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
218    unsigned long inactive, isolated;
219
220    inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
221                    zone_page_state(zone, NR_INACTIVE_ANON);
222    isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
223                    zone_page_state(zone, NR_ISOLATED_ANON);
224
225    return isolated > inactive;
226}
227
228/*
229 * Isolate all pages that can be migrated from the block pointed to by
230 * the migrate scanner within compact_control.
231 */
232static unsigned long isolate_migratepages(struct zone *zone,
233                    struct compact_control *cc)
234{
235    unsigned long low_pfn, end_pfn;
236    struct list_head *migratelist = &cc->migratepages;
237
238    /* Do not scan outside zone boundaries */
239    low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
240
241    /* Only scan within a pageblock boundary */
242    end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
243
244    /* Do not cross the free scanner or scan within a memory hole */
245    if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
246        cc->migrate_pfn = end_pfn;
247        return 0;
248    }
249
250    /*
251     * Ensure that there are not too many pages isolated from the LRU
252     * list by either parallel reclaimers or compaction. If there are,
253     * delay for some time until fewer pages are isolated
254     */
255    while (unlikely(too_many_isolated(zone))) {
256        congestion_wait(BLK_RW_ASYNC, HZ/10);
257
258        if (fatal_signal_pending(current))
259            return 0;
260    }
261
262    /* Time to isolate some pages for migration */
263    spin_lock_irq(&zone->lru_lock);
264    for (; low_pfn < end_pfn; low_pfn++) {
265        struct page *page;
266        if (!pfn_valid_within(low_pfn))
267            continue;
268
269        /* Get the page and skip if free */
270        page = pfn_to_page(low_pfn);
271        if (PageBuddy(page))
272            continue;
273
274        /* Try isolate the page */
275        if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
276            continue;
277
278        /* Successfully isolated */
279        del_page_from_lru_list(zone, page, page_lru(page));
280        list_add(&page->lru, migratelist);
281        mem_cgroup_del_lru(page);
282        cc->nr_migratepages++;
283
284        /* Avoid isolating too much */
285        if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
286            break;
287    }
288
289    acct_isolated(zone, cc);
290
291    spin_unlock_irq(&zone->lru_lock);
292    cc->migrate_pfn = low_pfn;
293
294    return cc->nr_migratepages;
295}
296
297/*
298 * This is a migrate-callback that "allocates" freepages by taking pages
299 * from the isolated freelists in the block we are migrating to.
300 */
301static struct page *compaction_alloc(struct page *migratepage,
302                    unsigned long data,
303                    int **result)
304{
305    struct compact_control *cc = (struct compact_control *)data;
306    struct page *freepage;
307
308    /* Isolate free pages if necessary */
309    if (list_empty(&cc->freepages)) {
310        isolate_freepages(cc->zone, cc);
311
312        if (list_empty(&cc->freepages))
313            return NULL;
314    }
315
316    freepage = list_entry(cc->freepages.next, struct page, lru);
317    list_del(&freepage->lru);
318    cc->nr_freepages--;
319
320    return freepage;
321}
322
323/*
324 * We cannot control nr_migratepages and nr_freepages fully when migration is
325 * running as migrate_pages() has no knowledge of compact_control. When
326 * migration is complete, we count the number of pages on the lists by hand.
