Root/mm/frontswap.c

1/*
2 * Frontswap frontend
3 *
4 * This code provides the generic "frontend" layer to call a matching
5 * "backend" driver implementation of frontswap. See
6 * Documentation/vm/frontswap.txt for more information.
7 *
8 * Copyright (C) 2009-2012 Oracle Corp. All rights reserved.
9 * Author: Dan Magenheimer
10 *
11 * This work is licensed under the terms of the GNU GPL, version 2.
12 */
13
14#include <linux/mman.h>
15#include <linux/swap.h>
16#include <linux/swapops.h>
17#include <linux/security.h>
18#include <linux/module.h>
19#include <linux/debugfs.h>
20#include <linux/frontswap.h>
21#include <linux/swapfile.h>
22
23/*
24 * frontswap_ops is set by frontswap_register_ops to contain the pointers
25 * to the frontswap "backend" implementation functions.
26 */
27static struct frontswap_ops frontswap_ops __read_mostly;
28
29/*
30 * This global enablement flag reduces overhead on systems where frontswap_ops
31 * has not been registered, so is preferred to the slower alternative: a
32 * function call that checks a non-global.
33 */
34bool frontswap_enabled __read_mostly;
35EXPORT_SYMBOL(frontswap_enabled);
36
37/*
38 * If enabled, frontswap_store will return failure even on success. As
39 * a result, the swap subsystem will always write the page to swap, in
40 * effect converting frontswap into a writethrough cache. In this mode,
41 * there is no direct reduction in swap writes, but a frontswap backend
42 * can unilaterally "reclaim" any pages in use with no data loss, thus
43 * providing increases control over maximum memory usage due to frontswap.
44 */
45static bool frontswap_writethrough_enabled __read_mostly;
46
47#ifdef CONFIG_DEBUG_FS
48/*
49 * Counters available via /sys/kernel/debug/frontswap (if debugfs is
50 * properly configured). These are for information only so are not protected
51 * against increment races.
52 */
53static u64 frontswap_loads;
54static u64 frontswap_succ_stores;
55static u64 frontswap_failed_stores;
56static u64 frontswap_invalidates;
57
58static inline void inc_frontswap_loads(void) {
59    frontswap_loads++;
60}
61static inline void inc_frontswap_succ_stores(void) {
62    frontswap_succ_stores++;
63}
64static inline void inc_frontswap_failed_stores(void) {
65    frontswap_failed_stores++;
66}
67static inline void inc_frontswap_invalidates(void) {
68    frontswap_invalidates++;
69}
70#else
71static inline void inc_frontswap_loads(void) { }
72static inline void inc_frontswap_succ_stores(void) { }
73static inline void inc_frontswap_failed_stores(void) { }
74static inline void inc_frontswap_invalidates(void) { }
75#endif
76/*
77 * Register operations for frontswap, returning previous thus allowing
78 * detection of multiple backends and possible nesting.
79 */
80struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
81{
82    struct frontswap_ops old = frontswap_ops;
83
84    frontswap_ops = *ops;
85    frontswap_enabled = true;
86    return old;
87}
88EXPORT_SYMBOL(frontswap_register_ops);
89
90/*
91 * Enable/disable frontswap writethrough (see above).
92 */
93void frontswap_writethrough(bool enable)
94{
95    frontswap_writethrough_enabled = enable;
96}
97EXPORT_SYMBOL(frontswap_writethrough);
98
99/*
100 * Called when a swap device is swapon'd.
101 */
102void __frontswap_init(unsigned type)
103{
104    struct swap_info_struct *sis = swap_info[type];
105
106    BUG_ON(sis == NULL);
107    if (sis->frontswap_map == NULL)
108        return;
109    frontswap_ops.init(type);
110}
111EXPORT_SYMBOL(__frontswap_init);
112
113static inline void __frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
114{
115    frontswap_clear(sis, offset);
116    atomic_dec(&sis->frontswap_pages);
117}
118
119/*
120 * "Store" data from a page to frontswap and associate it with the page's
121 * swaptype and offset. Page must be locked and in the swap cache.
122 * If frontswap already contains a page with matching swaptype and
123 * offset, the frontswap implementation may either overwrite the data and
124 * return success or invalidate the page from frontswap and return failure.
125 */
126int __frontswap_store(struct page *page)
127{
128    int ret = -1, dup = 0;
129    swp_entry_t entry = { .val = page_private(page), };
130    int type = swp_type(entry);
131    struct swap_info_struct *sis = swap_info[type];
132    pgoff_t offset = swp_offset(entry);
133
134    BUG_ON(!PageLocked(page));
135    BUG_ON(sis == NULL);
136    if (frontswap_test(sis, offset))
137        dup = 1;
138    ret = frontswap_ops.store(type, offset, page);
139    if (ret == 0) {
140        frontswap_set(sis, offset);
141        inc_frontswap_succ_stores();
142        if (!dup)
143            atomic_inc(&sis->frontswap_pages);
144    } else {
145        /*
146          failed dup always results in automatic invalidate of
147          the (older) page from frontswap
148         */
149        inc_frontswap_failed_stores();
150        if (dup)
151            __frontswap_clear(sis, offset);
152    }
153    if (frontswap_writethrough_enabled)
154        /* report failure so swap also writes to swap device */
155        ret = -1;
156    return ret;
157}
158EXPORT_SYMBOL(__frontswap_store);
159
160/*
161 * "Get" data from frontswap associated with swaptype and offset that were
162 * specified when the data was put to frontswap and use it to fill the
163 * specified page with data. Page must be locked and in the swap cache.
