Root/mm/compaction.c

1/*
2 * linux/mm/compaction.c
3 *
4 * Memory compaction for the reduction of external fragmentation. Note that
5 * this heavily depends upon page migration to do all the real heavy
6 * lifting
7 *
8 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
9 */
10#include <linux/swap.h>
11#include <linux/migrate.h>
12#include <linux/compaction.h>
13#include <linux/mm_inline.h>
14#include <linux/backing-dev.h>
15#include <linux/sysctl.h>
16#include <linux/sysfs.h>
17#include "internal.h"
18
19/*
20 * compact_control is used to track pages being migrated and the free pages
21 * they are being migrated to during memory compaction. The free_pfn starts
22 * at the end of a zone and migrate_pfn begins at the start. Movable pages
23 * are moved to the end of a zone during a compaction run and the run
24 * completes when free_pfn <= migrate_pfn
25 */
26struct compact_control {
27    struct list_head freepages; /* List of free pages to migrate to */
28    struct list_head migratepages; /* List of pages being migrated */
29    unsigned long nr_freepages; /* Number of isolated free pages */
30    unsigned long nr_migratepages; /* Number of pages to migrate */
31    unsigned long free_pfn; /* isolate_freepages search base */
32    unsigned long migrate_pfn; /* isolate_migratepages search base */
33
34    /* Account for isolated anon and file pages */
35    unsigned long nr_anon;
36    unsigned long nr_file;
37
38    unsigned int order; /* order a direct compactor needs */
39    int migratetype; /* MOVABLE, RECLAIMABLE etc */
40    struct zone *zone;
41};
42
43static unsigned long release_freepages(struct list_head *freelist)
44{
45    struct page *page, *next;
46    unsigned long count = 0;
47
48    list_for_each_entry_safe(page, next, freelist, lru) {
49        list_del(&page->lru);
50        __free_page(page);
51        count++;
52    }
53
54    return count;
55}
56
57/* Isolate free pages onto a private freelist. Must hold zone->lock */
58static unsigned long isolate_freepages_block(struct zone *zone,
59                unsigned long blockpfn,
60                struct list_head *freelist)
61{
62    unsigned long zone_end_pfn, end_pfn;
63    int total_isolated = 0;
64    struct page *cursor;
65
66    /* Get the last PFN we should scan for free pages at */
67    zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
68    end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
69
70    /* Find the first usable PFN in the block to initialse page cursor */
71    for (; blockpfn < end_pfn; blockpfn++) {
72        if (pfn_valid_within(blockpfn))
73            break;
74    }
75    cursor = pfn_to_page(blockpfn);
76
77    /* Isolate free pages. This assumes the block is valid */
78    for (; blockpfn < end_pfn; blockpfn++, cursor++) {
79        int isolated, i;
80        struct page *page = cursor;
81
82        if (!pfn_valid_within(blockpfn))
83            continue;
84
85        if (!PageBuddy(page))
86            continue;
87
88        /* Found a free page, break it into order-0 pages */
89        isolated = split_free_page(page);
90        total_isolated += isolated;
91        for (i = 0; i < isolated; i++) {
92            list_add(&page->lru, freelist);
93            page++;
94        }
95
96        /* If a page was split, advance to the end of it */
97        if (isolated) {
98            blockpfn += isolated - 1;
99            cursor += isolated - 1;
100        }
101    }
102
103    return total_isolated;
104}
105
106/* Returns true if the page is within a block suitable for migration to */
107static bool suitable_migration_target(struct page *page)
108{
109
110    int migratetype = get_pageblock_migratetype(page);
111
112    /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
113    if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
114        return false;
115
116    /* If the page is a large free page, then allow migration */
117    if (PageBuddy(page) && page_order(page) >= pageblock_order)
118        return true;
119
120    /* If the block is MIGRATE_MOVABLE, allow migration */
121    if (migratetype == MIGRATE_MOVABLE)
122        return true;
123
124    /* Otherwise skip the block */
125    return false;
126}
127
128/*
129 * Based on information in the current compact_control, find blocks
130 * suitable for isolating free pages from and then isolate them.
131 */
132static void isolate_freepages(struct zone *zone,
133                struct compact_control *cc)
134{
135    struct page *page;
136    unsigned long high_pfn, low_pfn, pfn;
137    unsigned long flags;
138    int nr_freepages = cc->nr_freepages;
139    struct list_head *freelist = &cc->freepages;
140
141    pfn = cc->free_pfn;
142    low_pfn = cc->migrate_pfn + pageblock_nr_pages;
143    high_pfn = low_pfn;
144
145    /*
146     * Isolate free pages until enough are available to migrate the
147     * pages on cc->migratepages. We stop searching if the migrate
148     * and free page scanners meet or enough free pages are isolated.
