/* * linux/mm/compaction.c * * Memory compaction for the reduction of external fragmentation. Note that * this heavily depends upon page migration to do all the real heavy * lifting * * Copyright IBM Corp. 2007-2010 Mel Gorman */ #include #include #include #include #include #include #include #include #include #include #include "internal.h" #ifdef CONFIG_COMPACTION static inline void count_compact_event(enum vm_event_item item) { count_vm_event(item); } static inline void count_compact_events(enum vm_event_item item, long delta) { count_vm_events(item, delta); } #else #define count_compact_event(item) do { } while (0) #define count_compact_events(item, delta) do { } while (0) #endif #if defined CONFIG_COMPACTION || defined CONFIG_CMA #ifdef CONFIG_TRACEPOINTS static const char *const compaction_status_string[] = { "deferred", "skipped", "continue", "partial", "complete", "no_suitable_page", "not_suitable_zone", }; #endif #define CREATE_TRACE_POINTS #include static unsigned long release_freepages(struct list_head *freelist) { struct page *page, *next; unsigned long high_pfn = 0; list_for_each_entry_safe(page, next, freelist, lru) { unsigned long pfn = page_to_pfn(page); list_del(&page->lru); __free_page(page); if (pfn > high_pfn) high_pfn = pfn; } return high_pfn; } static void map_pages(struct list_head *list) { struct page *page; list_for_each_entry(page, list, lru) { arch_alloc_page(page, 0); kernel_map_pages(page, 1, 1); kasan_alloc_pages(page, 0); } } static inline bool migrate_async_suitable(int migratetype) { return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE; } /* * Check that the whole (or subset of) a pageblock given by the interval of * [start_pfn, end_pfn) is valid and within the same zone, before scanning it * with the migration of free compaction scanner. The scanners then need to * use only pfn_valid_within() check for arches that allow holes within * pageblocks. * * Return struct page pointer of start_pfn, or NULL if checks were not passed. * * It's possible on some configurations to have a setup like node0 node1 node0 * i.e. it's possible that all pages within a zones range of pages do not * belong to a single zone. We assume that a border between node0 and node1 * can occur within a single pageblock, but not a node0 node1 node0 * interleaving within a single pageblock. It is therefore sufficient to check * the first and last page of a pageblock and avoid checking each individual * page in a pageblock. */ static struct page *pageblock_pfn_to_page(unsigned long start_pfn, unsigned long end_pfn, struct zone *zone) { struct page *start_page; struct page *end_page; /* end_pfn is one past the range we are checking */ end_pfn--; if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn)) return NULL; start_page = pfn_to_page(start_pfn); if (page_zone(start_page) != zone) return NULL; end_page = pfn_to_page(end_pfn); /* This gives a shorter code than deriving page_zone(end_page) */ if (page_zone_id(start_page) != page_zone_id(end_page)) return NULL; return start_page; } #ifdef CONFIG_COMPACTION /* Do not skip compaction more than 64 times */ #define COMPACT_MAX_DEFER_SHIFT 6 /* * Compaction is deferred when compaction fails to result in a page * allocation success. 1 << compact_defer_limit compactions are skipped up * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT */ void defer_compaction(struct zone *zone, int order) { zone->compact_considered = 0; zone->compact_defer_shift++; if (order < zone->compact_order_failed) zone->compact_order_failed = order; if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT) zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT; trace_mm_compaction_defer_compaction(zone, order); } /* Returns true if compaction should be skipped this time */ bool compaction_deferred(struct zone *zone, int order) { unsigned long defer_limit = 1UL << zone->compact_defer_shift; if (order < zone->compact_order_failed) return false; /* Avoid possible overflow */ if (++zone->compact_considered > defer_limit) zone->compact_considered = defer_limit; if (zone->compact_considered >= defer_limit) return false; trace_mm_compaction_deferred(zone, order); return true; } /* * Update defer tracking counters after successful compaction of given order, * which means an allocation either succeeded (alloc_success == true) or is * expected to succeed. */ void compaction_defer_reset(struct zone *zone, int order, bool alloc_success) { if (alloc_success) { zone->compact_considered = 0; zone->compact_defer_shift = 0; } if (order >= zone->compact_order_failed) zone->compact_order_failed = order + 1; trace_mm_compaction_defer_reset(zone, order); } /* Returns true if restarting compaction after many failures */ bool compaction_restarting(struct zone *zone, int order) { if (order < zone->compact_order_failed) return false; return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT && zone->compact_considered >= 1UL << zone->compact_defer_shift; } /* Returns true if the pageblock should be scanned for pages to isolate. */ static inline bool isolation_suitable(struct compact_control *cc, struct page *page) { if (cc->ignore_skip_hint) return true; return !get_pageblock_skip(page); } static void reset_cached_positions(struct zone *zone) { zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn; zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn; zone->compact_cached_free_pfn = zone_end_pfn(zone); } /* * This function is called to clear all cached information on pageblocks that * should be skipped for page isolation when the migrate and free page scanner * meet. */ static void __reset_isolation_suitable(struct zone *zone) { unsigned long start_pfn = zone->zone_start_pfn; unsigned long end_pfn = zone_end_pfn(zone); unsigned long pfn; zone->compact_blockskip_flush = false; /* Walk the zone and mark every pageblock as suitable for isolation */ for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) { struct page *page; cond_resched(); if (!pfn_valid(pfn)) continue; page = pfn_to_page(pfn); if (zone != page_zone(page)) continue; clear_pageblock_skip(page); } reset_cached_positions(zone); } void reset_isolation_suitable(pg_data_t *pgdat) { int zoneid; for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { struct zone *zone = &pgdat->node_zones[zoneid]; if (!populated_zone(zone)) continue; /* Only flush if a full compaction finished recently */ if (zone->compact_blockskip_flush) __reset_isolation_suitable(zone); } } /* * If no pages were isolated then mark this pageblock to be skipped in the * future. The information is later cleared by __reset_isolation_suitable(). */ static void update_pageblock_skip(struct compact_control *cc, struct page *page, unsigned long nr_isolated, bool migrate_scanner) { struct zone *zone = cc->zone; unsigned long pfn; if (cc->ignore_skip_hint) return; if (!page) return; if (nr_isolated) return; set_pageblock_skip(page); pfn = page_to_pfn(page); /* Update where async and sync compaction should restart */ if (migrate_scanner) { if (pfn > zone->compact_cached_migrate_pfn[0]) zone->compact_cached_migrate_pfn[0] = pfn; if (cc->mode != MIGRATE_ASYNC && pfn > zone->compact_cached_migrate_pfn[1]) zone->compact_cached_migrate_pfn[1] = pfn; } else { if (pfn < zone->compact_cached_free_pfn) zone->compact_cached_free_pfn = pfn; } } #else static inline bool isolation_suitable(struct compact_control *cc, struct page *page) { return true; } static void update_pageblock_skip(struct compact_control *cc, struct page *page, unsigned long nr_isolated, bool migrate_scanner) { } #endif /* CONFIG_COMPACTION */ /* * Compaction requires the taking of some coarse locks that are potentially * very heavily contended. For async compaction, back out if the lock cannot * be taken immediately. For sync compaction, spin on the lock if needed. * * Returns true if the lock is held * Returns false if the lock is not held and compaction should abort */ static bool compact_trylock_irqsave(spinlock_t *lock, unsigned long *flags, struct compact_control *cc) { if (cc->mode == MIGRATE_ASYNC) { if (!spin_trylock_irqsave(lock, *flags)) { cc->contended = COMPACT_CONTENDED_LOCK; return false; } } else { spin_lock_irqsave(lock, *flags); } return true; } /* * Compaction requires the taking of some coarse locks that are potentially * very heavily contended. The lock should be periodically unlocked to avoid * having disabled IRQs for a long time, even when there is nobody waiting on * the lock. It might also be that allowing the IRQs will result in * need_resched() becoming true. If scheduling is needed, async compaction * aborts. Sync compaction schedules. * Either compaction type will also abort if a fatal signal is pending. * In either case if the lock was locked, it is dropped and not regained. * * Returns true if compaction should abort due to fatal signal pending, or * async compaction due to need_resched() * Returns false when compaction can continue (sync compaction might have * scheduled) */ static bool compact_unlock_should_abort(spinlock_t *lock, unsigned long flags, bool *locked, struct compact_control *cc) { if (*locked) { spin_unlock_irqrestore(lock, flags); *locked = false; } if (fatal_signal_pending(current)) { cc->contended = COMPACT_CONTENDED_SCHED; return true; } if (need_resched()) { if (cc->mode == MIGRATE_ASYNC) { cc->contended = COMPACT_CONTENDED_SCHED; return true; } cond_resched(); } return false; } /* * Aside from avoiding lock contention, compaction also periodically checks * need_resched() and either schedules in sync compaction or aborts async * compaction. This is similar to what compact_unlock_should_abort() does, but * is used where no lock is concerned. * * Returns false when no scheduling was needed, or sync compaction scheduled. * Returns true when async compaction should abort. */ static inline bool compact_should_abort(struct compact_control *cc) { /* async compaction aborts if contended */ if (need_resched()) { if (cc->mode == MIGRATE_ASYNC) { cc->contended = COMPACT_CONTENDED_SCHED; return true; } cond_resched(); } return false; } /* * Isolate free pages onto a private freelist. If @strict is true, will abort * returning 0 on any invalid PFNs or non-free pages inside of the pageblock * (even though it may still end up isolating some pages). */ static unsigned long isolate_freepages_block(struct compact_control *cc, unsigned long *start_pfn, unsigned long end_pfn, struct list_head *freelist, bool strict) { int nr_scanned = 0, total_isolated = 0; struct page *cursor, *valid_page = NULL; unsigned long flags = 0; bool locked = false; unsigned long blockpfn = *start_pfn; cursor = pfn_to_page(blockpfn); /* Isolate free pages. */ for (; blockpfn < end_pfn; blockpfn++, cursor++) { int isolated, i; struct page *page = cursor; /* * Periodically drop the lock (if held) regardless of its * contention, to give chance to IRQs. Abort if fatal signal * pending or async compaction detects need_resched() */ if (!