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 * If enabled, frontswap_store will return failure even on success. As
31 * a result, the swap subsystem will always write the page to swap, in
32 * effect converting frontswap into a writethrough cache. In this mode,
33 * there is no direct reduction in swap writes, but a frontswap backend
34 * can unilaterally "reclaim" any pages in use with no data loss, thus
35 * providing increases control over maximum memory usage due to frontswap.
36 */
37static bool frontswap_writethrough_enabled __read_mostly;
38
39/*
40 * If enabled, the underlying tmem implementation is capable of doing
41 * exclusive gets, so frontswap_load, on a successful tmem_get must
42 * mark the page as no longer in frontswap AND mark it dirty.
43 */
44static bool frontswap_tmem_exclusive_gets_enabled __read_mostly;
45
46#ifdef CONFIG_DEBUG_FS
47/*
48 * Counters available via /sys/kernel/debug/frontswap (if debugfs is
49 * properly configured). These are for information only so are not protected
50 * against increment races.
51 */
52static u64 frontswap_loads;
53static u64 frontswap_succ_stores;
54static u64 frontswap_failed_stores;
55static u64 frontswap_invalidates;
56
57static inline void inc_frontswap_loads(void) {
58    frontswap_loads++;
59}
60static inline void inc_frontswap_succ_stores(void) {
61    frontswap_succ_stores++;
62}
63static inline void inc_frontswap_failed_stores(void) {
64    frontswap_failed_stores++;
65}
66static inline void inc_frontswap_invalidates(void) {
67    frontswap_invalidates++;
68}
69#else
70static inline void inc_frontswap_loads(void) { }
71static inline void inc_frontswap_succ_stores(void) { }
72static inline void inc_frontswap_failed_stores(void) { }
73static inline void inc_frontswap_invalidates(void) { }
74#endif
75
76/*
77 * Due to the asynchronous nature of the backends loading potentially
78 * _after_ the swap system has been activated, we have chokepoints
79 * on all frontswap functions to not call the backend until the backend
80 * has registered.
81 *
82 * Specifically when no backend is registered (nobody called
83 * frontswap_register_ops) all calls to frontswap_init (which is done via
84 * swapon -> enable_swap_info -> frontswap_init) are registered and remembered
85 * (via the setting of need_init bitmap) but fail to create tmem_pools. When a
86 * backend registers with frontswap at some later point the previous
87 * calls to frontswap_init are executed (by iterating over the need_init
88 * bitmap) to create tmem_pools and set the respective poolids. All of that is
89 * guarded by us using atomic bit operations on the 'need_init' bitmap.
90 *
91 * This would not guards us against the user deciding to call swapoff right as
92 * we are calling the backend to initialize (so swapon is in action).
93 * Fortunatly for us, the swapon_mutex has been taked by the callee so we are
94 * OK. The other scenario where calls to frontswap_store (called via
95 * swap_writepage) is racing with frontswap_invalidate_area (called via
96 * swapoff) is again guarded by the swap subsystem.
97 *
98 * While no backend is registered all calls to frontswap_[store|load|
99 * invalidate_area|invalidate_page] are ignored or fail.
100 *
101 * The time between the backend being registered and the swap file system
102 * calling the backend (via the frontswap_* functions) is indeterminate as
103 * frontswap_ops is not atomic_t (or a value guarded by a spinlock).
104 * That is OK as we are comfortable missing some of these calls to the newly
105 * registered backend.
106 *
107 * Obviously the opposite (unloading the backend) must be done after all
108 * the frontswap_[store|load|invalidate_area|invalidate_page] start
109 * ignorning or failing the requests - at which point frontswap_ops
110 * would have to be made in some fashion atomic.
111 */
112static DECLARE_BITMAP(need_init, MAX_SWAPFILES);
113
114/*
115 * Register operations for frontswap, returning previous thus allowing
116 * detection of multiple backends and possible nesting.
117 */
118struct frontswap_ops *frontswap_register_ops(struct frontswap_ops *ops)
119{
120    struct frontswap_ops *old = frontswap_ops;
121    int i;
122
123    for (i = 0; i < MAX_SWAPFILES; i++) {
124        if (test_and_clear_bit(i, need_init)) {
125            struct swap_info_struct *sis = swap_info[i];
126            /* __frontswap_init _should_ have set it! */
127            if (!sis->frontswap_map)
128                return ERR_PTR(-EINVAL);
129            ops->init(i);
130        }
131    }
132    /*
133     * We MUST have frontswap_ops set _after_ the frontswap_init's
134     * have been called. Otherwise __frontswap_store might fail. Hence
135     * the barrier to make sure compiler does not re-order us.
136     */
137    barrier();
138    frontswap_ops = ops;
139    return old;
140}
141EXPORT_SYMBOL(frontswap_register_ops);
142
143/*
144 * Enable/disable frontswap writethrough (see above).
145 */
146void frontswap_writethrough(bool enable)
147{
148    frontswap_writethrough_enabled = enable;
149}
150EXPORT_SYMBOL(frontswap_writethrough);
151
152/*
153 * Enable/disable frontswap exclusive gets (see above).
