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/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#include <linux/page_cgroup.h>
21
22#include <asm/pgtable.h>
23
24/*
25 * swapper_space is a fiction, retained to simplify the path through
26 * vmscan's shrink_page_list.
27 */
28static const struct address_space_operations swap_aops = {
29    .writepage = swap_writepage,
30    .set_page_dirty = swap_set_page_dirty,
31    .migratepage = migrate_page,
32};
33
34static struct backing_dev_info swap_backing_dev_info = {
35    .name = "swap",
36    .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
37};
38
39struct address_space swapper_spaces[MAX_SWAPFILES] = {
40    [0 ... MAX_SWAPFILES - 1] = {
41        .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
42        .a_ops = &swap_aops,
43        .backing_dev_info = &swap_backing_dev_info,
44    }
45};
46
47#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
48
49static struct {
50    unsigned long add_total;
51    unsigned long del_total;
52    unsigned long find_success;
53    unsigned long find_total;
54} swap_cache_info;
55
56unsigned long total_swapcache_pages(void)
57{
58    int i;
59    unsigned long ret = 0;
60
61    for (i = 0; i < MAX_SWAPFILES; i++)
62        ret += swapper_spaces[i].nrpages;
63    return ret;
64}
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(!PageLocked(page));
87    VM_BUG_ON(PageSwapCache(page));
88    VM_BUG_ON(!PageSwapBacked(page));
89
90    page_cache_get(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                    entry.val, page);
98    if (likely(!error)) {
99        address_space->nrpages++;
100        __inc_zone_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        page_cache_release(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(!PageLocked(page));
143    VM_BUG_ON(!PageSwapCache(page));
144    VM_BUG_ON(PageWriteback(page));
145
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);
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(!PageLocked(page));
169    VM_BUG_ON(!PageUptodate(page));
170
171    entry = get_swap_page();
172    if (!entry.val)
173        return 0;
174
175    if (unlikely(PageTransHuge(page)))
176        if (unlikely(split_huge_page_to_list(page, list))) {
177            swapcache_free(entry, NULL);
178            return 0;
179        }
180
181    /*
182     * Radix-tree node allocations from PF_MEMALLOC contexts could
183     * completely exhaust the page allocator. __GFP_NOMEMALLOC
184     * stops emergency reserves from being allocated.
185     *
186     * TODO: this could cause a theoretical memory reclaim
187     * deadlock in the swap out path.
188     */
189    /*
190     * Add it to the swap cache and mark it dirty
191     */
192    err = add_to_swap_cache(page, entry,
193            __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
194
195    if (!err) { /* Success */
196        SetPageDirty(page);
197        return 1;
198    } else { /* -ENOMEM radix-tree allocation failure */
199        /*
200         * add_to_swap_cache() doesn't return -EEXIST, so we can safely
201         * clear SWAP_HAS_CACHE flag.
202         */
203        swapcache_free(entry, NULL);
204        return 0;
205    }
206}
207
208/*
209 * This must be called only on pages that have
210 * been verified to be in the swap cache and locked.
211 * It will never put the page into the free list,
212 * the caller has a reference on the page.
213 */
214void delete_from_swap_cache(struct page *page)
215{
216    swp_entry_t entry;
217    struct address_space *address_space;
218
219    entry.val = page_private(page);
220
221    address_space = swap_address_space(entry);
222    spin_lock_irq(&address_space->tree_lock);
223    __delete_from_swap_cache(page);
224    spin_unlock_irq(&address_space->tree_lock);
225
226    swapcache_free(entry, page);
227    page_cache_release(page);
228}
229
230/*
231 * If we are the only user, then try to free up the swap cache.
232 *
233 * Its ok to check for PageSwapCache without the page lock
234 * here because we are going to recheck again inside
235 * try_to_free_swap() _with_ the lock.
236 * - Marcelo
237 */
238static inline void free_swap_cache(struct page *page)
239{
240    if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
241        try_to_free_swap(page);
242        unlock_page(page);
243    }
244}
245
246/*
247 * Perform a free_page(), also freeing any swap cache associated with
248 * this page if it is the last user of the page.
249 */
250void free_page_and_swap_cache(struct page *page)
251{
252    free_swap_cache(page);
253    page_cache_release(page);
254}
255
256/*
257 * Passed an array of pages, drop them all from swapcache and then release
258 * them. They are removed from the LRU and freed if this is their last use.
259 */
260void free_pages_and_swap_cache(struct page **pages, int nr)
261{
262    struct page **pagep = pages;
263
264    lru_add_drain();
265    while (nr) {
266        int todo = min(nr, PAGEVEC_SIZE);
267        int i;
268
269        for (i = 0; i < todo; i++)
270            free_swap_cache(pagep[i]);
271        release_pages(pagep, todo, 0);
272        pagep += todo;
273        nr -= todo;
274    }
275}
276
277/*
278 * Lookup a swap entry in the swap cache. A found page will be returned
279 * unlocked and with its refcount incremented - we rely on the kernel
280 * lock getting page table operations atomic even if we drop the page
281 * lock before returning.