149     */
150    spin_lock_irqsave(&zone->lock, flags);
151    for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
152                    pfn -= pageblock_nr_pages) {
153        unsigned long isolated;
154
155        if (!pfn_valid(pfn))
156            continue;
157
158        /*
159         * Check for overlapping nodes/zones. It's possible on some
160         * configurations to have a setup like
161         * node0 node1 node0
162         * i.e. it's possible that all pages within a zones range of
163         * pages do not belong to a single zone.
164         */
165        page = pfn_to_page(pfn);
166        if (page_zone(page) != zone)
167            continue;
168
169        /* Check the block is suitable for migration */
170        if (!suitable_migration_target(page))
171            continue;
172
173        /* Found a block suitable for isolating free pages from */
174        isolated = isolate_freepages_block(zone, pfn, freelist);
175        nr_freepages += isolated;
176
177        /*
178         * Record the highest PFN we isolated pages from. When next
179         * looking for free pages, the search will restart here as
180         * page migration may have returned some pages to the allocator
181         */
182        if (isolated)
183            high_pfn = max(high_pfn, pfn);
184    }
185    spin_unlock_irqrestore(&zone->lock, flags);
186
187    /* split_free_page does not map the pages */
188    list_for_each_entry(page, freelist, lru) {
189        arch_alloc_page(page, 0);
190        kernel_map_pages(page, 1, 1);
191    }
192
193    cc->free_pfn = high_pfn;
194    cc->nr_freepages = nr_freepages;
195}
196
197/* Update the number of anon and file isolated pages in the zone */
198static void acct_isolated(struct zone *zone, struct compact_control *cc)
199{
200    struct page *page;
201    unsigned int count[NR_LRU_LISTS] = { 0, };
202
203    list_for_each_entry(page, &cc->migratepages, lru) {
204        int lru = page_lru_base_type(page);
205        count[lru]++;
206    }
207
208    cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
209    cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
210    __mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
211    __mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
212}
213
214/* Similar to reclaim, but different enough that they don't share logic */
215static bool too_many_isolated(struct zone *zone)
216{
217    unsigned long active, inactive, isolated;
218
219    inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
220                    zone_page_state(zone, NR_INACTIVE_ANON);
221    active = zone_page_state(zone, NR_ACTIVE_FILE) +
222                    zone_page_state(zone, NR_ACTIVE_ANON);
223    isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
224                    zone_page_state(zone, NR_ISOLATED_ANON);
225
226    return isolated > (inactive + active) / 2;
227}
228
229/*
230 * Isolate all pages that can be migrated from the block pointed to by
231 * the migrate scanner within compact_control.
232 */
233static unsigned long isolate_migratepages(struct zone *zone,
234                    struct compact_control *cc)
235{
236    unsigned long low_pfn, end_pfn;
237    struct list_head *migratelist = &cc->migratepages;
238
239    /* Do not scan outside zone boundaries */
240    low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
241
242    /* Only scan within a pageblock boundary */
243    end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
244
245    /* Do not cross the free scanner or scan within a memory hole */
246    if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
247        cc->migrate_pfn = end_pfn;
248        return 0;
249    }
250
251    /*
252     * Ensure that there are not too many pages isolated from the LRU
253     * list by either parallel reclaimers or compaction. If there are,
254     * delay for some time until fewer pages are isolated
255     */
256    while (unlikely(too_many_isolated(zone))) {
257        congestion_wait(BLK_RW_ASYNC, HZ/10);
258
259        if (fatal_signal_pending(current))
260            return 0;
261    }
262
263    /* Time to isolate some pages for migration */
264    spin_lock_irq(&zone->lru_lock);
265    for (; low_pfn < end_pfn; low_pfn++) {
266        struct page *page;
267        if (!pfn_valid_within(low_pfn))
268            continue;
269
270        /* Get the page and skip if free */
271        page = pfn_to_page(low_pfn);
272        if (PageBuddy(page))
273            continue;
274
275        /* Try isolate the page */
276        if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
277            continue;
278
279        /* Successfully isolated */
280        del_page_from_lru_list(zone, page, page_lru(page));
281        list_add(&page->lru, migratelist);
282        mem_cgroup_del_lru(page);
283        cc->nr_migratepages++;
284
285        /* Avoid isolating too much */
286        if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
287            break;
288    }
289
290    acct_isolated(zone, cc);
291
292    spin_unlock_irq(&zone->lru_lock);
293    cc->migrate_pfn = low_pfn;
294
295    return cc->nr_migratepages;
296}
297
298/*
299 * This is a migrate-callback that "allocates" freepages by taking pages
300 * from the isolated freelists in the block we are migrating to.