154 */
155void frontswap_tmem_exclusive_gets(bool enable)
156{
157    frontswap_tmem_exclusive_gets_enabled = enable;
158}
159EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);
160
161/*
162 * Called when a swap device is swapon'd.
163 */
164void __frontswap_init(unsigned type, unsigned long *map)
165{
166    struct swap_info_struct *sis = swap_info[type];
167
168    BUG_ON(sis == NULL);
169
170    /*
171     * p->frontswap is a bitmap that we MUST have to figure out which page
172     * has gone in frontswap. Without it there is no point of continuing.
173     */
174    if (WARN_ON(!map))
175        return;
176    /*
177     * Irregardless of whether the frontswap backend has been loaded
178     * before this function or it will be later, we _MUST_ have the
179     * p->frontswap set to something valid to work properly.
180     */
181    frontswap_map_set(sis, map);
182    if (frontswap_ops)
183        frontswap_ops->init(type);
184    else {
185        BUG_ON(type > MAX_SWAPFILES);
186        set_bit(type, need_init);
187    }
188}
189EXPORT_SYMBOL(__frontswap_init);
190
191bool __frontswap_test(struct swap_info_struct *sis,
192                pgoff_t offset)
193{
194    bool ret = false;
195
196    if (frontswap_ops && sis->frontswap_map)
197        ret = test_bit(offset, sis->frontswap_map);
198    return ret;
199}
200EXPORT_SYMBOL(__frontswap_test);
201
202static inline void __frontswap_clear(struct swap_info_struct *sis,
203                pgoff_t offset)
204{
205    clear_bit(offset, sis->frontswap_map);
206    atomic_dec(&sis->frontswap_pages);
207}
208
209/*
210 * "Store" data from a page to frontswap and associate it with the page's
211 * swaptype and offset. Page must be locked and in the swap cache.
212 * If frontswap already contains a page with matching swaptype and
213 * offset, the frontswap implementation may either overwrite the data and
214 * return success or invalidate the page from frontswap and return failure.
215 */
216int __frontswap_store(struct page *page)
217{
218    int ret = -1, dup = 0;
219    swp_entry_t entry = { .val = page_private(page), };
220    int type = swp_type(entry);
221    struct swap_info_struct *sis = swap_info[type];
222    pgoff_t offset = swp_offset(entry);
223
224    /*
225     * Return if no backend registed.
226     * Don't need to inc frontswap_failed_stores here.
227     */
228    if (!frontswap_ops)
229        return ret;
230
231    BUG_ON(!PageLocked(page));
232    BUG_ON(sis == NULL);
233    if (__frontswap_test(sis, offset))
234        dup = 1;
235    ret = frontswap_ops->store(type, offset, page);
236    if (ret == 0) {
237        set_bit(offset, sis->frontswap_map);
238        inc_frontswap_succ_stores();
239        if (!dup)
240            atomic_inc(&sis->frontswap_pages);
241    } else {
242        /*
243          failed dup always results in automatic invalidate of
244          the (older) page from frontswap
245         */
246        inc_frontswap_failed_stores();
247        if (dup)
248            __frontswap_clear(sis, offset);
249    }
250    if (frontswap_writethrough_enabled)
251        /* report failure so swap also writes to swap device */
252        ret = -1;
253    return ret;
254}
255EXPORT_SYMBOL(__frontswap_store);
256
257/*
258 * "Get" data from frontswap associated with swaptype and offset that were
259 * specified when the data was put to frontswap and use it to fill the
260 * specified page with data. Page must be locked and in the swap cache.
261 */
262int __frontswap_load(struct page *page)
263{
264    int ret = -1;
265    swp_entry_t entry = { .val = page_private(page), };
266    int type = swp_type(entry);
267    struct swap_info_struct *sis = swap_info[type];
268    pgoff_t offset = swp_offset(entry);
269
270    BUG_ON(!PageLocked(page));
271    BUG_ON(sis == NULL);
272    /*
273     * __frontswap_test() will check whether there is backend registered
274     */
275    if (__frontswap_test(sis, offset))
276        ret = frontswap_ops->load(type, offset, page);
277    if (ret == 0) {
278        inc_frontswap_loads();
279        if (frontswap_tmem_exclusive_gets_enabled) {
280            SetPageDirty(page);
281            __frontswap_clear(sis, offset);
282        }
283    }
284    return ret;
285}
286EXPORT_SYMBOL(__frontswap_load);
287
288/*
289 * Invalidate any data from frontswap associated with the specified swaptype
290 * and offset so that a subsequent "get" will fail.
291 */
292void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
293{
294    struct swap_info_struct *sis = swap_info[type];
295
296    BUG_ON(sis == NULL);
297    /*
298     * __frontswap_test() will check whether there is backend registered
299     */
300    if (__frontswap_test(sis, offset)) {
301        frontswap_ops->invalidate_page(type, offset);
302        __frontswap_clear(sis, offset);
303        inc_frontswap_invalidates();
304    }
305}
306EXPORT_SYMBOL(__frontswap_invalidate_page);
307
308/*
309 * Invalidate all data from frontswap associated with all offsets for the
310 * specified swaptype.
