blob: 8a529a01e8fc79ebda8cfe30191fa9fb1d754b77 [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * linux/mm/swap.c
3 *
4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
5 */
6
7/*
Simon Arlott183ff222007-10-20 01:27:18 +02008 * This file contains the default values for the operation of the
Linus Torvalds1da177e2005-04-16 15:20:36 -07009 * Linux VM subsystem. Fine-tuning documentation can be found in
10 * Documentation/sysctl/vm.txt.
11 * Started 18.12.91
12 * Swap aging added 23.2.95, Stephen Tweedie.
13 * Buffermem limits added 12.3.98, Rik van Riel.
14 */
15
16#include <linux/mm.h>
17#include <linux/sched.h>
18#include <linux/kernel_stat.h>
19#include <linux/swap.h>
20#include <linux/mman.h>
21#include <linux/pagemap.h>
22#include <linux/pagevec.h>
23#include <linux/init.h>
Paul Gortmakerb95f1b312011-10-16 02:01:52 -040024#include <linux/export.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070025#include <linux/mm_inline.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070026#include <linux/percpu_counter.h>
27#include <linux/percpu.h>
28#include <linux/cpu.h>
29#include <linux/notifier.h>
Peter Zijlstrae0bf68d2007-10-16 23:25:46 -070030#include <linux/backing-dev.h>
Balbir Singh66e17072008-02-07 00:13:56 -080031#include <linux/memcontrol.h>
Tejun Heo5a0e3ad2010-03-24 17:04:11 +090032#include <linux/gfp.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070033
Lee Schermerhorn64d65192008-10-18 20:26:52 -070034#include "internal.h"
35
Linus Torvalds1da177e2005-04-16 15:20:36 -070036/* How many pages do we try to swap or page in/out together? */
37int page_cluster;
38
KOSAKI Motohirof04e9eb2008-10-18 20:26:19 -070039static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
Vegard Nossumf84f95042008-07-23 21:28:14 -070040static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
Minchan Kim31560182011-03-22 16:32:52 -070041static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
Hisashi Hifumi902aaed2007-10-16 01:24:52 -070042
Adrian Bunkb2213852006-09-25 23:31:02 -070043/*
44 * This path almost never happens for VM activity - pages are normally
45 * freed via pagevecs. But it gets used by networking.
46 */
Harvey Harrison920c7a52008-02-04 22:29:26 -080047static void __page_cache_release(struct page *page)
Adrian Bunkb2213852006-09-25 23:31:02 -070048{
49 if (PageLRU(page)) {
Adrian Bunkb2213852006-09-25 23:31:02 -070050 struct zone *zone = page_zone(page);
Hugh Dickinsfa9add62012-05-29 15:07:09 -070051 struct lruvec *lruvec;
52 unsigned long flags;
Adrian Bunkb2213852006-09-25 23:31:02 -070053
54 spin_lock_irqsave(&zone->lru_lock, flags);
Hugh Dickinsfa9add62012-05-29 15:07:09 -070055 lruvec = mem_cgroup_page_lruvec(page, zone);
Adrian Bunkb2213852006-09-25 23:31:02 -070056 VM_BUG_ON(!PageLRU(page));
57 __ClearPageLRU(page);
Hugh Dickinsfa9add62012-05-29 15:07:09 -070058 del_page_from_lru_list(page, lruvec, page_off_lru(page));
Adrian Bunkb2213852006-09-25 23:31:02 -070059 spin_unlock_irqrestore(&zone->lru_lock, flags);
60 }
Andrea Arcangeli91807062011-01-13 15:46:32 -080061}
62
63static void __put_single_page(struct page *page)
64{
65 __page_cache_release(page);
Li Hongfc916682010-03-05 13:41:54 -080066 free_hot_cold_page(page, 0);
Adrian Bunkb2213852006-09-25 23:31:02 -070067}
68
Andrea Arcangeli91807062011-01-13 15:46:32 -080069static void __put_compound_page(struct page *page)
70{
71 compound_page_dtor *dtor;
72
73 __page_cache_release(page);
74 dtor = get_compound_page_dtor(page);
75 (*dtor)(page);
76}
77
Nick Piggin8519fb32006-02-07 12:58:52 -080078static void put_compound_page(struct page *page)
79{
Andrea Arcangeli91807062011-01-13 15:46:32 -080080 if (unlikely(PageTail(page))) {
81 /* __split_huge_page_refcount can run under us */
Andrea Arcangeli70b50f92011-11-02 13:36:59 -070082 struct page *page_head = compound_trans_head(page);
83
84 if (likely(page != page_head &&
85 get_page_unless_zero(page_head))) {
Andrea Arcangeli91807062011-01-13 15:46:32 -080086 unsigned long flags;
Pravin B Shelar5bf5f032012-05-29 15:06:49 -070087
88 /*
89 * THP can not break up slab pages so avoid taking
90 * compound_lock(). Slab performs non-atomic bit ops
91 * on page->flags for better performance. In particular
92 * slab_unlock() in slub used to be a hot path. It is
93 * still hot on arches that do not support
94 * this_cpu_cmpxchg_double().
