:
384     * so use the same "addr" to choose the same node for each swap read.
385     */
386    nr_pages = valid_swaphandles(entry, &offset);
387    for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
388        /* Ok, do the async read-ahead now */
389        page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
390                        gfp_mask, vma, addr);
391        if (!page)
392            break;
393        page_cache_release(page);
394    }
395    lru_add_drain(); /* Push any new pages onto the LRU now */
396    return read_swap_cache_async(entry, gfp_mask, vma, addr);
397}
398

Archive Download this file



interactive