// SPDX-License-Identifier: GPL-2.0 /* * 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 #include #include #include #include #include "internal.h" #ifdef CONFIG_COMPACTION /* * Fragmentation score check interval for proactive compaction purposes. */ #define HPAGE_FRAG_CHECK_INTERVAL_MSEC (500) 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 #define CREATE_TRACE_POINTS #include #define block_start_pfn(pfn, order) round_down(pfn, 1UL << (order)) #define block_end_pfn(pfn, order) ALIGN((pfn) + 1, 1UL << (order)) /* * Page order with-respect-to which proactive compaction * calculates external fragmentation, which is used as * the "fragmentation score" of a node/zone. */ #if defined CONFIG_TRANSPARENT_HUGEPAGE #define COMPACTION_HPAGE_ORDER HPAGE_PMD_ORDER #elif defined CONFIG_HUGETLBFS #define COMPACTION_HPAGE_ORDER HUGETLB_PAGE_ORDER #else #define COMPACTION_HPAGE_ORDER (PMD_SHIFT - PAGE_SHIFT) #endif 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 split_map_pages(struct list_head *list) { unsigned int i, order, nr_pages; struct page *page, *next; LIST_HEAD(tmp_list); list_for_each_entry_safe(page, next, list, lru) { list_del(&page->lru); order = page_private(page); nr_pages = 1 << order; post_alloc_hook(page, order, __GFP_MOVABLE); if (order) split_page(page, order); for (i = 0; i < nr_pages; i++) { list_add(&page->lru, &tmp_list); page++; } } list_splice(&tmp_list, list); } #ifdef CONFIG_COMPACTION bool PageMovable(struct page *page) { const struct movable_operations *mops; VM_BUG_ON_PAGE(!PageLocked(page), page); if (!__PageMovable(page)) return false; mops = page_movable_ops(page); if (mops) return true; return false; } void __SetPageMovable(struct page *page, const struct movable_operations *mops) { VM_BUG_ON_PAGE(!PageLocked(page), page); VM_BUG_ON_PAGE((unsigned long)mops & PAGE_MAPPING_MOVABLE, page); page->mapping = (void *)((unsigned long)mops | PAGE_MAPPING_MOVABLE); } EXPORT_SYMBOL(__SetPageMovable); void __ClearPageMovable(struct page *page) { VM_BUG_ON_PAGE(!PageMovable(page), page); /* * This page still has the type of a movable page, but it's * actually not movable any more. */ page->mapping = (void *)PAGE_MAPPING_MOVABLE; } EXPORT_SYMBOL(__ClearPageMovable); /* 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_shift, compactions are skipped up * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT */ static 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 */ static 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; 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 */ static 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 = pageblock_start_pfn(zone_end_pfn(zone) - 1); } #ifdef CONFIG_SPARSEMEM /* * If the PFN falls into an offline section, return the start PFN of the * next online section. If the PFN falls into an online section or if * there is no next online section, return 0. */ static unsigned long skip_offline_sections(unsigned long start_pfn) { unsigned long start_nr = pfn_to_section_nr(start_pfn); if (online_section_nr(start_nr)) return 0; while (++start_nr <= __highest_present_section_nr) { if (online_section_nr(start_nr)) return section_nr_to_pfn(start_nr); } return 0; } /* * If the PFN falls into an offline section, return the end PFN of the * next online section in reverse. If the PFN falls into an online section * or if there is no next online section in reverse, return 0. */ static unsigned long skip_offline_sections_reverse(unsigned long start_pfn) { unsigned long start_nr = pfn_to_section_nr(start_pfn); if (!start_nr || online_section_nr(start_nr)) return 0; while (start_nr-- > 0) { if (online_section_nr(start_nr)) return section_nr_to_pfn(start_nr) + PAGES_PER_SECTION; } return 0; } #else static unsigned long skip_offline_sections(unsigned long start_pfn) { return 0; } static unsigned long skip_offline_sections_reverse(unsigned long start_pfn) { return 0; } #endif /* * Compound pages of >= pageblock_order should consistently be skipped until * released. It is always pointless to compact pages of such order (if they are * migratable), and the pageblocks they occupy cannot contain any free pages. */ static bool pageblock_skip_persistent(struct page *page) { if (!PageCompound(page)) return false; page = compound_head(page); if (compound_order(page) >= pageblock_order) return true; return false; } static bool __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source, bool check_target) { struct page *page = pfn_to_online_page(pfn); struct page *block_page; struct page *end_page; unsigned long block_pfn; if (!page) return false; if (zone != page_zone(page)) return false; if (pageblock_skip_persistent(page)) return false; /* * If skip is already cleared do no further checking once the * restart points have been set. */ if (check_source && check_target && !get_pageblock_skip(page)) return true; /* * If clearing skip for the target scanner, do not select a * non-movable pageblock as the starting point. */ if (!check_source && check_target && get_pageblock_migratetype(page) != MIGRATE_MOVABLE) return false; /* Ensure the start of the pageblock or zone is online and valid */ block_pfn = pageblock_start_pfn(pfn); block_pfn = max(block_pfn, zone->zone_start_pfn); block_page = pfn_to_online_page(block_pfn); if (block_page) { page = block_page; pfn = block_pfn; } /* Ensure the end of the pageblock or zone is online and valid */ block_pfn = pageblock_end_pfn(pfn) - 1; block_pfn = min(block_pfn, zone_end_pfn(zone) - 1); end_page = pfn_to_online_page(block_pfn); if (!end_page) return false; /* * Only clear the hint if a sample indicates there is either a * free page or an LRU page in the block. One or other condition * is necessary for the block to be a migration source/target. */ do { if (check_source && PageLRU(page)) { clear_pageblock_skip(page); return true; } if (check_target && PageBuddy(page)) { clear_pageblock_skip(page); return true; } page += (1 << PAGE_ALLOC_COSTLY_ORDER); } while (page <= end_page); return false; } /* * 