95 */
96 if (PageSlab(page_head)) {
97 if (PageTail(page)) {
98 if (put_page_testzero(page_head))
99 VM_BUG_ON(1);
100
101 atomic_dec(&page->_mapcount);
102 goto skip_lock_tail;
103 } else
104 goto skip_lock;
105 }
Andrea Arcangeli91807062011-01-13 15:46:32 -0800106 /*
Andrea Arcangeli70b50f92011-11-02 13:36:59 -0700107 * page_head wasn't a dangling pointer but it
108 * may not be a head page anymore by the time
109 * we obtain the lock. That is ok as long as it
110 * can't be freed from under us.
Andrea Arcangeli91807062011-01-13 15:46:32 -0800111 */
Andrea Arcangeli91807062011-01-13 15:46:32 -0800112 flags = compound_lock_irqsave(page_head);
113 if (unlikely(!PageTail(page))) {
114 /* __split_huge_page_refcount run before us */
115 compound_unlock_irqrestore(page_head, flags);
Pravin B Shelar5bf5f032012-05-29 15:06:49 -0700116skip_lock:
Andrea Arcangeli91807062011-01-13 15:46:32 -0800117 if (put_page_testzero(page_head))
118 __put_single_page(page_head);
Pravin B Shelar5bf5f032012-05-29 15:06:49 -0700119out_put_single:
Andrea Arcangeli91807062011-01-13 15:46:32 -0800120 if (put_page_testzero(page))
121 __put_single_page(page);
122 return;
123 }
124 VM_BUG_ON(page_head != page->first_page);
125 /*
126 * We can release the refcount taken by
Andrea Arcangeli70b50f92011-11-02 13:36:59 -0700127 * get_page_unless_zero() now that
128 * __split_huge_page_refcount() is blocked on
129 * the compound_lock.
Andrea Arcangeli91807062011-01-13 15:46:32 -0800130 */
131 if (put_page_testzero(page_head))
132 VM_BUG_ON(1);
133 /* __split_huge_page_refcount will wait now */
Andrea Arcangeli70b50f92011-11-02 13:36:59 -0700134 VM_BUG_ON(page_mapcount(page) <= 0);
135 atomic_dec(&page->_mapcount);
Andrea Arcangeli91807062011-01-13 15:46:32 -0800136 VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
Andrea Arcangeli70b50f92011-11-02 13:36:59 -0700137 VM_BUG_ON(atomic_read(&page->_count) != 0);
Andrea Arcangeli91807062011-01-13 15:46:32 -0800138 compound_unlock_irqrestore(page_head, flags);
Pravin B Shelar5bf5f032012-05-29 15:06:49 -0700139
140skip_lock_tail:
Andrea Arcangelia95a82e2011-01-13 15:46:33 -0800141 if (put_page_testzero(page_head)) {
142 if (PageHead(page_head))
143 __put_compound_page(page_head);
144 else
145 __put_single_page(page_head);
146 }
Andrea Arcangeli91807062011-01-13 15:46:32 -0800147 } else {
148 /* page_head is a dangling pointer */
149 VM_BUG_ON(PageTail(page));
150 goto out_put_single;
151 }
152 } else if (put_page_testzero(page)) {
153 if (PageHead(page))
154 __put_compound_page(page);
155 else
156 __put_single_page(page);
Nick Piggin8519fb32006-02-07 12:58:52 -0800157 }
158}
159
Linus Torvalds1da177e2005-04-16 15:20:36 -0700160void put_page(struct page *page)
161{
Nick Piggin8519fb32006-02-07 12:58:52 -0800162 if (unlikely(PageCompound(page)))
163 put_compound_page(page);
164 else if (put_page_testzero(page))
Andrea Arcangeli91807062011-01-13 15:46:32 -0800165 __put_single_page(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700166}
167EXPORT_SYMBOL(put_page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700168
Andrea Arcangeli70b50f92011-11-02 13:36:59 -0700169/*
170 * This function is exported but must not be called by anything other
171 * than get_page(). It implements the slow path of get_page().
172 */
173bool __get_page_tail(struct page *page)
174{
175 /*
176 * This takes care of get_page() if run on a tail page
177 * returned by one of the get_user_pages/follow_page variants.
178 * get_user_pages/follow_page itself doesn't need the compound
179 * lock because it runs __get_page_tail_foll() under the
180 * proper PT lock that already serializes against
181 * split_huge_page().
182 */
183 unsigned long flags;
184 bool got = false;
185 struct page *page_head = compound_trans_head(page);
186
187 if (likely(page != page_head && get_page_unless_zero(page_head))) {
Pravin B Shelar5bf5f032012-05-29 15:06:49 -0700188
189 /* Ref to put_compound_page() comment. */
190 if (PageSlab(page_head)) {
191 if (likely(PageTail(page))) {
192 __get_page_tail_foll(page, false);
193 return true;
194 } else {
195 put_page(page_head);
196 return false;
197 }
198 }
199
Andrea Arcangeli70b50f92011-11-02 13:36:59 -0700200 /*
201 * page_head wasn't a dangling pointer but it
202 * may not be a head page anymore by the time
203 * we obtain the lock. That is ok as long as it
204 * can't be freed from under us.