311 */
312void __frontswap_invalidate_area(unsigned type)
313{
314    struct swap_info_struct *sis = swap_info[type];
315
316    if (frontswap_ops) {
317        BUG_ON(sis == NULL);
318        if (sis->frontswap_map == NULL)
319            return;
320        frontswap_ops->invalidate_area(type);
321        atomic_set(&sis->frontswap_pages, 0);
322        bitmap_zero(sis->frontswap_map, sis->max);
323    }
324    clear_bit(type, need_init);
325}
326EXPORT_SYMBOL(__frontswap_invalidate_area);
327
328static unsigned long __frontswap_curr_pages(void)
329{
330    int type;
331    unsigned long totalpages = 0;
332    struct swap_info_struct *si = NULL;
333
334    assert_spin_locked(&swap_lock);
335    for (type = swap_list.head; type >= 0; type = si->next) {
336        si = swap_info[type];
337        totalpages += atomic_read(&si->frontswap_pages);
338    }
339    return totalpages;
340}
341
342static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
343                    int *swapid)
344{
345    int ret = -EINVAL;
346    struct swap_info_struct *si = NULL;
347    int si_frontswap_pages;
348    unsigned long total_pages_to_unuse = total;
349    unsigned long pages = 0, pages_to_unuse = 0;
350    int type;
351
352    assert_spin_locked(&swap_lock);
353    for (type = swap_list.head; type >= 0; type = si->next) {
354        si = swap_info[type];
355        si_frontswap_pages = atomic_read(&si->frontswap_pages);
356        if (total_pages_to_unuse < si_frontswap_pages) {
357            pages = pages_to_unuse = total_pages_to_unuse;
358        } else {
359            pages = si_frontswap_pages;
360            pages_to_unuse = 0; /* unuse all */
361        }
362        /* ensure there is enough RAM to fetch pages from frontswap */
363        if (security_vm_enough_memory_mm(current->mm, pages)) {
364            ret = -ENOMEM;
365            continue;
366        }
367        vm_unacct_memory(pages);
368        *unused = pages_to_unuse;
369        *swapid = type;
370        ret = 0;
371        break;
372    }
373
374    return ret;
375}
376
377/*
378 * Used to check if it's necessory and feasible to unuse pages.
379 * Return 1 when nothing to do, 0 when need to shink pages,
380 * error code when there is an error.
381 */
382static int __frontswap_shrink(unsigned long target_pages,
383                unsigned long *pages_to_unuse,
384                int *type)
385{
386    unsigned long total_pages = 0, total_pages_to_unuse;
387
388    assert_spin_locked(&swap_lock);
389
390    total_pages = __frontswap_curr_pages();
391    if (total_pages <= target_pages) {
392        /* Nothing to do */
393        *pages_to_unuse = 0;
394        return 1;
395    }
396    total_pages_to_unuse = total_pages - target_pages;
397    return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
398}
399
400/*
401 * Frontswap, like a true swap device, may unnecessarily retain pages
402 * under certain circumstances; "shrink" frontswap is essentially a
403 * "partial swapoff" and works by calling try_to_unuse to attempt to
404 * unuse enough frontswap pages to attempt to -- subject to memory
405 * constraints -- reduce the number of pages in frontswap to the
406 * number given in the parameter target_pages.
407 */
408void frontswap_shrink(unsigned long target_pages)
409{
410    unsigned long pages_to_unuse = 0;
411    int uninitialized_var(type), ret;
412
413    /*
414     * we don't want to hold swap_lock while doing a very
415     * lengthy try_to_unuse, but swap_list may change
416     * so restart scan from swap_list.head each time
417     */
418    spin_lock(&swap_lock);
419    ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
420    spin_unlock(&swap_lock);
421    if (ret == 0)
422        try_to_unuse(type, true, pages_to_unuse);
423    return;
424}
425EXPORT_SYMBOL(frontswap_shrink);
426
427/*
428 * Count and return the number of frontswap pages across all
429 * swap devices. This is exported so that backend drivers can
430 * determine current usage without reading debugfs.
431 */
432unsigned long frontswap_curr_pages(void)
433{
434    unsigned long totalpages = 0;
435
436    spin_lock(&swap_lock);
437    totalpages = __frontswap_curr_pages();
438    spin_unlock(&swap_lock);
439
440    return totalpages;
441}
442EXPORT_SYMBOL(frontswap_curr_pages);
443
444static int __init init_frontswap(void)
445{
446#ifdef CONFIG_DEBUG_FS
447    struct dentry *root = debugfs_create_dir("frontswap", NULL);
448    if (root == NULL)
449        return -ENXIO;
450    debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
451    debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
452    debugfs_create_u64("failed_stores", S_IRUGO, root,
453                &frontswap_failed_stores);
454    debugfs_create_u64("invalidates", S_IRUGO,
455                root, &frontswap_invalidates);
456#endif
457    return 0;
458}
459
460module_init(init_frontswap);
461

Archive Download this file

Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master

Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9



interactive