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 migrate_pfn = zone->zone_start_pfn; unsigned long free_pfn = zone_end_pfn(zone) - 1; unsigned long reset_migrate = free_pfn; unsigned long reset_free = migrate_pfn; bool source_set = false; bool free_set = false; /* Only flush if a full compaction finished recently */ if (!zone->compact_blockskip_flush) return; zone->compact_blockskip_flush = false; /* * Walk the zone and update pageblock skip information. Source looks * for PageLRU while target looks for PageBuddy. When the scanner * is found, both PageBuddy and PageLRU are checked as the pageblock * is suitable as both source and target. */ for (; migrate_pfn < free_pfn; migrate_pfn += pageblock_nr_pages, free_pfn -= pageblock_nr_pages) { cond_resched(); /* Update the migrate PFN */ if (__reset_isolation_pfn(zone, migrate_pfn, true, source_set) && migrate_pfn < reset_migrate) { source_set = true; reset_migrate = migrate_pfn; zone->compact_init_migrate_pfn = reset_migrate; zone->compact_cached_migrate_pfn[0] = reset_migrate; zone->compact_cached_migrate_pfn[1] = reset_migrate; } /* Update the free PFN */ if (__reset_isolation_pfn(zone, free_pfn, free_set, true) && free_pfn > reset_free) { free_set = true; reset_free = free_pfn; zone->compact_init_free_pfn = reset_free; zone->compact_cached_free_pfn = reset_free; } } /* Leave no distance if no suitable block was reset */ if (reset_migrate >= reset_free) { zone->compact_cached_migrate_pfn[0] = migrate_pfn; zone->compact_cached_migrate_pfn[1] = migrate_pfn; zone->compact_cached_free_pfn = free_pfn; } } 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; __reset_isolation_suitable(zone); } } /* * Sets the pageblock skip bit if it was clear. Note that this is a hint as * locks are not required for read/writers. Returns true if it was already set. */ static bool test_and_set_skip(struct compact_control *cc, struct page *page) { bool skip; /* Do not update if skip hint is being ignored */ if (cc->ignore_skip_hint) return false; skip = get_pageblock_skip(page); if (!skip && !cc->no_set_skip_hint) set_pageblock_skip(page); return skip; } static void update_cached_migrate(struct compact_control *cc, unsigned long pfn) { struct zone *zone = cc->zone; /* Set for isolation rather than compaction */ if (cc->no_set_skip_hint) return; pfn = pageblock_end_pfn(pfn); /* Update where async and sync compaction should restart */ 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; } /* * 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 pfn) { struct zone *zone = cc->zone; if (cc->no_set_skip_hint) return; set_pageblock_skip(page); 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 inline bool pageblock_skip_persistent(struct page *page) { return false; } static inline void update_pageblock_skip(struct compact_control *cc, struct page *page, unsigned long pfn) { } static void update_cached_migrate(struct compact_control *cc, unsigned long pfn) { } static bool test_and_set_skip(struct compact_control *cc, struct page *page) { return false; } #endif /* CONFIG_COMPACTION */ /* * Compaction requires the taking of some coarse locks that are potentially * very heavily contended. For async compaction, trylock and record if the * lock is contended. The lock will still be acquired but compaction will * abort when the current block is finished regardless of success rate. * Sync compaction acquires the lock. * * Always returns true which makes it easier to track lock state in callers. */ static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags, struct compact_control *cc) __acquires(lock) { /* Track if the lock is contended in async mode */ if (cc->mode == MIGRATE_ASYNC && !cc->contended) { if (spin_trylock_irqsave(lock, *flags)) return true; cc->contended = true; } 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, 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. * Returns false when compaction can continue. */ 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 = true; 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, unsigned int stride, bool strict) { int nr_scanned = 0, total_isolated = 0; struct page *page; unsigned long flags = 0; bool locked = false; unsigned long blockpfn = *start_pfn; unsigned int order; /* Strict mode is for isolation, speed is secondary */ if (strict) stride = 1; page = pfn_to_page(blockpfn); /* Isolate free pages. */ for (; blockpfn < end_pfn; blockpfn += stride, page += stride) { int isolated; /* * Periodically drop the lock (if held) regardless of its * contention, to give chance to IRQs. Abort if fatal signal * pending. */ if (!(blockpfn % COMPACT_CLUSTER_MAX) && compact_unlock_should_abort(&cc->zone->lock, flags, &locked, cc)) break; nr_scanned++; /* * 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)) { const unsigned int order = compound_order(page); if (blockpfn + (1UL << order) <= end_pfn) { blockpfn += (1UL << order) - 1; page += (1UL << order) - 1; nr_scanned += (1UL << order) - 1; } goto isolate_fail; } if (!PageBuddy(page)) goto isolate_fail; /* If we already hold the lock, we can skip some rechecking. */ if (!locked) { locked = compact_lock_irqsave(&cc->zone->lock, &flags, cc); /* Recheck this is a buddy page under lock */ if (!PageBuddy(page)) goto isolate_fail; } /* Found a free page, will break it into order-0 pages */ order = buddy_order(page); isolated = __isolate_free_page(page, order); if (!isolated) break; set_page_private(page, order); nr_scanned += isolated - 1; total_isolated += isolated; cc->nr_freepages += isolated; list_add_tail(&page->lru, freelist); if (!strict && cc->nr_migratepages <= cc->nr_freepages) { blockpfn += isolated; break; } /* Advance to the end of split page */ blockpfn += isolated - 1; page += isolated - 1; continue; isolate_fail: if (strict) break; } if (locked) spin_unlock_irqrestore(&cc->zone->lock, flags); /* * 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; cc->total_free_scanned += nr_scanned; if (total_isolated) count_compact_events(COMPACTISOLATED, total_isolated); return