205 */
206 flags = compound_lock_irqsave(page_head);
207 /* here __split_huge_page_refcount won't run anymore */
208 if (likely(PageTail(page))) {
209 __get_page_tail_foll(page, false);
210 got = true;
211 }
212 compound_unlock_irqrestore(page_head, flags);
213 if (unlikely(!got))
214 put_page(page_head);
215 }
216 return got;
217}
218EXPORT_SYMBOL(__get_page_tail);
219
Alexander Zarochentsev1d7ea732006-08-13 23:24:27 -0700220/**
Randy Dunlap76824862008-03-19 17:00:40 -0700221 * put_pages_list() - release a list of pages
222 * @pages: list of pages threaded on page->lru
Alexander Zarochentsev1d7ea732006-08-13 23:24:27 -0700223 *
224 * Release a list of pages which are strung together on page.lru. Currently
225 * used by read_cache_pages() and related error recovery code.
Alexander Zarochentsev1d7ea732006-08-13 23:24:27 -0700226 */
227void put_pages_list(struct list_head *pages)
228{
229 while (!list_empty(pages)) {
230 struct page *victim;
231
232 victim = list_entry(pages->prev, struct page, lru);
233 list_del(&victim->lru);
234 page_cache_release(victim);
235 }
236}
237EXPORT_SYMBOL(put_pages_list);
238
Mel Gorman18022c52012-07-31 16:44:51 -0700239/*
240 * get_kernel_pages() - pin kernel pages in memory
241 * @kiov: An array of struct kvec structures
242 * @nr_segs: number of segments to pin
243 * @write: pinning for read/write, currently ignored
244 * @pages: array that receives pointers to the pages pinned.
245 * Should be at least nr_segs long.
246 *
247 * Returns number of pages pinned. This may be fewer than the number
248 * requested. If nr_pages is 0 or negative, returns 0. If no pages
249 * were pinned, returns -errno. Each page returned must be released
250 * with a put_page() call when it is finished with.
251 */
252int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
253 struct page **pages)
254{
255 int seg;
256
257 for (seg = 0; seg < nr_segs; seg++) {
258 if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
259 return seg;
260
Mel Gorman5a178112012-07-31 16:45:02 -0700261 pages[seg] = kmap_to_page(kiov[seg].iov_base);
Mel Gorman18022c52012-07-31 16:44:51 -0700262 page_cache_get(pages[seg]);
263 }
264
265 return seg;
266}
267EXPORT_SYMBOL_GPL(get_kernel_pages);
268
269/*
270 * get_kernel_page() - pin a kernel page in memory
271 * @start: starting kernel address
272 * @write: pinning for read/write, currently ignored
273 * @pages: array that receives pointer to the page pinned.
274 * Must be at least nr_segs long.
275 *
276 * Returns 1 if page is pinned. If the page was not pinned, returns
277 * -errno. The page returned must be released with a put_page() call
278 * when it is finished with.
279 */
280int get_kernel_page(unsigned long start, int write, struct page **pages)
281{
282 const struct kvec kiov = {
283 .iov_base = (void *)start,
284 .iov_len = PAGE_SIZE
285 };
286
287 return get_kernel_pages(&kiov, 1, write, pages);
288}
289EXPORT_SYMBOL_GPL(get_kernel_page);
290
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700291static void pagevec_lru_move_fn(struct pagevec *pvec,
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700292 void (*move_fn)(struct page *page, struct lruvec *lruvec, void *arg),
293 void *arg)
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700294{
295 int i;
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700296 struct zone *zone = NULL;
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700297 struct lruvec *lruvec;
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700298 unsigned long flags = 0;
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700299
300 for (i = 0; i < pagevec_count(pvec); i++) {
301 struct page *page = pvec->pages[i];
302 struct zone *pagezone = page_zone(page);
303
304 if (pagezone != zone) {
305 if (zone)
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700306 spin_unlock_irqrestore(&zone->lru_lock, flags);
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700307 zone = pagezone;
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700308 spin_lock_irqsave(&zone->lru_lock, flags);
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700309 }
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700310
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700311 lruvec = mem_cgroup_page_lruvec(page, zone);
312 (*move_fn)(page, lruvec, arg);
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700313 }
314 if (zone)
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700315 spin_unlock_irqrestore(&zone->lru_lock, flags);
Linus Torvalds83896fb2011-01-17 14:42:34 -0800316 release_pages(pvec->pages, pvec->nr, pvec->cold);
317 pagevec_reinit(pvec);
Shaohua Lid8505de2011-01-13 15:47:33 -0800318}
319
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700320static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec,
321 void *arg)
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700322{
323 int *pgmoved = arg;
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700324
325 if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
326 enum lru_list lru = page_lru_base_type(page);
Johannes Weiner925b7672012-01-12 17:18:15 -0800327 list_move_tail(&page->lru, &lruvec->lists[lru]);
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700328 (*pgmoved)++;
329 }
330}
331
332/*
333 * pagevec_move_tail() must be called with IRQ disabled.
334 * Otherwise this may cause nasty races.