301 */
302static struct page *compaction_alloc(struct page *migratepage,
303                    unsigned long data,
304                    int **result)
305{
306    struct compact_control *cc = (struct compact_control *)data;
307    struct page *freepage;
308
309    /* Isolate free pages if necessary */
310    if (list_empty(&cc->freepages)) {
311        isolate_freepages(cc->zone, cc);
312
313        if (list_empty(&cc->freepages))
314            return NULL;
315    }
316
317    freepage = list_entry(cc->freepages.next, struct page, lru);
318    list_del(&freepage->lru);
319    cc->nr_freepages--;
320
321    return freepage;
322}
323
324/*
325 * We cannot control nr_migratepages and nr_freepages fully when migration is
326 * running as migrate_pages() has no knowledge of compact_control. When
327 * migration is complete, we count the number of pages on the lists by hand.
328 */
329static void update_nr_listpages(struct compact_control *cc)
330{
331    int nr_migratepages = 0;
332    int nr_freepages = 0;
333    struct page *page;
334
335    list_for_each_entry(page, &cc->migratepages, lru)
336        nr_migratepages++;
337    list_for_each_entry(page, &cc->freepages, lru)
338        nr_freepages++;
339
340    cc->nr_migratepages = nr_migratepages;
341    cc->nr_freepages = nr_freepages;
342}
343
344static int compact_finished(struct zone *zone,
345                        struct compact_control *cc)
346{
347    unsigned int order;
348    unsigned long watermark = low_wmark_pages(zone) + (1 << cc->order);
349
350    if (fatal_signal_pending(current))
351        return COMPACT_PARTIAL;
352
353    /* Compaction run completes if the migrate and free scanner meet */
354    if (cc->free_pfn <= cc->migrate_pfn)
355        return COMPACT_COMPLETE;
356
357    /* Compaction run is not finished if the watermark is not met */
358    if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
359        return COMPACT_CONTINUE;
360
361    if (cc->order == -1)
362        return COMPACT_CONTINUE;
363
364    /* Direct compactor: Is a suitable page free? */
365    for (order = cc->order; order < MAX_ORDER; order++) {
366        /* Job done if page is free of the right migratetype */
367        if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
368            return COMPACT_PARTIAL;
369
370        /* Job done if allocation would set block type */
371        if (order >= pageblock_order && zone->free_area[order].nr_free)
372            return COMPACT_PARTIAL;
373    }
374
375    return COMPACT_CONTINUE;
376}
377
378static int compact_zone(struct zone *zone, struct compact_control *cc)
379{
380    int ret;
381
382    /* Setup to move all movable pages to the end of the zone */
383    cc->migrate_pfn = zone->zone_start_pfn;
384    cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
385    cc->free_pfn &= ~(pageblock_nr_pages-1);
386
387    migrate_prep_local();
388
389    while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
390        unsigned long nr_migrate, nr_remaining;
391
392        if (!isolate_migratepages(zone, cc))
393            continue;
394
395        nr_migrate = cc->nr_migratepages;
396        migrate_pages(&cc->migratepages, compaction_alloc,
397                        (unsigned long)cc, 0);
398        update_nr_listpages(cc);
399        nr_remaining = cc->nr_migratepages;
400
401        count_vm_event(COMPACTBLOCKS);
402        count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
403        if (nr_remaining)
404            count_vm_events(COMPACTPAGEFAILED, nr_remaining);
405
406        /* Release LRU pages not migrated */
407        if (!list_empty(&cc->migratepages)) {
408            putback_lru_pages(&cc->migratepages);
409            cc->nr_migratepages = 0;
410        }
411
412    }
413
414    /* Release free pages and check accounting */
415    cc->nr_freepages -= release_freepages(&cc->freepages);
416    VM_BUG_ON(cc->nr_freepages != 0);
417
418    return ret;
419}
420
421static unsigned long compact_zone_order(struct zone *zone,
422                        int order, gfp_t gfp_mask)
423{
424    struct compact_control cc = {
425        .nr_freepages = 0,
426        .nr_migratepages = 0,
427        .order = order,
428        .migratetype = allocflags_to_migratetype(gfp_mask),
429        .zone = zone,
430    };
431    INIT_LIST_HEAD(&cc.freepages);
432    INIT_LIST_HEAD(&cc.migratepages);
433
434    return compact_zone(zone, &cc);
435}
436
437int sysctl_extfrag_threshold = 500;
438
439/**
440 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
441 * @zonelist: The zonelist used for the current allocation
442 * @order: The order of the current allocation
443 * @gfp_mask: The GFP mask of the current allocation
444 * @nodemask: The allowed nodes to allocate from
445 *
446 * This is the main entry point for direct page compaction.