(blockpfn % SWAP_CLUSTER_MAX) && compact_unlock_should_abort(&cc->zone->lock, flags, &locked, cc)) break; nr_scanned++; if (!pfn_valid_within(blockpfn)) goto isolate_fail; if (!valid_page) valid_page = page; /* * For compound pages such as THP and hugetlbfs, we can save * potentially a lot of iterations if we skip them at once. * The check is racy, but we can consider only valid values * and the only danger is skipping too much. */ if (PageCompound(page)) { unsigned int comp_order = compound_order(page); if (likely(comp_order < MAX_ORDER)) { blockpfn += (1UL << comp_order) - 1; cursor += (1UL << comp_order) - 1; } goto isolate_fail; } if (!PageBuddy(page)) goto isolate_fail; /* * If we already hold the lock, we can skip some rechecking. * Note that if we hold the lock now, checked_pageblock was * already set in some previous iteration (or strict is true), * so it is correct to skip the suitable migration target * recheck as well. */ if (!locked) { /* * The zone lock must be held to isolate freepages. * Unfortunately this is a very coarse lock and can be * heavily contended if there are parallel allocations * or parallel compactions. For async compaction do not * spin on the lock and we acquire the lock as late as * possible. */ locked = compact_trylock_irqsave(&cc->zone->lock, &flags, cc); if (!locked) break; /* Recheck this is a buddy page under lock */ if (!PageBuddy(page)) goto isolate_fail; } /* Found a free page, break it into order-0 pages */ isolated = split_free_page(page); total_isolated += isolated; for (i = 0; i < isolated; i++) { list_add(&page->lru, freelist); page++; } /* If a page was split, advance to the end of it */ if (isolated) { cc->nr_freepages += isolated; if (!strict && cc->nr_migratepages <= cc->nr_freepages) { blockpfn += isolated; break; } blockpfn += isolated - 1; cursor += isolated - 1; continue; } isolate_fail: if (strict) break; else continue; } /* * There is a tiny chance that we have read bogus compound_order(), * so be careful to not go outside of the pageblock. */ if (unlikely(blockpfn > end_pfn)) blockpfn = end_pfn; trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn, nr_scanned, total_isolated); /* Record how far we have got within the block */ *start_pfn = blockpfn; /* * If strict isolation is requested by CMA then check that all the * pages requested were isolated. If there were any failures, 0 is * returned and CMA will fail. */ if (strict && blockpfn < end_pfn) total_isolated = 0; if (locked) spin_unlock_irqrestore(&cc->zone->lock, flags); /* Update the pageblock-skip if the whole pageblock was scanned */ if (blockpfn == end_pfn) update_pageblock_skip(cc, valid_page, total_isolated, false); count_compact_events(COMPACTFREE_SCANNED, nr_scanned); if (total_isolated) count_compact_events(COMPACTISOLATED, total_isolated); return total_isolated; } /** * isolate_freepages_range() - isolate free pages. * @start_pfn: The first PFN to start isolating. * @end_pfn: The one-past-last PFN. * * Non-free pages, invalid PFNs, or zone boundaries within the * [start_pfn, end_pfn) range are considered errors, cause function to * undo its actions and return zero. * * Otherwise, function returns one-past-the-last PFN of isolated page * (which may be greater then end_pfn if end fell in a middle of * a free page). */ unsigned long isolate_freepages_range(struct compact_control *cc, unsigned long start_pfn, unsigned long end_pfn) { unsigned long isolated, pfn, block_end_pfn; LIST_HEAD(freelist); pfn = start_pfn; block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages); for (; pfn < end_pfn; pfn += isolated, block_end_pfn += pageblock_nr_pages) { /* Protect pfn from changing by isolate_freepages_block */ unsigned long isolate_start_pfn = pfn; block_end_pfn = min(block_end_pfn, end_pfn); /* * pfn could pass the block_end_pfn if isolated freepage * is more than pageblock order. In this case, we adjust * scanning range to right one. */ if (pfn >= block_end_pfn) { block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages); block_end_pfn = min(block_end_pfn, end_pfn); } if (!pageblock_pfn_to_page(pfn, block_end_pfn, cc->zone)) break; isolated = isolate_freepages_block(cc, &isolate_start_pfn, block_end_pfn, &freelist, true); /* * In strict mode, isolate_freepages_block() returns 0 if * there are any holes in the block (ie. invalid PFNs or * non-free pages). */ if (!isolated) break; /* * If we managed to isolate pages, it is always (1 << n) * * pageblock_nr_pages for some non-negative n. (Max order * page may span two pageblocks). */ } /* split_free_page does not map the pages */ map_pages(&freelist); if (pfn < end_pfn) { /* Loop terminated early, cleanup. */ release_freepages(&freelist); return 0; } /* We don't use freelists for anything. */ return pfn; } /* Update the number of anon and file isolated pages in the zone */ static void acct_isolated(struct zone *zone, struct compact_control *cc) { struct page *page; unsigned int count[2] = { 0, }; if (list_empty(&cc->migratepages)) return; list_for_each_entry(page, &cc->migratepages, lru) count[!!page_is_file_cache(page)]++; mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]); mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]); } /* Similar to reclaim, but different enough that they don't share logic */ static bool too_many_isolated(struct zone *zone) { unsigned long active, inactive, isolated; inactive = zone_page_state(zone, NR_INACTIVE_FILE) + zone_page_state(zone, NR_INACTIVE_ANON); active = zone_page_state(zone, NR_ACTIVE_FILE) + zone_page_state(zone, NR_ACTIVE_ANON); isolated = zone_page_state(zone, NR_ISOLATED_FILE) + zone_page_state(zone, NR_ISOLATED_ANON); return isolated > (inactive + active) / 2; } /** * isolate_migratepages_block() - isolate all migrate-able pages within * a single pageblock * @cc: Compaction control structure. * @low_pfn: The first PFN to isolate * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock * @isolate_mode: Isolation mode to be used. * * Isolate all pages that can be migrated from the range specified by * [low_pfn, end_pfn). The range is expected to be within same pageblock. * Returns zero if there is a fatal signal pending, otherwise PFN of the * first page that was not scanned (which may be both less, equal to or more * than end_pfn). * * The pages are isolated on cc->migratepages list (not required to be empty), * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field * is neither