335 */
336static void pagevec_move_tail(struct pagevec *pvec)
337{
338 int pgmoved = 0;
339
340 pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved);
341 __count_vm_events(PGROTATED, pgmoved);
342}
343
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700344/*
Linus Torvalds1da177e2005-04-16 15:20:36 -0700345 * Writeback is about to end against a page which has been marked for immediate
346 * reclaim. If it still appears to be reclaimable, move it to the tail of the
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700347 * inactive list.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700348 */
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700349void rotate_reclaimable_page(struct page *page)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700350{
Miklos Szerediac6aadb2008-04-28 02:12:38 -0700351 if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) &&
Lee Schermerhorn894bc312008-10-18 20:26:39 -0700352 !PageUnevictable(page) && PageLRU(page)) {
Miklos Szerediac6aadb2008-04-28 02:12:38 -0700353 struct pagevec *pvec;
354 unsigned long flags;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700355
Miklos Szerediac6aadb2008-04-28 02:12:38 -0700356 page_cache_get(page);
357 local_irq_save(flags);
358 pvec = &__get_cpu_var(lru_rotate_pvecs);
359 if (!pagevec_add(pvec, page))
360 pagevec_move_tail(pvec);
361 local_irq_restore(flags);
362 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700363}
364
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700365static void update_page_reclaim_stat(struct lruvec *lruvec,
KOSAKI Motohiro3e2f41f2009-01-07 18:08:20 -0800366 int file, int rotated)
367{
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700368 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
KOSAKI Motohiro3e2f41f2009-01-07 18:08:20 -0800369
370 reclaim_stat->recent_scanned[file]++;
371 if (rotated)
372 reclaim_stat->recent_rotated[file]++;
KOSAKI Motohiro3e2f41f2009-01-07 18:08:20 -0800373}
374
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700375static void __activate_page(struct page *page, struct lruvec *lruvec,
376 void *arg)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700377{
Linus Torvalds7a608572011-01-17 14:42:19 -0800378 if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
379 int file = page_is_file_cache(page);
380 int lru = page_lru_base_type(page);
Linus Torvalds7a608572011-01-17 14:42:19 -0800381
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700382 del_page_from_lru_list(page, lruvec, lru);
Linus Torvalds7a608572011-01-17 14:42:19 -0800383 SetPageActive(page);
384 lru += LRU_ACTIVE;
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700385 add_page_to_lru_list(page, lruvec, lru);
Linus Torvalds7a608572011-01-17 14:42:19 -0800386
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700387 __count_vm_event(PGACTIVATE);
388 update_page_reclaim_stat(lruvec, file, 1);
Linus Torvalds7a608572011-01-17 14:42:19 -0800389 }
Shaohua Lieb709b02011-05-24 17:12:55 -0700390}
391
392#ifdef CONFIG_SMP
393static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
394
395static void activate_page_drain(int cpu)
396{
397 struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
398
399 if (pagevec_count(pvec))
400 pagevec_lru_move_fn(pvec, __activate_page, NULL);
401}
402
403void activate_page(struct page *page)
404{
405 if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
406 struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
407
408 page_cache_get(page);
409 if (!pagevec_add(pvec, page))
410 pagevec_lru_move_fn(pvec, __activate_page, NULL);
411 put_cpu_var(activate_page_pvecs);
412 }
413}
414
415#else
416static inline void activate_page_drain(int cpu)
417{
418}
419
420void activate_page(struct page *page)
421{
422 struct zone *zone = page_zone(page);
423
424 spin_lock_irq(&zone->lru_lock);
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700425 __activate_page(page, mem_cgroup_page_lruvec(page, zone), NULL);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700426 spin_unlock_irq(&zone->lru_lock);
427}
Shaohua Lieb709b02011-05-24 17:12:55 -0700428#endif
Linus Torvalds1da177e2005-04-16 15:20:36 -0700429
430/*
431 * Mark a page as having seen activity.
432 *
433 * inactive,unreferenced -> inactive,referenced
434 * inactive,referenced -> active,unreferenced
435 * active,unreferenced -> active,referenced
436 */
Harvey Harrison920c7a52008-02-04 22:29:26 -0800437void mark_page_accessed(struct page *page)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700438{
Lee Schermerhorn894bc312008-10-18 20:26:39 -0700439 if (!PageActive(page) && !PageUnevictable(page) &&
440 PageReferenced(page) && PageLRU(page)) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700441 activate_page(page);
442 ClearPageReferenced(page);
443 } else if (!PageReferenced(page)) {
444 SetPageReferenced(page);
445 }
446}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700447EXPORT_SYMBOL(mark_page_accessed);
448
Robin Dongd741c9c2012-10-08 16:29:05 -0700449/*
450 * Order of operations is important: flush the pagevec when it's already
451 * full, not when adding the last page, to make sure that last page is
452 * not added to the LRU directly when passed to this function. Because
453 * mark_page_accessed() (called after this when writing) only activates
454 * pages that are on the LRU, linear writes in subpage chunks would see
455 * every PAGEVEC_SIZE page activated, which is unexpected.
456 */
KOSAKI Motohirof04e9eb2008-10-18 20:26:19 -0700457void __lru_cache_add(struct page *page, enum lru_list lru)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700458{
KOSAKI Motohirof04e9eb2008-10-18 20:26:19 -0700459 struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];
Linus Torvalds1da177e2005-04-16 15:20:36 -0700460
461 page_cache_get(page);
Robin Dongd741c9c2012-10-08 16:29:05 -0700462 if (!pagevec_space(pvec))
Hugh Dickins5095ae832012-01-12 17:19:58 -0800463 __pagevec_lru_add(pvec, lru);
Robin Dongd741c9c2012-10-08 16:29:05 -0700464 pagevec_add(pvec, page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700465 put_cpu_var(lru_add_pvecs);
466}
Miklos Szeredi47846b02010-05-25 15:06:06 +0200467EXPORT_SYMBOL(__lru_cache_add);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700468
KOSAKI Motohirof04e9eb2008-10-18 20:26:19 -0700469/**
470 * lru_cache_add_lru - add a page to a page list
471 * @page: the page to be added to the LRU.