282 */
283struct page * lookup_swap_cache(swp_entry_t entry)
284{
285    struct page *page;
286
287    page = find_get_page(swap_address_space(entry), entry.val);
288
289    if (page)
290        INC_CACHE_INFO(find_success);
291
292    INC_CACHE_INFO(find_total);
293    return page;
294}
295
296/*
297 * Locate a page of swap in physical memory, reserving swap cache space
298 * and reading the disk if it is not already cached.
299 * A failure return means that either the page allocation failed or that
300 * the swap entry is no longer in use.
301 */
302struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
303            struct vm_area_struct *vma, unsigned long addr)
304{
305    struct page *found_page, *new_page = NULL;
306    int err;
307
308    do {
309        /*
310         * First check the swap cache. Since this is normally
311         * called after lookup_swap_cache() failed, re-calling
312         * that would confuse statistics.
313         */
314        found_page = find_get_page(swap_address_space(entry),
315                    entry.val);
316        if (found_page)
317            break;
318
319        /*
320         * Get a new page to read into from swap.
321         */
322        if (!new_page) {
323            new_page = alloc_page_vma(gfp_mask, vma, addr);
324            if (!new_page)
325                break; /* Out of memory */
326        }
327
328        /*
329         * call radix_tree_preload() while we can wait.
330         */
331        err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
332        if (err)
333            break;
334
335        /*
336         * Swap entry may have been freed since our caller observed it.
337         */
338        err = swapcache_prepare(entry);
339        if (err == -EEXIST) {
340            radix_tree_preload_end();
341            /*
342             * We might race against get_swap_page() and stumble
343             * across a SWAP_HAS_CACHE swap_map entry whose page
344             * has not been brought into the swapcache yet, while
345             * the other end is scheduled away waiting on discard
346             * I/O completion at scan_swap_map().
347             *
348             * In order to avoid turning this transitory state
349             * into a permanent loop around this -EEXIST case
350             * if !CONFIG_PREEMPT and the I/O completion happens
351             * to be waiting on the CPU waitqueue where we are now
352             * busy looping, we just conditionally invoke the
353             * scheduler here, if there are some more important
354             * tasks to run.
355             */
356            cond_resched();
357            continue;
358        }
359        if (err) { /* swp entry is obsolete ? */
360            radix_tree_preload_end();
361            break;
362        }
363
364        /* May fail (-ENOMEM) if radix-tree node allocation failed. */
365        __set_page_locked(new_page);
366        SetPageSwapBacked(new_page);
367        err = __add_to_swap_cache(new_page, entry);
368        if (likely(!err)) {
369            radix_tree_preload_end();
370            /*
371             * Initiate read into locked page and return.
372             */
373            lru_cache_add_anon(new_page);
374            swap_readpage(new_page);
375            return new_page;
376        }
377        radix_tree_preload_end();
378        ClearPageSwapBacked(new_page);
379        __clear_page_locked(new_page);
380        /*
381         * add_to_swap_cache() doesn't return -EEXIST, so we can safely
382         * clear SWAP_HAS_CACHE flag.
383         */
384        swapcache_free(entry, NULL);
385    } while (err != -ENOMEM);
386
387    if (new_page)
388        page_cache_release(new_page);
389    return found_page;
390}
391
392/**
393 * swapin_readahead - swap in pages in hope we need them soon
394 * @entry: swap entry of this memory
395 * @gfp_mask: memory allocation flags
396 * @vma: user vma this address belongs to
397 * @addr: target address for mempolicy
398 *
399 * Returns the struct page for entry and addr, after queueing swapin.
400 *
401 * Primitive swap readahead code. We simply read an aligned block of
402 * (1 << page_cluster) entries in the swap area. This method is chosen
403 * because it doesn't cost us any seek time. We also make sure to queue
404 * the 'original' request together with the readahead ones...
405 *
406 * This has been extended to use the NUMA policies from the mm triggering
407 * the readahead.
408 *
409 * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
410 */
411struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
412            struct vm_area_struct *vma, unsigned long addr)
413{
414    struct page *page;
415    unsigned long offset = swp_offset(entry);
416    unsigned long start_offset, end_offset;
417    unsigned long mask = (1UL << page_cluster) - 1;
418    struct blk_plug plug;
419
420    /* Read a page_cluster sized and aligned cluster around offset. */
421    start_offset = offset & ~mask;
422    end_offset = offset | mask;
423    if (!start_offset) /* First page is swap header. */
424        start_offset++;
425
426    blk_start_plug(&plug);
427    for (offset = start_offset; offset <= end_offset ; offset++) {
428        /* Ok, do the async read-ahead now */
429        page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
430                        gfp_mask, vma, addr);
431        if (!page)
432            continue;
433        page_cache_release(page);
434    }
435    blk_finish_plug(&plug);
436
437    lru_add_drain(); /* Push any new pages onto the LRU now */
438    return read_swap_cache_async(entry, gfp_mask, vma, addr);
439}
440

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