read nor updated. */ static unsigned long isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, unsigned long end_pfn, isolate_mode_t isolate_mode) { struct zone *zone = cc->zone; unsigned long nr_scanned = 0, nr_isolated = 0; struct list_head *migratelist = &cc->migratepages; struct lruvec *lruvec; unsigned long flags = 0; bool locked = false; struct page *page = NULL, *valid_page = NULL; unsigned long start_pfn = low_pfn; /* * Ensure that there are not too many pages isolated from the LRU * list by either parallel reclaimers or compaction. If there are, * delay for some time until fewer pages are isolated */ while (unlikely(too_many_isolated(zone))) { /* async migration should just abort */ if (cc->mode == MIGRATE_ASYNC) return 0; congestion_wait(BLK_RW_ASYNC, HZ/10); if (fatal_signal_pending(current)) return 0; } if (compact_should_abort(cc)) return 0; /* Time to isolate some pages for migration */ for (; low_pfn < end_pfn; low_pfn++) { bool is_lru; /* * Periodically drop the lock (if held) regardless of its * contention, to give chance to IRQs. Abort async compaction * if contended. */ if (!(low_pfn % SWAP_CLUSTER_MAX) && compact_unlock_should_abort(&zone->lru_lock, flags, &locked, cc)) break; if (!pfn_valid_within(low_pfn)) continue; nr_scanned++; page = pfn_to_page(low_pfn); if (!valid_page) valid_page = page; /* * Skip if free. We read page order here without zone lock * which is generally unsafe, but the race window is small and * the worst thing that can happen is that we skip some * potential isolation targets. */ if (PageBuddy(page)) { unsigned long freepage_order = page_order_unsafe(page); /* * Without lock, we cannot be sure that what we got is * a valid page order. Consider only values in the * valid order range to prevent low_pfn overflow. */ if (freepage_order > 0 && freepage_order < MAX_ORDER) low_pfn += (1UL << freepage_order) - 1; continue; } /* * Check may be lockless but that's ok as we recheck later. * It's possible to migrate LRU pages and balloon pages * Skip any other type of page */ is_lru = PageLRU(page); if (!is_lru) { if (unlikely(balloon_page_movable(page))) { if (balloon_page_isolate(page)) { /* Successfully isolated */ goto isolate_success; } } } /* * Regardless of being on LRU, compound pages such as THP and * hugetlbfs are not to be compacted. We can potentially save * a lot of iterations if we skip them at once. The check is * racy, but we can consider only valid values and the only * danger is skipping too much. */ if (PageCompound(page)) { unsigned int comp_order = compound_order(page); if (likely(comp_order < MAX_ORDER)) low_pfn += (1UL << comp_order) - 1; continue; } if (!is_lru) continue; /* * Migration will fail if an anonymous page is pinned in memory, * so avoid taking lru_lock and isolating it unnecessarily in an * admittedly racy check. */ if (!page_mapping(page) && page_count(page) > page_mapcount(page)) continue; /* If we already hold the lock, we can skip some rechecking */ if (!locked) { locked = compact_trylock_irqsave(&zone->lru_lock, &flags, cc); if (!locked) break; /* Recheck PageLRU and PageCompound under lock */ if (!PageLRU(page)) continue; /* * Page become compound since the non-locked check, * and it's on LRU. It can only be a THP so the order * is safe to read and it's 0 for tail pages. */ if (unlikely(PageCompound(page))) { low_pfn += (1UL << compound_order(page)) - 1; continue; } } lruvec = mem_cgroup_page_lruvec(page, zone); /* Try isolate the page */ if (__isolate_lru_page(page, isolate_mode) != 0) continue; VM_BUG_ON_PAGE(PageCompound(page), page); /* Successfully isolated */ del_page_from_lru_list(page, lruvec, page_lru(page)); isolate_success: list_add(&page->lru, migratelist); cc->nr_migratepages++; nr_isolated++; /* Avoid isolating too much */ if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) { ++low_pfn; break; } } /* * The PageBuddy() check could have potentially brought us outside * the range to be scanned. */ if (unlikely(low_pfn > end_pfn)) low_pfn = end_pfn; if (locked) spin_unlock_irqrestore(&zone->lru_lock, flags); /* * Update the pageblock-skip information and cached scanner pfn, * if the whole pageblock was scanned without isolating any page. */ if (low_pfn == end_pfn) update_pageblock_skip(cc, valid_page, nr_isolated, true); trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn, nr_scanned, nr_isolated); count_compact_events(COMPACTMIGRATE_SCANNED, nr_scanned); if (nr_isolated) count_compact_events(COMPACTISOLATED, nr_isolated); return low_pfn; } /** * isolate_migratepages_range() - isolate migrate-able pages in a PFN range * @cc: Compaction control structure. * @start_pfn: The first PFN to start isolating. * @end_pfn: The one-past-last PFN. * * Returns zero if isolation fails fatally due to e.g. pending signal. * Otherwise, function returns one-past-the-last PFN of isolated page * (which may be greater than end_pfn if end fell in a middle of a THP page). */ unsigned long isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn, unsigned long end_pfn) { unsigned long pfn, block_end_pfn; /* Scan block by block. First and last block may be incomplete */ pfn = start_pfn; block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages); for (; pfn < end_pfn; pfn = block_end_pfn, block_end_pfn += pageblock_nr_pages) { block_end_pfn = min(block_end_pfn, end_pfn); if (!pageblock_pfn_to_page(pfn, block_end_pfn, cc->zone)) continue; pfn = isolate_migratepages_block(cc, pfn, block_end_pfn, ISOLATE_UNEVICTABLE); /* * In case of fatal failure, release everything that might * have been isolated in the previous iteration, and signal * the failure back to caller. */ if (!pfn) { putback_movable_pages(&cc->migratepages); cc->nr_migratepages = 0; break; } if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) break; } acct_isolated(cc->zone, cc); return