472 * @lru: the LRU list to which the page is added.
473 */
474void lru_cache_add_lru(struct page *page, enum lru_list lru)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700475{
KOSAKI Motohirof04e9eb2008-10-18 20:26:19 -0700476 if (PageActive(page)) {
Lee Schermerhorn894bc312008-10-18 20:26:39 -0700477 VM_BUG_ON(PageUnevictable(page));
KOSAKI Motohirof04e9eb2008-10-18 20:26:19 -0700478 ClearPageActive(page);
Lee Schermerhorn894bc312008-10-18 20:26:39 -0700479 } else if (PageUnevictable(page)) {
480 VM_BUG_ON(PageActive(page));
481 ClearPageUnevictable(page);
KOSAKI Motohirof04e9eb2008-10-18 20:26:19 -0700482 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700483
Lee Schermerhorn894bc312008-10-18 20:26:39 -0700484 VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page));
KOSAKI Motohirof04e9eb2008-10-18 20:26:19 -0700485 __lru_cache_add(page, lru);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700486}
487
Lee Schermerhorn894bc312008-10-18 20:26:39 -0700488/**
489 * add_page_to_unevictable_list - add a page to the unevictable list
490 * @page: the page to be added to the unevictable list
491 *
492 * Add page directly to its zone's unevictable list. To avoid races with
493 * tasks that might be making the page evictable, through eg. munlock,
494 * munmap or exit, while it's not on the lru, we want to add the page
495 * while it's locked or otherwise "invisible" to other tasks. This is
496 * difficult to do when using the pagevec cache, so bypass that.
497 */
498void add_page_to_unevictable_list(struct page *page)
499{
500 struct zone *zone = page_zone(page);
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700501 struct lruvec *lruvec;
Lee Schermerhorn894bc312008-10-18 20:26:39 -0700502
503 spin_lock_irq(&zone->lru_lock);
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700504 lruvec = mem_cgroup_page_lruvec(page, zone);
Lee Schermerhorn894bc312008-10-18 20:26:39 -0700505 SetPageUnevictable(page);
506 SetPageLRU(page);
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700507 add_page_to_lru_list(page, lruvec, LRU_UNEVICTABLE);
Lee Schermerhorn894bc312008-10-18 20:26:39 -0700508 spin_unlock_irq(&zone->lru_lock);
509}
510
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700511/*
Minchan Kim31560182011-03-22 16:32:52 -0700512 * If the page can not be invalidated, it is moved to the
513 * inactive list to speed up its reclaim. It is moved to the
514 * head of the list, rather than the tail, to give the flusher
515 * threads some time to write it out, as this is much more
516 * effective than the single-page writeout from reclaim.
Minchan Kim278df9f2011-03-22 16:32:54 -0700517 *
518 * If the page isn't page_mapped and dirty/writeback, the page
519 * could reclaim asap using PG_reclaim.
520 *
521 * 1. active, mapped page -> none
522 * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
523 * 3. inactive, mapped page -> none
524 * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
525 * 5. inactive, clean -> inactive, tail
526 * 6. Others -> none
527 *
528 * In 4, why it moves inactive's head, the VM expects the page would
529 * be write it out by flusher threads as this is much more effective
530 * than the single-page writeout from reclaim.
Minchan Kim31560182011-03-22 16:32:52 -0700531 */
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700532static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
533 void *arg)
Minchan Kim31560182011-03-22 16:32:52 -0700534{
535 int lru, file;
Minchan Kim278df9f2011-03-22 16:32:54 -0700536 bool active;
Minchan Kim31560182011-03-22 16:32:52 -0700537
Minchan Kim278df9f2011-03-22 16:32:54 -0700538 if (!PageLRU(page))
Minchan Kim31560182011-03-22 16:32:52 -0700539 return;
540
Minchan Kimbad49d92011-05-11 15:13:30 -0700541 if (PageUnevictable(page))
542 return;
543
Minchan Kim31560182011-03-22 16:32:52 -0700544 /* Some processes are using the page */
545 if (page_mapped(page))
546 return;
547
Minchan Kim278df9f2011-03-22 16:32:54 -0700548 active = PageActive(page);
Minchan Kim31560182011-03-22 16:32:52 -0700549 file = page_is_file_cache(page);
550 lru = page_lru_base_type(page);
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700551
552 del_page_from_lru_list(page, lruvec, lru + active);
Minchan Kim31560182011-03-22 16:32:52 -0700553 ClearPageActive(page);
554 ClearPageReferenced(page);
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700555 add_page_to_lru_list(page, lruvec, lru);
Minchan Kim31560182011-03-22 16:32:52 -0700556
Minchan Kim278df9f2011-03-22 16:32:54 -0700557 if (PageWriteback(page) || PageDirty(page)) {
558 /*
559 * PG_reclaim could be raced with end_page_writeback
560 * It can make readahead confusing. But race window
561 * is _really_ small and it's non-critical problem.