total_isolated; } /** * isolate_freepages_range() - isolate free pages. * @cc: Compaction control structure. * @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_start_pfn, block_end_pfn; LIST_HEAD(freelist); pfn = start_pfn; block_start_pfn = pageblock_start_pfn(pfn); if (block_start_pfn < cc->zone->zone_start_pfn) block_start_pfn = cc->zone->zone_start_pfn; block_end_pfn = pageblock_end_pfn(pfn); for (; pfn < end_pfn; pfn += isolated, block_start_pfn = block_end_pfn, block_end_pfn += pageblock_nr_pages) { /* Protect pfn from changing by isolate_freepages_block */ unsigned long isolate_start_pfn = 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_start_pfn = pageblock_start_pfn(pfn); block_end_pfn = pageblock_end_pfn(pfn); } block_end_pfn = min(block_end_pfn, end_pfn); if (!pageblock_pfn_to_page(block_start_pfn, block_end_pfn, cc->zone)) break; isolated = isolate_freepages_block(cc, &isolate_start_pfn, block_end_pfn, &freelist, 0, 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). */ } /* __isolate_free_page() does not map the pages */ split_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; } /* Similar to reclaim, but different enough that they don't share logic */ static bool too_many_isolated(struct compact_control *cc) { pg_data_t *pgdat = cc->zone->zone_pgdat; bool too_many; unsigned long active, inactive, isolated; inactive = node_page_state(pgdat, NR_INACTIVE_FILE) + node_page_state(pgdat, NR_INACTIVE_ANON); active = node_page_state(pgdat, NR_ACTIVE_FILE) + node_page_state(pgdat, NR_ACTIVE_ANON); isolated = node_page_state(pgdat, NR_ISOLATED_FILE) + node_page_state(pgdat, NR_ISOLATED_ANON); /* * Allow GFP_NOFS to isolate past the limit set for regular * compaction runs. This prevents an ABBA deadlock when other * compactors have already isolated to the limit, but are * blocked on filesystem locks held by the GFP_NOFS thread. */ if (cc->gfp_mask & __GFP_FS) { inactive >>= 3; active >>= 3; } too_many = isolated > (inactive + active) / 2; if (!too_many) wake_throttle_isolated(pgdat); return too_many; } /** * 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 * @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 errno, like -EAGAIN or -EINTR in case e.g signal pending or congestion, * -ENOMEM in case we could not allocate a page, or 0. * cc->migrate_pfn will contain the next pfn to scan. * * The pages are isolated on cc->migratepages list (not required to be empty), * and cc->nr_migratepages is updated accordingly. */ static int isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, unsigned long end_pfn, isolate_mode_t mode) { pg_data_t *pgdat = cc->zone->zone_pgdat; unsigned long nr_scanned = 0, nr_isolated = 0; struct lruvec *lruvec; unsigned long flags = 0; struct lruvec *locked = NULL; struct folio *folio = NULL; struct page *page = NULL, *valid_page = NULL; struct address_space *mapping; unsigned long start_pfn = low_pfn; bool skip_on_failure = false; unsigned long next_skip_pfn = 0; bool skip_updated = false; int ret = 0; cc->migrate_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(cc))) { /* stop isolation if there are still pages not migrated */ if (cc->nr_migratepages) return -EAGAIN; /* async migration should just abort */ if (cc->mode == MIGRATE_ASYNC) return -EAGAIN; reclaim_throttle(pgdat, VMSCAN_THROTTLE_ISOLATED); if (fatal_signal_pending(current)) return -EINTR; } cond_resched(); if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) { skip_on_failure = true; next_skip_pfn = block_end_pfn(low_pfn, cc->order); } /* Time to isolate some pages for migration */ for (; low_pfn < end_pfn; low_pfn++) { if (skip_on_failure && low_pfn >= next_skip_pfn) { /* * We have isolated all migration candidates in the * previous order-aligned block, and did not skip it due * to failure. We should migrate the pages now and * hopefully succeed compaction. */ if (nr_isolated) break; /* * We failed to isolate in the previous order-aligned * block. Set the new boundary to the end of the * current block. Note we can't simply increase * next_skip_pfn by 1 << order, as low_pfn might have * been incremented by a higher number due to skipping * a compound or a high-order buddy page in the * previous loop iteration. */ next_skip_pfn = block_end_pfn(low_pfn, cc->order); } /* * Periodically drop the lock (if held) regardless of its * contention, to give chance to IRQs. Abort completely if * a fatal signal is pending. */ if (!(low_pfn % COMPACT_CLUSTER_MAX)) { if (locked) { unlock_page_lruvec_irqrestore(locked, flags); locked = NULL; } if (fatal_signal_pending(current)) { cc->contended = true; ret = -EINTR; goto fatal_pending; } cond_resched(); } nr_scanned++; page = pfn_to_page(low_pfn); /* * Check if the pageblock has already been marked skipped. * Only the first PFN is checked as the caller isolates * COMPACT_CLUSTER_MAX at a time so the second call must * not falsely conclude that the block should be skipped. */ if (!valid_page && (pageblock_aligned(low_pfn) || low_pfn == cc->zone->zone_start_pfn)) { if (!isolation_suitable(cc, page)) { low_pfn = end_pfn; folio = NULL; goto isolate_abort; } valid_page = page; } if (PageHuge(page) && cc->alloc_contig) { if (locked) { unlock_page_lruvec_irqrestore(locked, flags); locked = NULL; } ret = isolate_or_dissolve_huge_page(page, &cc->migratepages); /* * Fail isolation in case isolate_or_dissolve_huge_page() * reports an error. In case of -ENOMEM, abort right away. */ if (ret < 0) { /* Do not report -EBUSY down the chain */ if (ret == -EBUSY) ret = 0; low_pfn += compound_nr(page) - 1; nr_scanned += compound_nr(page) - 1; goto isolate_fail; } if (PageHuge(page)) { /* * Hugepage was successfully isolated and placed * on the cc->migratepages list. */ folio = page_folio(page); low_pfn += folio_nr_pages(folio) - 1; goto isolate_success_no_list; } /* * Ok, the hugepage was dissolved. Now these pages are * Buddy and cannot be re-allocated because they are * isolated. Fall-through as the check below handles * Buddy pages. */ } /* * 