327 */
328static void update_nr_listpages(struct compact_control *cc)
329{
330    int nr_migratepages = 0;
331    int nr_freepages = 0;
332    struct page *page;
333
334    list_for_each_entry(page, &cc->migratepages, lru)
335        nr_migratepages++;
336    list_for_each_entry(page, &cc->freepages, lru)
337        nr_freepages++;
338
339    cc->nr_migratepages = nr_migratepages;
340    cc->nr_freepages = nr_freepages;
341}
342
343static int compact_finished(struct zone *zone,
344                        struct compact_control *cc)
345{
346    unsigned int order;
347    unsigned long watermark = low_wmark_pages(zone) + (1 << cc->order);
348
349    if (fatal_signal_pending(current))
350        return COMPACT_PARTIAL;
351
352    /* Compaction run completes if the migrate and free scanner meet */
353    if (cc->free_pfn <= cc->migrate_pfn)
354        return COMPACT_COMPLETE;
355
356    /* Compaction run is not finished if the watermark is not met */
357    if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
358        return COMPACT_CONTINUE;
359
360    if (cc->order == -1)
361        return COMPACT_CONTINUE;
362
363    /* Direct compactor: Is a suitable page free? */
364    for (order = cc->order; order < MAX_ORDER; order++) {
365        /* Job done if page is free of the right migratetype */
366        if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
367            return COMPACT_PARTIAL;
368
369        /* Job done if allocation would set block type */
370        if (order >= pageblock_order && zone->free_area[order].nr_free)
371            return COMPACT_PARTIAL;
372    }
373
374    return COMPACT_CONTINUE;
375}
376
377static int compact_zone(struct zone *zone, struct compact_control *cc)
378{
379    int ret;
380
381    /* Setup to move all movable pages to the end of the zone */
382    cc->migrate_pfn = zone->zone_start_pfn;
383    cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
384    cc->free_pfn &= ~(pageblock_nr_pages-1);
385
386    migrate_prep_local();
387
388    while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
389        unsigned long nr_migrate, nr_remaining;
390
391        if (!isolate_migratepages(zone, cc))
392            continue;
393
394        nr_migrate = cc->nr_migratepages;
395        migrate_pages(&cc->migratepages, compaction_alloc,
396                        (unsigned long)cc, 0);
397        update_nr_listpages(cc);
398        nr_remaining = cc->nr_migratepages;
399
400        count_vm_event(COMPACTBLOCKS);
401        count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
402        if (nr_remaining)
403            count_vm_events(COMPACTPAGEFAILED, nr_remaining);
404
405        /* Release LRU pages not migrated */
406        if (!list_empty(&cc->migratepages)) {
407            putback_lru_pages(&cc->migratepages);
408            cc->nr_migratepages = 0;
409        }
410
411    }
412
413    /* Release free pages and check accounting */
414    cc->nr_freepages -= release_freepages(&cc->freepages);
415    VM_BUG_ON(cc->nr_freepages != 0);
416
417    return ret;
418}
419
420static unsigned long compact_zone_order(struct zone *zone,
421                        int order, gfp_t gfp_mask)
422{
423    struct compact_control cc = {
424        .nr_freepages = 0,
425        .nr_migratepages = 0,
426        .order = order,
427        .migratetype = allocflags_to_migratetype(gfp_mask),
428        .zone = zone,
429    };
430    INIT_LIST_HEAD(&cc.freepages);
431    INIT_LIST_HEAD(&cc.migratepages);
432
433    return compact_zone(zone, &cc);
434}
435
436int sysctl_extfrag_threshold = 500;
437
438/**
439 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
440 * @zonelist: The zonelist used for the current allocation
441 * @order: The order of the current allocation
442 * @gfp_mask: The GFP mask of the current allocation
443 * @nodemask: The allowed nodes to allocate from
444 *
445 * This is the main entry point for direct page compaction.