pfn; } #endif /* CONFIG_COMPACTION || CONFIG_CMA */ #ifdef CONFIG_COMPACTION /* Returns true if the page is within a block suitable for migration to */ static bool suitable_migration_target(struct page *page) { /* If the page is a large free page, then disallow migration */ if (PageBuddy(page)) { /* * We are checking page_order without zone->lock taken. But * the only small danger is that we skip a potentially suitable * pageblock, so it's not worth to check order for valid range. */ if (page_order_unsafe(page) >= pageblock_order) return false; } /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */ if (migrate_async_suitable(get_pageblock_migratetype(page))) return true; /* Otherwise skip the block */ return false; } /* * Test whether the free scanner has reached the same or lower pageblock than * the migration scanner, and compaction should thus terminate. */ static inline bool compact_scanners_met(struct compact_control *cc) { return (cc->free_pfn >> pageblock_order) <= (cc->migrate_pfn >> pageblock_order); } /* * Based on information in the current compact_control, find blocks * suitable for isolating free pages from and then isolate them. */ static void isolate_freepages(struct compact_control *cc) { struct zone *zone = cc->zone; struct page *page; unsigned long block_start_pfn; /* start of current pageblock */ unsigned long isolate_start_pfn; /* exact pfn we start at */ unsigned long block_end_pfn; /* end of current pageblock */ unsigned long low_pfn; /* lowest pfn scanner is able to scan */ struct list_head *freelist = &cc->freepages; /* * Initialise the free scanner. The starting point is where we last * successfully isolated from, zone-cached value, or the end of the * zone when isolating for the first time. For looping we also need * this pfn aligned down to the pageblock boundary, because we do * block_start_pfn -= pageblock_nr_pages in the for loop. * For ending point, take care when isolating in last pageblock of a * a zone which ends in the middle of a pageblock. * The low boundary is the end of the pageblock the migration scanner * is using. */ isolate_start_pfn = cc->free_pfn; block_start_pfn = cc->free_pfn & ~(pageblock_nr_pages-1); block_end_pfn = min(block_start_pfn + pageblock_nr_pages, zone_end_pfn(zone)); low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages); /* * Isolate free pages until enough are available to migrate the * pages on cc->migratepages. We stop searching if the migrate * and free page scanners meet or enough free pages are isolated. */ for (; block_start_pfn >= low_pfn; block_end_pfn = block_start_pfn, block_start_pfn -= pageblock_nr_pages, isolate_start_pfn = block_start_pfn) { /* * This can iterate a massively long zone without finding any * suitable migration targets, so periodically check if we need * to schedule, or even abort async compaction. */ if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)) && compact_should_abort(cc)) break; page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn, zone); if (!page) continue; /* Check the block is suitable for migration */ if (!suitable_migration_target(page)) continue; /* If isolation recently failed, do not retry */ if (!isolation_suitable(cc, page)) continue; /* Found a block suitable for isolating free pages from. */ isolate_freepages_block(cc, &isolate_start_pfn, block_end_pfn, freelist, false); /* * If we isolated enough freepages, or aborted due to async * compaction being contended, terminate the loop. * Remember where the free scanner should restart next time, * which is where isolate_freepages_block() left off. * But if it scanned the whole pageblock, isolate_start_pfn * now points at block_end_pfn, which is the start of the next * pageblock. * In that case we will however want to restart at the start * of the previous pageblock. */ if ((cc->nr_freepages >= cc->nr_migratepages) || cc->contended) { if (isolate_start_pfn >= block_end_pfn) isolate_start_pfn = block_start_pfn - pageblock_nr_pages; break; } else { /* * isolate_freepages_block() should not terminate * prematurely unless contended, or isolated enough */ VM_BUG_ON(isolate_start_pfn < block_end_pfn); } } /* split_free_page does not map the pages */ map_pages(freelist); /* * Record where the free scanner will restart next time. Either we * broke from the loop and set isolate_start_pfn based on the last * call to isolate_freepages_block(), or we met the migration scanner * and the loop terminated due to isolate_start_pfn < low_pfn */ cc->free_pfn = isolate_start_pfn; } /* * This is a migrate-callback that "allocates" freepages by taking pages * from the isolated freelists in the block we are migrating to. */ static struct page *compaction_alloc(struct page *migratepage, unsigned long data, int **result) { struct compact_control *cc = (struct compact_control *)data; struct page *freepage; /* * Isolate free pages if necessary, and if we are not aborting due to * contention. */ if (list_empty(&cc->freepages)) { if (!cc->contended) isolate_freepages(cc); if (list_empty(&cc->freepages)) return NULL; } freepage = list_entry(cc->freepages.next, struct page, lru); list_del(&freepage->lru); cc->nr_freepages--; return freepage; } /* * This is a migrate-callback that "frees" freepages back to the isolated * freelist. All pages on the freelist are from the same zone, so there is no * special handling needed for NUMA. */ static void compaction_free(struct page *page, unsigned long data) { struct compact_control *cc = (struct compact_control *)data; list_add(&page->lru, &cc->freepages); cc->nr_freepages++; } /* possible outcome of isolate_migratepages */ typedef enum { ISOLATE_ABORT, /* Abort compaction now */ ISOLATE_NONE, /* No pages isolated, continue scanning */ ISOLATE_SUCCESS, /* Pages isolated, migrate */ } isolate_migrate_t; /* * Allow userspace to control policy on scanning the unevictable LRU for * compactable pages. */ int sysctl_compact_unevictable_allowed __read_mostly = 1; /* * Isolate all pages that can be migrated from the first suitable block, * starting at the block pointed to by the migrate scanner pfn within * compact_control. */ static isolate_migrate_t isolate_migratepages(struct zone *zone, struct compact_control *cc) { unsigned long low_pfn, end_pfn; unsigned long isolate_start_pfn; struct page *page; const isolate_mode_t isolate_mode = (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) | (cc->mode == MIGRATE_ASYNC ? ISOLATE_ASYNC_MIGRATE : 0); /* * Start at where we last stopped, or beginning of the zone as * initialized by compact_zone() */ low_pfn = cc->migrate_pfn; /* Only scan within a pageblock boundary */ end_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages); /* * Iterate over whole pageblocks until we find the first suitable. * Do not cross the free scanner. */ for (; end_pfn <= cc->free_pfn; low_pfn = end_pfn, end_pfn += pageblock_nr_pages) { /* * This can potentially iterate a massively long zone with * many pageblocks unsuitable, so periodically check if we * need to schedule, or even abort async compaction. */ if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)) && compact_should_abort(cc)) break; page = pageblock_pfn_to_page(low_pfn, end_pfn, zone); if (!page) continue; /* If isolation recently failed, do not retry */ if (!isolation_suitable(cc, page)) continue; /* * For async compaction, also only scan in MOVABLE blocks. * Async compaction is optimistic to see if the minimum amount * of work satisfies the allocation. */ if (cc->mode == MIGRATE_ASYNC && !migrate_async_suitable(get_pageblock_migratetype(page))) continue; /* Perform the isolation */ isolate_start_pfn = low_pfn; low_pfn = isolate_migratepages_block(cc, low_pfn, end_pfn, isolate_mode); if (!low_pfn || cc->contended) { acct_isolated(zone, cc); return ISOLATE_ABORT; } /* * Record where we could have freed pages by migration and not * yet flushed them to buddy allocator. * - this is the lowest page that could have been isolated and * then freed by migration. */ if (cc->nr_migratepages && !cc->last_migrated_pfn) cc->last_migrated_pfn = isolate_start_pfn; /* * Either we isolated something and proceed with migration. Or * we failed and compact_zone should decide if we should * continue or not. */ break; } acct_isolated(zone, cc); /* Record where migration scanner will be restarted. */ cc->migrate_pfn = low_pfn; return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE; } /* * order == -1 is expected when compacting via * /proc/sys/vm/compact_memory */ static inline bool is_via_compact_memory(int order) { return order == -1; } static int __compact_finished(struct zone *zone, struct compact_control *cc, const int migratetype) { unsigned int order; unsigned long watermark; if (cc->contended || fatal_signal_pending(current)) return COMPACT_PARTIAL; /* Compaction run completes if the migrate and free scanner meet */ if (compact_scanners_met(cc)) { /* Let the next compaction start anew. */ reset_cached_positions(zone); /* * Mark that the PG_migrate_skip information should be cleared * by kswapd when it goes to sleep. kswapd does not set the * flag itself as the decision to be clear should be directly * based on an allocation request. */ if (!current_is_kswapd()) zone->compact_blockskip_flush = true; return COMPACT_COMPLETE; } if (is_via_compact_memory(cc->order)) return COMPACT_CONTINUE; /* Compaction run is not finished if the watermark is not met */ watermark = low_wmark_pages(zone); if (!zone_watermark_ok(zone, cc->order, watermark, cc->classzone_idx, cc->alloc_flags)) return COMPACT_CONTINUE; /* Direct compactor: Is a suitable page free? */ for (order = cc->order; order < MAX_ORDER; order++) { struct free_area *area = &zone->free_area[order]; bool can_steal; /* Job done if page is free of the right migratetype */ if (!list_empty(&area->free_list[migratetype])) return COMPACT_PARTIAL; #ifdef CONFIG_CMA /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */ if (migratetype == MIGRATE_MOVABLE && !list_empty(&area->free_list[MIGRATE_CMA])) return COMPACT_PARTIAL; #endif /* * Job done if allocation would steal freepages from * other migratetype buddy lists. */ if (find_suitable_fallback(area, order, migratetype, true, &can_steal) != -1) return COMPACT_PARTIAL; } return COMPACT_NO_SUITABLE_PAGE; } static int compact_finished(struct zone *zone, struct compact_control *cc, const int migratetype) { int ret; ret = __compact_finished(zone, cc, migratetype); trace_mm_compaction_finished(zone, cc->order, ret); if (ret == COMPACT_NO_SUITABLE_PAGE) ret = COMPACT_CONTINUE; return ret; } /* * compaction_suitable: Is this suitable to run compaction on this zone now? * Returns * COMPACT_SKIPPED - If there are too few free pages for compaction * COMPACT_PARTIAL - If the allocation would succeed without compaction * COMPACT_CONTINUE - If compaction should run now */ static unsigned long __compaction_suitable(struct zone *zone, int order, int alloc_flags, int classzone_idx) { int fragindex; unsigned long watermark; if (is_via_compact_memory(order)) return COMPACT_CONTINUE; watermark = low_wmark_pages(zone); /* * If watermarks for high-order allocation are already met, there * should be no need for compaction at all. */ if (zone_watermark_ok(zone, order, watermark, classzone_idx, alloc_flags)) return COMPACT_PARTIAL; /* * Watermarks for order-0 must be met for compaction. Note the 2UL. * This is because during migration, copies of pages need to be * allocated and for a short time, the footprint is higher */ watermark += (2UL << order); if (!zone_watermark_ok(zone, 