562 */
563 SetPageReclaim(page);
564 } else {
565 /*
566 * The page's writeback ends up during pagevec
567 * We moves tha page into tail of inactive.
568 */
Johannes Weiner925b7672012-01-12 17:18:15 -0800569 list_move_tail(&page->lru, &lruvec->lists[lru]);
Minchan Kim278df9f2011-03-22 16:32:54 -0700570 __count_vm_event(PGROTATED);
571 }
572
573 if (active)
574 __count_vm_event(PGDEACTIVATE);
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700575 update_page_reclaim_stat(lruvec, file, 0);
Minchan Kim31560182011-03-22 16:32:52 -0700576}
577
Minchan Kim31560182011-03-22 16:32:52 -0700578/*
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700579 * Drain pages out of the cpu's pagevecs.
580 * Either "cpu" is the current CPU, and preemption has already been
581 * disabled; or "cpu" is being hot-unplugged, and is already dead.
582 */
Konstantin Khlebnikovf0cb3c72012-03-21 16:34:06 -0700583void lru_add_drain_cpu(int cpu)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700584{
KOSAKI Motohirof04e9eb2008-10-18 20:26:19 -0700585 struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700586 struct pagevec *pvec;
KOSAKI Motohirof04e9eb2008-10-18 20:26:19 -0700587 int lru;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700588
KOSAKI Motohirof04e9eb2008-10-18 20:26:19 -0700589 for_each_lru(lru) {
590 pvec = &pvecs[lru - LRU_BASE];
591 if (pagevec_count(pvec))
Hugh Dickins5095ae832012-01-12 17:19:58 -0800592 __pagevec_lru_add(pvec, lru);
KOSAKI Motohirof04e9eb2008-10-18 20:26:19 -0700593 }
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700594
595 pvec = &per_cpu(lru_rotate_pvecs, cpu);
596 if (pagevec_count(pvec)) {
597 unsigned long flags;
598
599 /* No harm done if a racing interrupt already did this */
600 local_irq_save(flags);
601 pagevec_move_tail(pvec);
602 local_irq_restore(flags);
603 }
Minchan Kim31560182011-03-22 16:32:52 -0700604
605 pvec = &per_cpu(lru_deactivate_pvecs, cpu);
606 if (pagevec_count(pvec))
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700607 pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
Shaohua Lieb709b02011-05-24 17:12:55 -0700608
609 activate_page_drain(cpu);
Minchan Kim31560182011-03-22 16:32:52 -0700610}
611
612/**
613 * deactivate_page - forcefully deactivate a page
614 * @page: page to deactivate
615 *
616 * This function hints the VM that @page is a good reclaim candidate,
617 * for example if its invalidation fails due to the page being dirty
618 * or under writeback.
619 */
620void deactivate_page(struct page *page)
621{
Minchan Kim821ed6b2011-05-24 17:12:31 -0700622 /*
623 * In a workload with many unevictable page such as mprotect, unevictable
624 * page deactivation for accelerating reclaim is pointless.
625 */
626 if (PageUnevictable(page))
627 return;
628
Minchan Kim31560182011-03-22 16:32:52 -0700629 if (likely(get_page_unless_zero(page))) {
630 struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
631
632 if (!pagevec_add(pvec, page))
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700633 pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
Minchan Kim31560182011-03-22 16:32:52 -0700634 put_cpu_var(lru_deactivate_pvecs);
635 }
Andrew Morton80bfed92006-01-06 00:11:14 -0800636}
637
638void lru_add_drain(void)
639{
Konstantin Khlebnikovf0cb3c72012-03-21 16:34:06 -0700640 lru_add_drain_cpu(get_cpu());
Andrew Morton80bfed92006-01-06 00:11:14 -0800641 put_cpu();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700642}
643
David Howellsc4028952006-11-22 14:57:56 +0000644static void lru_add_drain_per_cpu(struct work_struct *dummy)
Nick Piggin053837f2006-01-18 17:42:27 -0800645{
646 lru_add_drain();
647}
648
649/*
650 * Returns 0 for success
651 */
652int lru_add_drain_all(void)
653{
David Howellsc4028952006-11-22 14:57:56 +0000654 return schedule_on_each_cpu(lru_add_drain_per_cpu);
Nick Piggin053837f2006-01-18 17:42:27 -0800655}
656
Linus Torvalds1da177e2005-04-16 15:20:36 -0700657/*
Linus Torvalds1da177e2005-04-16 15:20:36 -0700658 * Batched page_cache_release(). Decrement the reference count on all the
659 * passed pages. If it fell to zero then remove the page from the LRU and
660 * free it.
661 *
662 * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
663 * for the remainder of the operation.