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 = buddy_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; nr_scanned += (1UL << freepage_order) - 1; } continue; } /* * Regardless of being on LRU, compound pages such as THP and * hugetlbfs are not to be compacted unless we are attempting * an allocation much larger than the huge page size (eg CMA). * 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) && !cc->alloc_contig) { const unsigned int order = compound_order(page); if (likely(order <= MAX_ORDER)) { low_pfn += (1UL << order) - 1; nr_scanned += (1UL << order) - 1; } goto isolate_fail; } /* * Check may be lockless but that's ok as we recheck later. * It's possible to migrate LRU and non-lru movable pages. * Skip any other type of page */ if (!PageLRU(page)) { /* * __PageMovable can return false positive so we need * to verify it under page_lock. */ if (unlikely(__PageMovable(page)) && !PageIsolated(page)) { if (locked) { unlock_page_lruvec_irqrestore(locked, flags); locked = NULL; } if (isolate_movable_page(page, mode)) { folio = page_folio(page); goto isolate_success; } } goto isolate_fail; } /* * Be careful not to clear PageLRU until after we're * sure the page is not being freed elsewhere -- the * page release code relies on it. */ folio = folio_get_nontail_page(page); if (unlikely(!folio)) goto isolate_fail; /* * 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. */ mapping = folio_mapping(folio); if (!mapping && (folio_ref_count(folio) - 1) > folio_mapcount(folio)) goto isolate_fail_put; /* * Only allow to migrate anonymous pages in GFP_NOFS context * because those do not depend on fs locks. */ if (!(cc->gfp_mask & __GFP_FS) && mapping) goto isolate_fail_put; /* Only take pages on LRU: a check now makes later tests safe */ if (!folio_test_lru(folio)) goto isolate_fail_put; /* Compaction might skip unevictable pages but CMA takes them */ if (!(mode & ISOLATE_UNEVICTABLE) && folio_test_unevictable(folio)) goto isolate_fail_put; /* * To minimise LRU disruption, the caller can indicate with * ISOLATE_ASYNC_MIGRATE that it only wants to isolate pages * it will be able to migrate without blocking - clean pages * for the most part. PageWriteback would require blocking. */ if ((mode & ISOLATE_ASYNC_MIGRATE) && folio_test_writeback(folio)) goto isolate_fail_put; if ((mode & ISOLATE_ASYNC_MIGRATE) && folio_test_dirty(folio)) { bool migrate_dirty; /* * Only folios without mappings or that have * a ->migrate_folio callback are possible to * migrate without blocking. However, we may * be racing with truncation, which can free * the mapping. Truncation holds the folio lock * until after the folio is removed from the page * cache so holding it ourselves is sufficient. */ if (!folio_trylock(folio)) goto isolate_fail_put; mapping = folio_mapping(folio); migrate_dirty = !mapping || mapping->a_ops->migrate_folio; folio_unlock(folio); if (!migrate_dirty) goto isolate_fail_put; } /* Try isolate the folio */ if (!folio_test_clear_lru(folio)) goto isolate_fail_put; lruvec = folio_lruvec(folio); /* If we already hold the lock, we can skip some rechecking */ if (lruvec != locked) { if (locked) unlock_page_lruvec_irqrestore(locked, flags); compact_lock_irqsave(&lruvec->lru_lock, &flags, cc); locked = lruvec; lruvec_memcg_debug(lruvec, folio); /* * Try get exclusive access under lock. If marked for * skip, the scan is aborted unless the current context * is a rescan to reach the end of the pageblock. */ if (!skip_updated && valid_page) { skip_updated = true; if (test_and_set_skip(cc, valid_page) && !cc->finish_pageblock) { low_pfn = end_pfn; goto isolate_abort; } } /* * folio become large since the non-locked check, * and it's on LRU. */ if (unlikely(folio_test_large(folio) && !cc->alloc_contig)) { low_pfn += folio_nr_pages(folio) - 1; nr_scanned += folio_nr_pages(folio) - 1; folio_set_lru(folio); goto isolate_fail_put; } } /* The folio is taken off the LRU */ if (folio_test_large(folio)) low_pfn += folio_nr_pages(folio) - 1; /* Successfully isolated */ lruvec_del_folio(lruvec, folio); node_stat_mod_folio(folio, NR_ISOLATED_ANON + folio_is_file_lru(folio), folio_nr_pages(folio)); isolate_success: list_add(&folio->lru, &cc->migratepages); isolate_success_no_list: cc->nr_migratepages += folio_nr_pages(folio); nr_isolated += folio_nr_pages(folio); nr_scanned += folio_nr_pages(folio) - 1; /* * Avoid isolating too much unless this block is being * fully scanned (e.g. dirty/writeback pages, parallel allocation) * or a lock is contended. For contention, isolate quickly to * potentially remove one source of contention. */ if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX && !cc->finish_pageblock && !cc->contended) { ++low_pfn; break; } continue; isolate_fail_put: /* Avoid potential deadlock in freeing page under lru_lock */ if (locked) { unlock_page_lruvec_irqrestore(locked, flags); locked = NULL; } folio_put(folio); isolate_fail: if (!skip_on_failure && ret != -ENOMEM) continue; /* * We have isolated some pages, but then failed. Release them * instead of migrating, as we cannot form the cc->order buddy * page anyway. */ if (nr_isolated) { if (locked) { unlock_page_lruvec_irqrestore(locked, flags); locked = NULL; } putback_movable_pages(&cc->migratepages); cc->nr_migratepages = 0; nr_isolated = 0; } if (low_pfn < next_skip_pfn) { low_pfn = next_skip_pfn - 1; /* * The check near the loop beginning would have updated * next_skip_pfn too, but this is a bit simpler. */ next_skip_pfn += 1UL << cc->order; } if (ret == -ENOMEM) 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; folio = NULL; isolate_abort: if (locked) unlock_page_lruvec_irqrestore(locked, flags); if (folio) { folio_set_lru(folio); folio_put(folio); } /* * Update the cached scanner pfn once the pageblock has been scanned. * Pages will either be migrated in which case there is no point * scanning in the near future or migration failed in which case the * failure reason may persist. The block is marked for skipping if * there were no pages isolated