0, watermark, classzone_idx, alloc_flags)) return COMPACT_SKIPPED; /* * fragmentation index determines if allocation failures are due to * low memory or external fragmentation * * index of -1000 would imply allocations might succeed depending on * watermarks, but we already failed the high-order watermark check * index towards 0 implies failure is due to lack of memory * index towards 1000 implies failure is due to fragmentation * * Only compact if a failure would be due to fragmentation. */ fragindex = fragmentation_index(zone, order); if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold) return COMPACT_NOT_SUITABLE_ZONE; return COMPACT_CONTINUE; } unsigned long compaction_suitable(struct zone *zone, int order, int alloc_flags, int classzone_idx) { unsigned long ret; ret = __compaction_suitable(zone, order, alloc_flags, classzone_idx); trace_mm_compaction_suitable(zone, order, ret); if (ret == COMPACT_NOT_SUITABLE_ZONE) ret = COMPACT_SKIPPED; return ret; } static int compact_zone(struct zone *zone, struct compact_control *cc) { int ret; unsigned long start_pfn = zone->zone_start_pfn; unsigned long end_pfn = zone_end_pfn(zone); const int migratetype = gfpflags_to_migratetype(cc->gfp_mask); const bool sync = cc->mode != MIGRATE_ASYNC; ret = compaction_suitable(zone, cc->order, cc->alloc_flags, cc->classzone_idx); switch (ret) { case COMPACT_PARTIAL: case COMPACT_SKIPPED: /* Compaction is likely to fail */ return ret; case COMPACT_CONTINUE: /* Fall through to compaction */ ; } /* * Clear pageblock skip if there were failures recently and compaction * is about to be retried after being deferred. kswapd does not do * this reset as it'll reset the cached information when going to sleep. */ if (compaction_restarting(zone, cc->order) && !current_is_kswapd()) __reset_isolation_suitable(zone); /* * Setup to move all movable pages to the end of the zone. Used cached * information on where the scanners should start but check that it * is initialised by ensuring the values are within zone boundaries. */ cc->migrate_pfn = zone->compact_cached_migrate_pfn[sync]; cc->free_pfn = zone->compact_cached_free_pfn; if (cc->free_pfn < start_pfn || cc->free_pfn > end_pfn) { cc->free_pfn = end_pfn & ~(pageblock_nr_pages-1); zone->compact_cached_free_pfn = cc->free_pfn; } if (cc->migrate_pfn < start_pfn || cc->migrate_pfn > end_pfn) { cc->migrate_pfn = start_pfn; zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn; zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn; } cc->last_migrated_pfn = 0; trace_mm_compaction_begin(start_pfn, cc->migrate_pfn, cc->free_pfn, end_pfn, sync); migrate_prep_local(); while ((ret = compact_finished(zone, cc, migratetype)) == COMPACT_CONTINUE) { int err; switch (isolate_migratepages(zone, cc)) { case ISOLATE_ABORT: ret = COMPACT_PARTIAL; putback_movable_pages(&cc->migratepages); cc->nr_migratepages = 0; goto out; case ISOLATE_NONE: /* * We haven't isolated and migrated anything, but * there might still be unflushed migrations from * previous cc->order aligned block. */ goto check_drain; case ISOLATE_SUCCESS: ; } err = migrate_pages(&cc->migratepages, compaction_alloc, compaction_free, (unsigned long)cc, cc->mode, MR_COMPACTION); trace_mm_compaction_migratepages(cc->nr_migratepages, err, &cc->migratepages); /* All pages were either migrated or will be released */ cc->nr_migratepages = 0; if (err) { putback_movable_pages(&cc->migratepages); /* * migrate_pages() may return -ENOMEM when scanners meet * and we want compact_finished() to detect it */ if (err == -ENOMEM && !compact_scanners_met(cc)) { ret = COMPACT_PARTIAL; goto out; } } check_drain: /* * Has the migration scanner moved away from the previous * cc->order aligned block where we migrated from? If yes, * flush the pages that were freed, so that they can merge and * compact_finished() can detect immediately if allocation * would succeed. */ if (cc->order > 0 && cc->last_migrated_pfn) { int cpu; unsigned long current_block_start = cc->migrate_pfn & ~((1UL << cc->order) - 1); if (cc->last_migrated_pfn < current_block_start) { cpu = get_cpu(); lru_add_drain_cpu(cpu); drain_local_pages(zone); put_cpu(); /* No more flushing until we migrate again */ cc->last_migrated_pfn = 0; } } } out: /* * Release free pages and update where the free scanner should restart, * so we don't leave any returned pages behind in the next attempt. */ if (cc->nr_freepages > 0) { unsigned long free_pfn = release_freepages(&cc->freepages); cc->nr_freepages = 0; VM_BUG_ON(free_pfn == 0); /* The cached pfn is always the first in a pageblock */ free_pfn &= ~(pageblock_nr_pages-1); /* * Only go back, not forward. The cached pfn might have been * already reset to zone end in compact_finished() */ if (free_pfn > zone->compact_cached_free_pfn) zone->compact_cached_free_pfn = free_pfn; } trace_mm_compaction_end(start_pfn, cc->migrate_pfn, cc->free_pfn, end_pfn, sync, ret); return ret; } static unsigned long compact_zone_order(struct zone *zone, int order, gfp_t gfp_mask, enum migrate_mode mode, int *contended, int alloc_flags, int classzone_idx) { unsigned long ret; struct compact_control cc = { .nr_freepages = 0, .nr_migratepages = 0, .order = order, .gfp_mask = gfp_mask, .zone = zone, .mode = mode, .alloc_flags = alloc_flags, .classzone_idx = classzone_idx, }; INIT_LIST_HEAD(&cc.freepages); INIT_LIST_HEAD(&cc.migratepages); ret = compact_zone(zone, &cc); VM_BUG_ON(!list_empty(&cc.freepages)); VM_BUG_ON(!list_empty(&cc.migratepages)); *contended = cc.contended; return ret; } int sysctl_extfrag_threshold = 500; /** * try_to_compact_pages - Direct compact to satisfy a high-order allocation * @gfp_mask: The GFP mask of the current allocation * @order: The order of the current allocation * @alloc_flags: The allocation flags of the current allocation * @ac: The context of current allocation * @mode: The migration mode for async, sync light, or sync migration * @contended: Return value that determines if compaction was aborted due to * need_resched() or lock contention * * This is the main entry point for direct page compaction. */ unsigned long try_to_compact_pages(gfp_t gfp_mask, unsigned int order, int alloc_flags, const struct alloc_context *ac, enum migrate_mode mode, int *contended) { int may_enter_fs = gfp_mask & __GFP_FS; int may_perform_io = gfp_mask & __GFP_IO; struct zoneref *z; struct zone *zone; int rc = COMPACT_DEFERRED; int all_zones_contended = COMPACT_CONTENDED_LOCK; /* init for &= op */ *contended = COMPACT_CONTENDED_NONE; /* Check if the GFP flags allow compaction */ if (!order || !may_enter_fs || !may_perform_io) return COMPACT_SKIPPED; trace_mm_compaction_try_to_compact_pages(order, gfp_mask, mode); /* Compact each zone in the list */ for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx, ac->nodemask) { int status; int zone_contended; if (compaction_deferred(zone, order)) continue; status = compact_zone_order(zone, order, gfp_mask, mode, &zone_contended, alloc_flags, ac->classzone_idx); rc = max(status, rc); /* * It takes at least one zone that wasn't lock contended * to clear all_zones_contended. */ all_zones_contended &= zone_contended; /* If a normal allocation would succeed, stop compacting */ if (zone_watermark_ok(zone, order, low_wmark_pages(zone), ac->classzone_idx, alloc_flags)) { /* * We think the allocation will succeed in this zone, * but it is not certain, hence the false. The caller * will repeat this with true if allocation indeed * succeeds in this zone. */ compaction_defer_reset(zone, order, false); /* * It is possible that async compaction aborted due to * need_resched() and the watermarks were ok thanks to * somebody else freeing memory. The allocation can * however still fail so we better signal the * need_resched() contention anyway (this will not * prevent the allocation attempt). */ if (zone_contended == COMPACT_CONTENDED_SCHED) *contended = COMPACT_CONTENDED_SCHED; goto break_loop; } if (mode != MIGRATE_ASYNC && status == COMPACT_COMPLETE) { /* * We think that allocation won't succeed in this zone * so we defer compaction there. If it ends up * succeeding after all, it will be reset. */ defer_compaction(zone, order); } /* * We might have stopped compacting due to need_resched() in * async compaction, or due to a fatal signal detected. In that * case do not try further zones and signal need_resched() * contention. */ if ((zone_contended == COMPACT_CONTENDED_SCHED) || fatal_signal_pending(current)) { *contended = COMPACT_CONTENDED_SCHED; goto break_loop; } continue; break_loop: /* * We might not have tried all the zones, so be conservative * and assume they are not all lock contended. */ all_zones_contended = 0; break; } /* * If at least one zone wasn't deferred or skipped, we report if all * zones that were tried were lock contended. */ if (rc > COMPACT_SKIPPED && all_zones_contended) *contended = COMPACT_CONTENDED_LOCK; return rc; } /* Compact all zones within a node */ static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc) { int zoneid; struct zone *zone; for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { zone = &pgdat->node_zones[zoneid]; if (!populated_zone(zone)) continue; cc->nr_freepages = 0; cc->nr_migratepages = 0; cc->zone = zone; INIT_LIST_HEAD(&cc->freepages); INIT_LIST_HEAD(&cc->migratepages); /* * When called via /proc/sys/vm/compact_memory * this makes sure we compact the whole zone regardless of * cached scanner positions. */ if (is_via_compact_memory(cc->order)) __reset_isolation_suitable(zone); if (is_via_compact_memory(cc->order) || !compaction_deferred(zone, cc->order)) compact_zone(zone, cc); if (cc->order > 0) { if (zone_watermark_ok(zone, cc->order, low_wmark_pages(zone), 0, 0)) compaction_defer_reset(zone, cc->order, false); } VM_BUG_ON(!list_empty(&cc->freepages)); VM_BUG_ON(!list_empty(&cc->migratepages)); } } void compact_pgdat(pg_data_t *pgdat, int order) { struct compact_control cc = { .order = order, .mode = MIGRATE_ASYNC, }; if (!order) return; __compact_pgdat(pgdat, &cc); } static void compact_node(int nid) { struct compact_control cc = { .order = -1, .mode = MIGRATE_SYNC, .ignore_skip_hint = true, }; __compact_pgdat(NODE_DATA(nid), &cc); } /* Compact all nodes in the system */ static void compact_nodes(void) { int nid; /* Flush pending updates to the LRU lists */ lru_add_drain_all(); for_each_online_node(nid) compact_node(nid); } /* The written value is actually unused, all memory is compacted */ int sysctl_compact_memory; /* This is the entry point for compacting all nodes via /proc/sys/vm */ int sysctl_compaction_handler(struct ctl_table *table, int write, void __user *buffer, size_t *length, loff_t *ppos) { if (write) compact_nodes(); return 0; } int sysctl_extfrag_handler(struct ctl_table *table, int write, void __user *buffer, size_t *length, loff_t *ppos) { proc_dointvec_minmax(table, write, buffer, length, ppos); return 0; } #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA) static ssize_t sysfs_compact_node(struct device *dev, struct device_attribute *attr, const char *buf, size_t count) { int nid = dev->id; if (nid >= 0 && nid < nr_node_ids && node_online(nid)) { /* Flush pending updates to the LRU lists */ lru_add_drain_all(); compact_node(nid); } return count; } static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node); int compaction_register_node(struct node *node) { return device_create_file(&node->dev, &dev_attr_compact); } void compaction_unregister_node(struct node *node) { return device_remove_file(&node->dev, &dev_attr_compact); } #endif /* CONFIG_SYSFS && CONFIG_NUMA */ #endif /* CONFIG_COMPACTION */