664 *
Fernando Luis Vazquez Caoab33dc02008-07-29 22:33:40 -0700665 * The locking in this function is against shrink_inactive_list(): we recheck
666 * the page count inside the lock to see whether shrink_inactive_list()
667 * grabbed the page via the LRU. If it did, give up: shrink_inactive_list()
668 * will free it.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700669 */
670void release_pages(struct page **pages, int nr, int cold)
671{
672 int i;
Konstantin Khlebnikovcc598502012-01-10 15:07:04 -0800673 LIST_HEAD(pages_to_free);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700674 struct zone *zone = NULL;
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700675 struct lruvec *lruvec;
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700676 unsigned long uninitialized_var(flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700677
Linus Torvalds1da177e2005-04-16 15:20:36 -0700678 for (i = 0; i < nr; i++) {
679 struct page *page = pages[i];
Linus Torvalds1da177e2005-04-16 15:20:36 -0700680
Nick Piggin8519fb32006-02-07 12:58:52 -0800681 if (unlikely(PageCompound(page))) {
682 if (zone) {
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700683 spin_unlock_irqrestore(&zone->lru_lock, flags);
Nick Piggin8519fb32006-02-07 12:58:52 -0800684 zone = NULL;
685 }
686 put_compound_page(page);
687 continue;
688 }
689
Nick Pigginb5810032005-10-29 18:16:12 -0700690 if (!put_page_testzero(page))
Linus Torvalds1da177e2005-04-16 15:20:36 -0700691 continue;
692
Nick Piggin46453a62006-03-22 00:07:58 -0800693 if (PageLRU(page)) {
694 struct zone *pagezone = page_zone(page);
Lee Schermerhorn894bc312008-10-18 20:26:39 -0700695
Nick Piggin46453a62006-03-22 00:07:58 -0800696 if (pagezone != zone) {
697 if (zone)
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700698 spin_unlock_irqrestore(&zone->lru_lock,
699 flags);
Nick Piggin46453a62006-03-22 00:07:58 -0800700 zone = pagezone;
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700701 spin_lock_irqsave(&zone->lru_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700702 }
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700703
704 lruvec = mem_cgroup_page_lruvec(page, zone);
Nick Piggin725d7042006-09-25 23:30:55 -0700705 VM_BUG_ON(!PageLRU(page));
Nick Piggin67453912006-03-22 00:08:00 -0800706 __ClearPageLRU(page);
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700707 del_page_from_lru_list(page, lruvec, page_off_lru(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700708 }
Nick Piggin46453a62006-03-22 00:07:58 -0800709
Konstantin Khlebnikovcc598502012-01-10 15:07:04 -0800710 list_add(&page->lru, &pages_to_free);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700711 }
712 if (zone)
Hisashi Hifumi902aaed2007-10-16 01:24:52 -0700713 spin_unlock_irqrestore(&zone->lru_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700714
Konstantin Khlebnikovcc598502012-01-10 15:07:04 -0800715 free_hot_cold_page_list(&pages_to_free, cold);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700716}
Miklos Szeredi0be85572010-10-27 15:34:46 -0700717EXPORT_SYMBOL(release_pages);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700718
719/*
720 * The pages which we're about to release may be in the deferred lru-addition
721 * queues. That would prevent them from really being freed right now. That's
722 * OK from a correctness point of view but is inefficient - those pages may be
723 * cache-warm and we want to give them back to the page allocator ASAP.
724 *
725 * So __pagevec_release() will drain those queues here. __pagevec_lru_add()
726 * and __pagevec_lru_add_active() call release_pages() directly to avoid
727 * mutual recursion.
728 */
729void __pagevec_release(struct pagevec *pvec)
730{
731 lru_add_drain();
732 release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
733 pagevec_reinit(pvec);
734}
Steve French7f285702005-11-01 10:22:55 -0800735EXPORT_SYMBOL(__pagevec_release);
736
Hugh Dickins12d27102012-01-12 17:19:52 -0800737#ifdef CONFIG_TRANSPARENT_HUGEPAGE
Andrea Arcangeli71e3aac2011-01-13 15:46:52 -0800738/* used by __split_huge_page_refcount() */
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700739void lru_add_page_tail(struct page *page, struct page *page_tail,
740 struct lruvec *lruvec)
Andrea Arcangeli71e3aac2011-01-13 15:46:52 -0800741{
Hugh Dickins75121022012-03-05 14:59:18 -0800742 int uninitialized_var(active);
Andrea Arcangeli71e3aac2011-01-13 15:46:52 -0800743 enum lru_list lru;
744 const int file = 0;
Andrea Arcangeli71e3aac2011-01-13 15:46:52 -0800745
746 VM_BUG_ON(!PageHead(page));
747 VM_BUG_ON(PageCompound(page_tail));
748 VM_BUG_ON(PageLRU(page_tail));
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700749 VM_BUG_ON(NR_CPUS != 1 &&
750 !spin_is_locked(&lruvec_zone(lruvec)->lru_lock));
Andrea Arcangeli71e3aac2011-01-13 15:46:52 -0800751
752 SetPageLRU(page_tail);
753
Hugh Dickins39b5f292012-10-08 16:33:18 -0700754 if (page_evictable(page_tail)) {
Andrea Arcangeli71e3aac2011-01-13 15:46:52 -0800755 if (PageActive(page)) {
756 SetPageActive(page_tail);
757 active = 1;
758 lru = LRU_ACTIVE_ANON;
759 } else {
760 active = 0;
761 lru = LRU_INACTIVE_ANON;
762 }
Andrea Arcangeli71e3aac2011-01-13 15:46:52 -0800763 } else {
764 SetPageUnevictable(page_tail);
Hugh Dickins12d27102012-01-12 17:19:52 -0800765 lru = LRU_UNEVICTABLE;
766 }
767
768 if (likely(PageLRU(page)))
769 list_add_tail(&page_tail->lru, &page->lru);
770 else {
771 struct list_head *list_head;
772 /*
773 * Head page has not yet been counted, as an hpage,
774 * so we must account for each subpage individually.