in the block or if the block is * rescanned twice in a row. */ if (low_pfn == end_pfn && (!nr_isolated || cc->finish_pageblock)) { if (!cc->no_set_skip_hint && valid_page && !skip_updated) set_pageblock_skip(valid_page); update_cached_migrate(cc, low_pfn); } trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn, nr_scanned, nr_isolated); fatal_pending: cc->total_migrate_scanned += nr_scanned; if (nr_isolated) count_compact_events(COMPACTISOLATED, nr_isolated); cc->migrate_pfn = low_pfn; return ret; } /** * 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 -EAGAIN when contented, -EINTR in case of a signal pending, -ENOMEM * in case we could not allocate a page, or 0. */ int isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn, unsigned long end_pfn) { unsigned long pfn, block_start_pfn, block_end_pfn; int ret = 0; /* Scan block by block. First and last block may be incomplete */ pfn = start_pfn; block_start_pfn = pageblock_start_pfn(pfn); if (block_start_pfn < cc->zone->zone_start_pfn) block_start_pfn = cc->zone->zone_start_pfn; block_end_pfn = pageblock_end_pfn(pfn); for (; pfn < end_pfn; pfn = block_end_pfn, block_start_pfn = block_end_pfn, block_end_pfn += pageblock_nr_pages) { block_end_pfn = min(block_end_pfn, end_pfn); if (!pageblock_pfn_to_page(block_start_pfn, block_end_pfn, cc->zone)) continue; ret = isolate_migratepages_block(cc, pfn, block_end_pfn, ISOLATE_UNEVICTABLE); if (ret) break; if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX) break; } return ret; } #endif /* CONFIG_COMPACTION || CONFIG_CMA */ #ifdef CONFIG_COMPACTION static bool suitable_migration_source(struct compact_control *cc, struct page *page) { int block_mt; if (pageblock_skip_persistent(page)) return false; if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction) return true; block_mt = get_pageblock_migratetype(page); if (cc->migratetype == MIGRATE_MOVABLE) return is_migrate_movable(block_mt); else return block_mt == cc->migratetype; } /* Returns true if the page is within a block suitable for migration to */ static bool suitable_migration_target(struct compact_control *cc, 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 (buddy_order_unsafe(page) >= pageblock_order) return false; } if (cc->ignore_block_suitable) return true; /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */ if (is_migrate_movable(get_pageblock_migratetype(page))) return true; /* Otherwise skip the block */ return false; } static inline unsigned int freelist_scan_limit(struct compact_control *cc) { unsigned short shift = BITS_PER_LONG - 1; return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1; } /* * 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); } /* * Used when scanning for a suitable migration target which scans freelists * in reverse. Reorders the list such as the unscanned pages are scanned * first on the next iteration of the free scanner */ static void move_freelist_head(struct list_head *freelist, struct page *freepage) { LIST_HEAD(sublist); if (!list_is_first(&freepage->buddy_list, freelist)) { list_cut_before(&sublist, freelist, &freepage->buddy_list); list_splice_tail(&sublist, freelist); } } /* * Similar to move_freelist_head except used by the migration scanner * when scanning forward. It's possible for these list operations to * move against each other if they search the free list exactly in * lockstep. */ static void move_freelist_tail(struct list_head *freelist, struct page *freepage) { LIST_HEAD(sublist); if (!list_is_last(&freepage->buddy_list, freelist)) { list_cut_position(&sublist, freelist, &freepage->buddy_list); list_splice_tail(&sublist, freelist); } } static void fast_isolate_around(struct compact_control *cc, unsigned long pfn) { unsigned long start_pfn, end_pfn; struct page *page; /* Do not search around if there are enough pages already */ if (cc->nr_freepages >= cc->nr_migratepages) return; /* Minimise scanning during async compaction */ if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC) return; /* Pageblock boundaries */ start_pfn = max(pageblock_start_pfn(pfn), cc->zone->zone_start_pfn); end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone)); page = pageblock_pfn_to_page(start_pfn, end_pfn, cc->zone); if (!page) return; isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false); /* Skip this pageblock in the future as it's full or nearly full */ if (start_pfn == end_pfn && !cc->no_set_skip_hint) set_pageblock_skip(page); } /* Search orders in round-robin fashion */ static int next_search_order(struct compact_control *cc, int order) { order--; if (order < 0) order = cc->order - 1; /* Search wrapped around? */ if (order == cc->search_order) { cc->search_order--; if (cc->search_order < 0) cc->search_order = cc->order - 1; return -1; } return order; } static void fast_isolate_freepages(struct compact_control *cc) { unsigned int limit = max(1U, freelist_scan_limit(cc) >> 1); unsigned int nr_scanned = 0, total_isolated = 0; unsigned long low_pfn, min_pfn, highest = 0; unsigned long nr_isolated = 0; unsigned long distance; struct page *page = NULL; bool scan_start = false; int order; /* Full compaction passes in a negative order */ if (cc->order <= 0) return; /* * If starting the scan, use a deeper search and use the highest * PFN found if a suitable one is not found. */ if (cc->free_pfn >= cc->zone->compact_init_free_pfn) { limit = pageblock_nr_pages >> 1; scan_start = true; } /* * Preferred point is in the top quarter of the scan space but take * a pfn from the top half if the search is problematic. */ distance = (cc->free_pfn - cc->migrate_pfn); low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2)); min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1)); if (WARN_ON_ONCE(min_pfn > low_pfn)) low_pfn = min_pfn; /* * Search starts from the last successful isolation order or the next * order to search after a previous failure */ cc->search_order = min_t(unsigned int, cc->order - 1, cc->search_order); for (order = cc->search_order; !page && order >= 0; order = next_search_order(cc, order)) { struct free_area *area = &cc->zone->free_area[order]; struct list_head *freelist; struct page *freepage; unsigned long flags; unsigned int order_scanned = 0; unsigned long high_pfn = 0; if (!area->nr_free) continue; spin_lock_irqsave(&cc->zone->lock, flags); freelist = &area->free_list[MIGRATE_MOVABLE]; list_for_each_entry_reverse(freepage, freelist, buddy_list) { unsigned long pfn; order_scanned++; nr_scanned++; pfn = page_to_pfn(freepage); if (pfn >= highest) highest = max(pageblock_start_pfn(pfn), cc->zone->zone_start_pfn); if (pfn >= low_pfn) { cc->fast_search_fail = 0; cc->search_order = order; page = freepage; break; } if (pfn >= min_pfn && pfn > high_pfn) { high_pfn = pfn; /* Shorten the scan if a candidate is found */ limit >>= 1; } if (order_scanned >= limit) break; } /* Use a maximum candidate pfn if a preferred one was not found */ if (!page && high_pfn) { page = pfn_to_page(high_pfn); /* Update freepage for the list reorder below */ freepage = page; } /* Reorder to so a future search skips recent pages */ move_freelist_head(freelist, freepage); /* Isolate the page if available */ if (page) { if (__isolate_free_page(page, order)) { set_page_private(page, order); nr_isolated = 1 << order; nr_scanned += nr_isolated - 1; total_isolated += nr_isolated; cc->nr_freepages += nr_isolated; list_add_tail(&page->lru, &cc->freepages); count_compact_events(COMPACTISOLATED, nr_isolated); } else { /* If isolation fails, abort the search */ order = cc->search_order + 1; page = NULL; } } spin_unlock_irqrestore(&cc->zone->lock, flags); /* Skip fast search if enough freepages isolated */ if (cc->nr_freepages >= cc->nr_migratepages) break; /* * Smaller scan on next order so the total scan is related * to freelist_scan_limit. */ if (order_scanned >= limit) limit = max(1U, limit >> 1); } trace_mm_compaction_fast_isolate_freepages(min_pfn, cc->free_pfn, nr_scanned, total_isolated); if (!page) { cc->fast_search_fail++; if (scan_start) { /* * Use the highest PFN found above min. If one was * not found, be pessimistic for direct compaction * and use the min mark. */ if (highest >= min_pfn) { page = pfn_to_page(highest); cc->free_pfn = highest; } else { if (cc->direct_compaction && pfn_valid(min_pfn)) { page = pageblock_pfn_to_page(min_pfn, min(pageblock_end_pfn(min_pfn), zone_end_pfn(cc->zone)), cc->zone); cc->free_pfn = min_pfn; } } } } if (highest && highest >= cc->zone->compact_cached_free_pfn) { highest -= pageblock_nr_pages; cc->zone->compact_cached_free_pfn = highest; } cc->total_free_scanned += nr_scanned; if (!page) return; low_pfn = page_to_pfn(page); fast_isolate_around(cc, low_pfn); } /* * 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; unsigned int stride; /* Try a small search of the free lists for a candidate */ fast_isolate_freepages(cc); if (cc->nr_freepages) goto splitmap; /* * 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 * 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 = pageblock_start_pfn(isolate_start_pfn); block_end_pfn = min(block_start_pfn + pageblock_nr_pages, zone_end_pfn(zone)); low_pfn = pageblock_end_pfn(cc->migrate_pfn); stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1; /* * 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) { unsigned long nr_isolated; /* * This can iterate a massively long zone without finding any * suitable migration targets, so periodically check resched. */ if (!(block_start_pfn % (COMPACT_CLUSTER_MAX * pageblock_nr_pages))) cond_resched(); page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn, zone); if (!page) { unsigned long next_pfn; next_pfn = skip_offline_sections_reverse(block_start_pfn); if (next_pfn) block_start_pfn = max(next_pfn, low_pfn); continue; } /* Check the block is suitable for migration */ if (!suitable_migration_target(cc, page)) continue; /* If isolation recently failed, do not retry */ if (!isolation_suitable(cc, page)) continue; /* Found a block suitable for isolating free pages from. */ nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn, block_end_pfn, freelist, stride, false); /* Update the skip hint if the full pageblock was scanned */ if (isolate_start_pfn == block_end_pfn) update_pageblock_skip(cc, page, block_start_pfn - pageblock_nr_pages); /* Are enough freepages isolated? */ if (cc->nr_freepages >= cc->nr_migratepages) { if (isolate_start_pfn >= block_end_pfn) { /* * Restart at previous pageblock if more * freepages can be isolated next time. */ isolate_start_pfn = block_start_pfn - pageblock_nr_pages; } break; } else if (isolate_start_pfn < block_end_pfn) { /* * If isolation failed early, do not continue * needlessly. */ break; } /* Adjust stride depending on isolation */ if (nr_isolated) { stride = 1; continue; } stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1); } /* * 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; splitmap: /* __isolate_free_page() does not map the pages */ split_map_pages(freelist); } /* * This is a migrate-callback that "allocates" freepages by taking pages * from the isolated freelists in the block we are migrating to. */ static struct folio *compaction_alloc(struct folio *src, unsigned long data) { struct compact_control *cc = (struct compact_control *)data; struct folio *dst; if (list_empty(&cc->freepages)) { isolate_freepages(cc); if (list_empty(&cc->freepages)) return NULL; } dst = list_entry(cc->freepages.next, struct folio, lru); list_del(&dst->lru); cc->nr_freepages--; return dst; } /* * 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 folio *dst, unsigned long data) { struct compact_control *cc = (struct compact_control *)data; list_add(&dst->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. */ static int sysctl_compact_unevictable_allowed __read_mostly = CONFIG_COMPACT_UNEVICTABLE_DEFAULT; /* * Tunable for proactive compaction. It determines how * aggressively the kernel should compact memory in the * background. It takes values in the range [0, 100]. */ static unsigned int __read_mostly