447 */
448unsigned long try_to_compact_pages(struct zonelist *zonelist,
449            int order, gfp_t gfp_mask, nodemask_t *nodemask)
450{
451    enum zone_type high_zoneidx = gfp_zone(gfp_mask);
452    int may_enter_fs = gfp_mask & __GFP_FS;
453    int may_perform_io = gfp_mask & __GFP_IO;
454    unsigned long watermark;
455    struct zoneref *z;
456    struct zone *zone;
457    int rc = COMPACT_SKIPPED;
458
459    /*
460     * Check whether it is worth even starting compaction. The order check is
461     * made because an assumption is made that the page allocator can satisfy
462     * the "cheaper" orders without taking special steps
463     */
464    if (order <= PAGE_ALLOC_COSTLY_ORDER || !may_enter_fs || !may_perform_io)
465        return rc;
466
467    count_vm_event(COMPACTSTALL);
468
469    /* Compact each zone in the list */
470    for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
471                                nodemask) {
472        int fragindex;
473        int status;
474
475        /*
476         * Watermarks for order-0 must be met for compaction. Note
477         * the 2UL. This is because during migration, copies of
478         * pages need to be allocated and for a short time, the
479         * footprint is higher
480         */
481        watermark = low_wmark_pages(zone) + (2UL << order);
482        if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
483            continue;
484
485        /*
486         * fragmentation index determines if allocation failures are
487         * due to low memory or external fragmentation
488         *
489         * index of -1 implies allocations might succeed depending
490         * on watermarks
491         * index towards 0 implies failure is due to lack of memory
492         * index towards 1000 implies failure is due to fragmentation
493         *
494         * Only compact if a failure would be due to fragmentation.
495         */
496        fragindex = fragmentation_index(zone, order);
497        if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
498            continue;
499
500        if (fragindex == -1 && zone_watermark_ok(zone, order, watermark, 0, 0)) {
501            rc = COMPACT_PARTIAL;
502            break;
503        }
504
505        status = compact_zone_order(zone, order, gfp_mask);
506        rc = max(status, rc);
507
508        if (zone_watermark_ok(zone, order, watermark, 0, 0))
509            break;
510    }
511
512    return rc;
513}
514
515
516/* Compact all zones within a node */
517static int compact_node(int nid)
518{
519    int zoneid;
520    pg_data_t *pgdat;
521    struct zone *zone;
522
523    if (nid < 0 || nid >= nr_node_ids || !node_online(nid))
524        return -EINVAL;
525    pgdat = NODE_DATA(nid);
526
527    /* Flush pending updates to the LRU lists */
528    lru_add_drain_all();
529
530    for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
531        struct compact_control cc = {
532            .nr_freepages = 0,
533            .nr_migratepages = 0,
534            .order = -1,
535        };
536
537        zone = &pgdat->node_zones[zoneid];
538        if (!populated_zone(zone))
539            continue;
540
541        cc.zone = zone;
542        INIT_LIST_HEAD(&cc.freepages);
543        INIT_LIST_HEAD(&cc.migratepages);
544
545        compact_zone(zone, &cc);
546
547        VM_BUG_ON(!list_empty(&cc.freepages));
548        VM_BUG_ON(!list_empty(&cc.migratepages));
549    }
550
551    return 0;
552}
553
554/* Compact all nodes in the system */
555static int compact_nodes(void)
556{
557    int nid;
558
559    for_each_online_node(nid)
560        compact_node(nid);
561
562    return COMPACT_COMPLETE;
563}
564
565/* The written value is actually unused, all memory is compacted */
566int sysctl_compact_memory;
567
568/* This is the entry point for compacting all nodes via /proc/sys/vm */
569int sysctl_compaction_handler(struct ctl_table *table, int write,
570            void __user *buffer, size_t *length, loff_t *ppos)
571{
572    if (write)
573        return compact_nodes();
574
575    return 0;
576}
577
578int sysctl_extfrag_handler(struct ctl_table *table, int write,
579            void __user *buffer, size_t *length, loff_t *ppos)
580{
581    proc_dointvec_minmax(table, write, buffer, length, ppos);
582
583    return 0;
584}
585
586#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
587ssize_t sysfs_compact_node(struct sys_device *dev,
588            struct sysdev_attribute *attr,
589            const char *buf, size_t count)
590{
591    compact_node(dev->id);
592
593    return count;
594}
595static SYSDEV_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
596
597int compaction_register_node(struct node *node)
598{
599    return sysdev_create_file(&node->sysdev, &attr_compact);
600}
601
602void compaction_unregister_node(struct node *node)
603{
604    return sysdev_remove_file(&node->sysdev, &attr_compact);
605}
606#endif /* CONFIG_SYSFS && CONFIG_NUMA */
607

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