775 *
776 * Use the standard add function to put page_tail on the list,
777 * but then correct its position so they all end up in order.
778 */
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700779 add_page_to_lru_list(page_tail, lruvec, lru);
Hugh Dickins12d27102012-01-12 17:19:52 -0800780 list_head = page_tail->lru.prev;
781 list_move_tail(&page_tail->lru, list_head);
Andrea Arcangeli71e3aac2011-01-13 15:46:52 -0800782 }
Hugh Dickins75121022012-03-05 14:59:18 -0800783
784 if (!PageUnevictable(page))
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700785 update_page_reclaim_stat(lruvec, file, active);
Andrea Arcangeli71e3aac2011-01-13 15:46:52 -0800786}
Hugh Dickins12d27102012-01-12 17:19:52 -0800787#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
Andrea Arcangeli71e3aac2011-01-13 15:46:52 -0800788
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700789static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
790 void *arg)
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700791{
792 enum lru_list lru = (enum lru_list)arg;
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700793 int file = is_file_lru(lru);
794 int active = is_active_lru(lru);
795
796 VM_BUG_ON(PageActive(page));
797 VM_BUG_ON(PageUnevictable(page));
798 VM_BUG_ON(PageLRU(page));
799
800 SetPageLRU(page);
801 if (active)
802 SetPageActive(page);
Hugh Dickinsfa9add62012-05-29 15:07:09 -0700803 add_page_to_lru_list(page, lruvec, lru);
804 update_page_reclaim_stat(lruvec, file, active);
Shaohua Li3dd7ae82011-03-22 16:33:45 -0700805}
806
Linus Torvalds1da177e2005-04-16 15:20:36 -0700807/*
Linus Torvalds1da177e2005-04-16 15:20:36 -0700808 * Add the passed pages to the LRU, then drop the caller's refcount
809 * on them. Reinitialises the caller's pagevec.
810 */
Hugh Dickins5095ae832012-01-12 17:19:58 -0800811void __pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700812{
Lee Schermerhorn894bc312008-10-18 20:26:39 -0700813 VM_BUG_ON(is_unevictable_lru(lru));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700814
Hugh Dickins5095ae832012-01-12 17:19:58 -0800815 pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn, (void *)lru);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700816}
Hugh Dickins5095ae832012-01-12 17:19:58 -0800817EXPORT_SYMBOL(__pagevec_lru_add);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700818
Linus Torvalds1da177e2005-04-16 15:20:36 -0700819/**
820 * pagevec_lookup - gang pagecache lookup
821 * @pvec: Where the resulting pages are placed
822 * @mapping: The address_space to search
823 * @start: The starting page index
824 * @nr_pages: The maximum number of pages
825 *
826 * pagevec_lookup() will search for and return a group of up to @nr_pages pages
827 * in the mapping. The pages are placed in @pvec. pagevec_lookup() takes a
828 * reference against the pages in @pvec.
829 *
830 * The search returns a group of mapping-contiguous pages with ascending
831 * indexes. There may be holes in the indices due to not-present pages.
832 *
833 * pagevec_lookup() returns the number of pages which were found.
834 */
835unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
836 pgoff_t start, unsigned nr_pages)
837{
838 pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
839 return pagevec_count(pvec);
840}
Christoph Hellwig78539fd2006-01-11 20:47:41 +1100841EXPORT_SYMBOL(pagevec_lookup);
842
Linus Torvalds1da177e2005-04-16 15:20:36 -0700843unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
844 pgoff_t *index, int tag, unsigned nr_pages)
845{
846 pvec->nr = find_get_pages_tag(mapping, index, tag,
847 nr_pages, pvec->pages);
848 return pagevec_count(pvec);
849}
Steve French7f285702005-11-01 10:22:55 -0800850EXPORT_SYMBOL(pagevec_lookup_tag);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700851
Linus Torvalds1da177e2005-04-16 15:20:36 -0700852/*
853 * Perform any setup for the swap system
854 */
855void __init swap_setup(void)
856{
Jan Beulich44813742009-09-21 17:03:05 -0700857 unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT);
Peter Zijlstrae0bf68d2007-10-16 23:25:46 -0700858#ifdef CONFIG_SWAP
Shaohua Li33806f02013-02-22 16:34:37 -0800859 int i;
860
861 bdi_init(swapper_spaces[0].backing_dev_info);
862 for (i = 0; i < MAX_SWAPFILES; i++) {
863 spin_lock_init(&swapper_spaces[i].tree_lock);
864 INIT_LIST_HEAD(&swapper_spaces[i].i_mmap_nonlinear);
865 }
Peter Zijlstrae0bf68d2007-10-16 23:25:46 -0700866#endif
867
Linus Torvalds1da177e2005-04-16 15:20:36 -0700868 /* Use a smaller cluster for small-memory machines */
869 if (megs < 16)
870 page_cluster = 2;
871 else
872 page_cluster = 3;
873 /*
874 * Right now other parts of the system means that we
875 * _really_ don't want to cluster much more
876 */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700877}