sysctl_compaction_proactiveness = 20; static int sysctl_extfrag_threshold = 500; static int __read_mostly sysctl_compact_memory; static inline void update_fast_start_pfn(struct compact_control *cc, unsigned long pfn) { if (cc->fast_start_pfn == ULONG_MAX) return; if (!cc->fast_start_pfn) cc->fast_start_pfn = pfn; cc->fast_start_pfn = min(cc->fast_start_pfn, pfn); } static inline unsigned long reinit_migrate_pfn(struct compact_control *cc) { if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX) return cc->migrate_pfn; cc->migrate_pfn = cc->fast_start_pfn; cc->fast_start_pfn = ULONG_MAX; return cc->migrate_pfn; } /* * Briefly search the free lists for a migration source that already has * some free pages to reduce the number of pages that need migration * before a pageblock is free. */ static unsigned long fast_find_migrateblock(struct compact_control *cc) { unsigned int limit = freelist_scan_limit(cc); unsigned int nr_scanned = 0; unsigned long distance; unsigned long pfn = cc->migrate_pfn; unsigned long high_pfn; int order; bool found_block = false; /* Skip hints are relied on to avoid repeats on the fast search */ if (cc->ignore_skip_hint) return pfn; /* * If the pageblock should be finished then do not select a different * pageblock. */ if (cc->finish_pageblock) return pfn; /* * If the migrate_pfn is not at the start of a zone or the start * of a pageblock then assume this is a continuation of a previous * scan restarted due to COMPACT_CLUSTER_MAX. */ if (pfn != cc->zone->zone_start_pfn && pfn != pageblock_start_pfn(pfn)) return pfn; /* * For smaller orders, just linearly scan as the number of pages * to migrate should be relatively small and does not necessarily * justify freeing up a large block for a small allocation. */ if (cc->order <= PAGE_ALLOC_COSTLY_ORDER) return pfn; /* * Only allow kcompactd and direct requests for movable pages to * quickly clear out a MOVABLE pageblock for allocation. This * reduces the risk that a large movable pageblock is freed for * an unmovable/reclaimable small allocation. */ if (cc->direct_compaction && cc->migratetype != MIGRATE_MOVABLE) return pfn; /* * When starting the migration scanner, pick any pageblock within the * first half of the search space. Otherwise try and pick a pageblock * within the first eighth to reduce the chances that a migration * target later becomes a source. */ distance = (cc->free_pfn - cc->migrate_pfn) >> 1; if (cc->migrate_pfn != cc->zone->zone_start_pfn) distance >>= 2; high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance); for (order = cc->order - 1; order >= PAGE_ALLOC_COSTLY_ORDER && !found_block && nr_scanned < limit; order--) { struct free_area *area = &cc->zone->free_area[order]; struct list_head *freelist; unsigned long flags; struct page *freepage; if (!area->nr_free) continue; spin_lock_irqsave(&cc->zone->lock, flags); freelist = &area->free_list[MIGRATE_MOVABLE]; list_for_each_entry(freepage, freelist, buddy_list) { unsigned long free_pfn; if (nr_scanned++ >= limit) { move_freelist_tail(freelist, freepage); break; } free_pfn = page_to_pfn(freepage); if (free_pfn < high_pfn) { /* * Avoid if skipped recently. Ideally it would * move to the tail but even safe iteration of * the list assumes an entry is deleted, not * reordered. */ if (get_pageblock_skip(freepage)) continue; /* Reorder to so a future search skips recent pages */ move_freelist_tail(freelist, freepage); update_fast_start_pfn(cc, free_pfn); pfn = pageblock_start_pfn(free_pfn); if (pfn < cc->zone->zone_start_pfn) pfn = cc->zone->zone_start_pfn; cc->fast_search_fail = 0; found_block = true; break; } } spin_unlock_irqrestore(&cc->zone->lock, flags); } cc->total_migrate_scanned += nr_scanned; /* * If fast scanning failed then use a cached entry for a page block * that had free pages as the basis for starting a linear scan. */ if (!found_block) { cc->fast_search_fail++; pfn = reinit_migrate_pfn(cc); } return pfn; } /* * 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 compact_control *cc) { unsigned long block_start_pfn; unsigned long block_end_pfn; unsigned long low_pfn; struct page *page; const isolate_mode_t isolate_mode = (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) | (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0); bool fast_find_block; /* * Start at where we last stopped, or beginning of the zone as * initialized by compact_zone(). The first failure will use * the lowest PFN as the starting point for linear scanning. */ low_pfn = fast_find_migrateblock(cc); block_start_pfn = pageblock_start_pfn(low_pfn); if (block_start_pfn < cc->zone->zone_start_pfn) block_start_pfn = cc->zone->zone_start_pfn; /* * fast_find_migrateblock() has already ensured the pageblock is not * set with a skipped flag, so to avoid the isolation_suitable check * below again, check whether the fast search was successful. */ fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail; /* Only scan within a pageblock boundary */ block_end_pfn = pageblock_end_pfn(low_pfn); /* * Iterate over whole pageblocks until we find the first suitable. * Do not cross the free scanner. */ for (; block_end_pfn <= cc->free_pfn; fast_find_block = false, cc->migrate_pfn = low_pfn = block_end_pfn, block_start_pfn = block_end_pfn, block_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. */ if (!