446 */
447unsigned long try_to_compact_pages(struct zonelist *zonelist,
448            int order, gfp_t gfp_mask, nodemask_t *nodemask)
449{
450    enum zone_type high_zoneidx = gfp_zone(gfp_mask);
451    int may_enter_fs = gfp_mask & __GFP_FS;
452    int may_perform_io = gfp_mask & __GFP_IO;
453    unsigned long watermark;
454    struct zoneref *z;
455    struct zone *zone;
456    int rc = COMPACT_SKIPPED;
457
458    /*
459     * Check whether it is worth even starting compaction. The order check is
460     * made because an assumption is made that the page allocator can satisfy
461     * the "cheaper" orders without taking special steps
462     */
463    if (order <= PAGE_ALLOC_COSTLY_ORDER || !may_enter_fs || !may_perform_io)
464        return rc;
465
466    count_vm_event(COMPACTSTALL);
467
468    /* Compact each zone in the list */
469    for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
470                                nodemask) {
471        int fragindex;
472        int status;
473
474        /*
475         * Watermarks for order-0 must be met for compaction. Note
476         * the 2UL. This is because during migration, copies of
477         * pages need to be allocated and for a short time, the
478         * footprint is higher
479         */
480        watermark = low_wmark_pages(zone) + (2UL << order);
481        if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
482            continue;
483
484        /*
485         * fragmentation index determines if allocation failures are
486         * due to low memory or external fragmentation
487         *
488         * index of -1 implies allocations might succeed depending
489         * on watermarks
490         * index towards 0 implies failure is due to lack of memory
491         * index towards 1000 implies failure is due to fragmentation
492         *
493         * Only compact if a failure would be due to fragmentation.
494         */
495        fragindex = fragmentation_index(zone, order);
496        if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
497            continue;
498
499        if (fragindex == -1 && zone_watermark_ok(zone, order, watermark, 0, 0)) {
500            rc = COMPACT_PARTIAL;
501            break;
502        }
503
504        status = compact_zone_order(zone, order, gfp_mask);
505        rc = max(status, rc);
506
507        if (zone_watermark_ok(zone, order, watermark, 0, 0))
508            break;
509    }
510
511    return rc;
512}
513
514
515/* Compact all zones within a node */
516static int compact_node(int nid)
517{
518    int zoneid;
519    pg_data_t *pgdat;
520    struct zone *zone;
521
522    if (nid < 0 || nid >= nr_node_ids || !node_online(nid))
523        return -EINVAL;
524    pgdat = NODE_DATA(nid);
525
526    /* Flush pending updates to the LRU lists */
527    lru_add_drain_all();
528
529    for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
530        struct compact_control cc = {
531            .nr_freepages = 0,
532            .nr_migratepages = 0,
533            .order = -1,
534        };
535
536        zone = &pgdat->node_zones[zoneid];
537        if (!populated_zone(zone))
538            continue;
539
540        cc.zone = zone;
541        INIT_LIST_HEAD(&cc.freepages);
542        INIT_LIST_HEAD(&cc.migratepages);
543
544        compact_zone(zone, &cc);
545
546        VM_BUG_ON(!list_empty(&cc.freepages));
547        VM_BUG_ON(!list_empty(&cc.migratepages));
548    }
549
550    return 0;
551}
552
553/* Compact all nodes in the system */
554static int compact_nodes(void)
555{
556    int nid;
557
558    for_each_online_node(nid)
559        compact_node(nid);
560
561    return COMPACT_COMPLETE;
562}
563
564/* The written value is actually unused, all memory is compacted */
565int sysctl_compact_memory;
566
567/* This is the entry point for compacting all nodes via /proc/sys/vm */
568int sysctl_compaction_handler(struct ctl_table *table, int write,
569            void __user *buffer, size_t *length, loff_t *ppos)
570{
571    if (write)
572        return compact_nodes();
573
574    return 0;
575}
576
577int sysctl_extfrag_handler(struct ctl_table *table, int write,
578            void __user *buffer, size_t *length, loff_t *ppos)
579{
580    proc_dointvec_minmax(table, write, buffer, length, ppos);
581
582    return 0;
583}
584
585#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
586ssize_t sysfs_compact_node(struct sys_device *dev,
587            struct sysdev_attribute *attr,
588            const char *buf, size_t count)
589{
590    compact_node(dev->id);
591
592    return count;
593}
594static SYSDEV_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
595
596int compaction_register_node(struct node *node)
597{
598    return sysdev_create_file(&node->sysdev, &attr_compact);
599}
600
601void compaction_unregister_node(struct node *node)
602{
603    return sysdev_remove_file(&node->sysdev, &attr_compact);
604}
605#endif /* CONFIG_SYSFS && CONFIG_NUMA */
606

Archive Download this file



interactive