164 */
165int __frontswap_load(struct page *page)
166{
167    int ret = -1;
168    swp_entry_t entry = { .val = page_private(page), };
169    int type = swp_type(entry);
170    struct swap_info_struct *sis = swap_info[type];
171    pgoff_t offset = swp_offset(entry);
172
173    BUG_ON(!PageLocked(page));
174    BUG_ON(sis == NULL);
175    if (frontswap_test(sis, offset))
176        ret = frontswap_ops.load(type, offset, page);
177    if (ret == 0)
178        inc_frontswap_loads();
179    return ret;
180}
181EXPORT_SYMBOL(__frontswap_load);
182
183/*
184 * Invalidate any data from frontswap associated with the specified swaptype
185 * and offset so that a subsequent "get" will fail.
186 */
187void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
188{
189    struct swap_info_struct *sis = swap_info[type];
190
191    BUG_ON(sis == NULL);
192    if (frontswap_test(sis, offset)) {
193        frontswap_ops.invalidate_page(type, offset);
194        __frontswap_clear(sis, offset);
195        inc_frontswap_invalidates();
196    }
197}
198EXPORT_SYMBOL(__frontswap_invalidate_page);
199
200/*
201 * Invalidate all data from frontswap associated with all offsets for the
202 * specified swaptype.
203 */
204void __frontswap_invalidate_area(unsigned type)
205{
206    struct swap_info_struct *sis = swap_info[type];
207
208    BUG_ON(sis == NULL);
209    if (sis->frontswap_map == NULL)
210        return;
211    frontswap_ops.invalidate_area(type);
212    atomic_set(&sis->frontswap_pages, 0);
213    memset(sis->frontswap_map, 0, sis->max / sizeof(long));
214}
215EXPORT_SYMBOL(__frontswap_invalidate_area);
216
217static unsigned long __frontswap_curr_pages(void)
218{
219    int type;
220    unsigned long totalpages = 0;
221    struct swap_info_struct *si = NULL;
222
223    assert_spin_locked(&swap_lock);
224    for (type = swap_list.head; type >= 0; type = si->next) {
225        si = swap_info[type];
226        totalpages += atomic_read(&si->frontswap_pages);
227    }
228    return totalpages;
229}
230
231static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
232                    int *swapid)
233{
234    int ret = -EINVAL;
235    struct swap_info_struct *si = NULL;
236    int si_frontswap_pages;
237    unsigned long total_pages_to_unuse = total;
238    unsigned long pages = 0, pages_to_unuse = 0;
239    int type;
240
241    assert_spin_locked(&swap_lock);
242    for (type = swap_list.head; type >= 0; type = si->next) {
243        si = swap_info[type];
244        si_frontswap_pages = atomic_read(&si->frontswap_pages);
245        if (total_pages_to_unuse < si_frontswap_pages) {
246            pages = pages_to_unuse = total_pages_to_unuse;
247        } else {
248            pages = si_frontswap_pages;
249            pages_to_unuse = 0; /* unuse all */
250        }
251        /* ensure there is enough RAM to fetch pages from frontswap */
252        if (security_vm_enough_memory_mm(current->mm, pages)) {
253            ret = -ENOMEM;
254            continue;
255        }
256        vm_unacct_memory(pages);
257        *unused = pages_to_unuse;
258        *swapid = type;
259        ret = 0;
260        break;
261    }
262
263    return ret;
264}
265
266static int __frontswap_shrink(unsigned long target_pages,
267                unsigned long *pages_to_unuse,
268                int *type)
269{
270    unsigned long total_pages = 0, total_pages_to_unuse;
271
272    assert_spin_locked(&swap_lock);
273
274    total_pages = __frontswap_curr_pages();
275    if (total_pages <= target_pages) {
276        /* Nothing to do */
277        *pages_to_unuse = 0;
278        return 0;
279    }
280    total_pages_to_unuse = total_pages - target_pages;
281    return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
282}
283
284/*
285 * Frontswap, like a true swap device, may unnecessarily retain pages
286 * under certain circumstances; "shrink" frontswap is essentially a
287 * "partial swapoff" and works by calling try_to_unuse to attempt to
288 * unuse enough frontswap pages to attempt to -- subject to memory
289 * constraints -- reduce the number of pages in frontswap to the
290 * number given in the parameter target_pages.
291 */
292void frontswap_shrink(unsigned long target_pages)
293{
294    unsigned long pages_to_unuse = 0;
295    int type, ret;
296
297    /*
298     * we don't want to hold swap_lock while doing a very
299     * lengthy try_to_unuse, but swap_list may change
300     * so restart scan from swap_list.head each time
301     */
302    spin_lock(&swap_lock);
303    ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
304    spin_unlock(&swap_lock);
305    if (ret == 0 && pages_to_unuse)
306        try_to_unuse(type, true, pages_to_unuse);
307    return;
308}
309EXPORT_SYMBOL(frontswap_shrink);
310
311/*
312 * Count and return the number of frontswap pages across all
313 * swap devices. This is exported so that backend drivers can
314 * determine current usage without reading debugfs.
315 */
316unsigned long frontswap_curr_pages(void)
317{
318    unsigned long totalpages = 0;
319
320    spin_lock(&swap_lock);
321    totalpages = __frontswap_curr_pages();
322    spin_unlock(&swap_lock);
323
324    return totalpages;
325}
326EXPORT_SYMBOL(frontswap_curr_pages);
327
328static int __init init_frontswap(void)
329{
330#ifdef CONFIG_DEBUG_FS
331    struct dentry *root = debugfs_create_dir("frontswap", NULL);
332    if (root == NULL)
333        return -ENXIO;
334    debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
335    debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
336    debugfs_create_u64("failed_stores", S_IRUGO, root,
337                &frontswap_failed_stores);
338    debugfs_create_u64("invalidates", S_IRUGO,
339                root, &frontswap_invalidates);
340#endif
341    return 0;
342}
343
344module_init(init_frontswap);
345

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