(low_pfn % (COMPACT_CLUSTER_MAX * pageblock_nr_pages))) cond_resched(); page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn, cc->zone); if (!page) { unsigned long next_pfn; next_pfn = skip_offline_sections(block_start_pfn); if (next_pfn) block_end_pfn = min(next_pfn, cc->free_pfn); continue; } /* * If isolation recently failed, do not retry. Only check the * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock * to be visited multiple times. Assume skip was checked * before making it "skip" so other compaction instances do * not scan the same block. */ if ((pageblock_aligned(low_pfn) || low_pfn == cc->zone->zone_start_pfn) && !fast_find_block && !isolation_suitable(cc, page)) continue; /* * For async direct compaction, only scan the pageblocks of the * same migratetype without huge pages. Async direct compaction * is optimistic to see if the minimum amount of work satisfies * the allocation. The cached PFN is updated as it's possible * that all remaining blocks between source and target are * unsuitable and the compaction scanners fail to meet. */ if (!suitable_migration_source(cc, page)) { update_cached_migrate(cc, block_end_pfn); continue; } /* Perform the isolation */ if (isolate_migratepages_block(cc, low_pfn, block_end_pfn, isolate_mode)) return ISOLATE_ABORT; /* * Either we isolated something and proceed with migration. Or * we failed and compact_zone should decide if we should * continue or not. */ break; } return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE; } /* * order == -1 is expected when compacting proactively via * 1. /proc/sys/vm/compact_memory * 2. /sys/devices/system/node/nodex/compact * 3. /proc/sys/vm/compaction_proactiveness */ static inline bool is_via_compact_memory(int order) { return order == -1; } /* * Determine whether kswapd is (or recently was!) running on this node. * * pgdat_kswapd_lock() pins pgdat->kswapd, so a concurrent kswapd_stop() can't * zero it. */ static bool kswapd_is_running(pg_data_t *pgdat) { bool running; pgdat_kswapd_lock(pgdat); running = pgdat->kswapd && task_is_running(pgdat->kswapd); pgdat_kswapd_unlock(pgdat); return running; } /* * A zone's fragmentation score is the external fragmentation wrt to the * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100]. */ static unsigned int fragmentation_score_zone(struct zone *zone) { return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER); } /* * A weighted zone's fragmentation score is the external fragmentation * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It * returns a value in the range [0, 100]. * * The scaling factor ensures that proactive compaction focuses on larger * zones like ZONE_NORMAL, rather than smaller, specialized zones like * ZONE_DMA32. For smaller zones, the score value remains close to zero, * and thus never exceeds the high threshold for proactive compaction. */ static unsigned int fragmentation_score_zone_weighted(struct zone *zone) { unsigned long score; score = zone->present_pages * fragmentation_score_zone(zone); return div64_ul(score, zone->zone_pgdat->node_present_pages + 1); } /* * The per-node proactive (background) compaction process is started by its * corresponding kcompactd thread when the node's fragmentation score * exceeds the high threshold. The compaction process remains active till * the node's score falls below the low threshold, or one of the back-off * conditions is met. */ static unsigned int fragmentation_score_node(pg_data_t *pgdat) { unsigned int score = 0; int zoneid; for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { struct zone *zone; zone = &pgdat->node_zones[zoneid]; if (!populated_zone(zone)) continue; score += fragmentation_score_zone_weighted(zone); } return score; } static unsigned int fragmentation_score_wmark(bool low) { unsigned int wmark_low; /* * Cap the low watermark to avoid excessive compaction * activity in case a user sets the proactiveness tunable * close to 100 (maximum). */ wmark_low = max(100U - sysctl_compaction_proactiveness, 5U); return low ? wmark_low : min(wmark_low + 10, 100U); } static bool should_proactive_compact_node(pg_data_t *pgdat) { int wmark_high; if (!sysctl_compaction_proactiveness || kswapd_is_running(pgdat)) return false; wmark_high = fragmentation_score_wmark(false); return fragmentation_score_node(pgdat) > wmark_high; } static enum compact_result __compact_finished(struct compact_control *cc) { unsigned int order; const int migratetype = cc->migratetype; int ret; /* Compaction run completes if the migrate and free scanner meet */ if (compact_scanners_met(cc)) { /* Let the next compaction start anew. */ reset_cached_positions(cc->zone); /* * Mark that the PG_migrate_skip information should be cleared * by kswapd when it goes to sleep. kcompactd does not set the * flag itself as the decision to be clear should be directly * based on an allocation request. */ if (cc->direct_compaction) cc->zone->compact_blockskip_flush = true; if (cc->whole_zone) return COMPACT_COMPLETE; else return COMPACT_PARTIAL_SKIPPED; } if (cc->proactive_compaction) { int score, wmark_low; pg_data_t *pgdat; pgdat = cc->zone->zone_pgdat; if (kswapd_is_running(pgdat)) return COMPACT_PARTIAL_SKIPPED; score = fragmentation_score_zone(cc->zone); wmark_low = fragmentation_score_wmark(true); if (score > wmark_low) ret = COMPACT_CONTINUE; else ret = COMPACT_SUCCESS; goto out; } if (is_via_compact_memory(cc->order)) return COMPACT_CONTINUE; /* * Always finish scanning a pageblock to reduce the possibility of * fallbacks in the future. This is particularly important when * migration source is unmovable/reclaimable but it's not worth * special casing. */ if (!pageblock_aligned(cc->migrate_pfn)) return COMPACT_CONTINUE; /* Direct compactor: Is a suitable page free? */ ret = COMPACT_NO_SUITABLE_PAGE; for (order = cc->order; order <= MAX_ORDER; order++) { struct free_area *area = &cc->zone->free_area[order]; bool can_steal; /* Job done if page is free of the right migratetype */ if (!free_area_empty(area, migratetype)) return COMPACT_SUCCESS; #ifdef CONFIG_CMA /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */ if (migratetype == MIGRATE_MOVABLE && !free_area_empty(area, MIGRATE_CMA)) return COMPACT_SUCCESS; #endif /* * Job done if allocation would steal freepages from * other migratetype buddy lists. */ if (find_suitable_fallback(area, order, migratetype, true, &can_steal) != -1) /* * Movable pages are OK in any pageblock. If we are * stealing for a non-movable allocation, make sure * we finish compacting the current pageblock first * (which is assured by the above migrate_pfn align * check) so it is as free as possible and we won't * have to steal another one soon. */ return COMPACT_SUCCESS; } out: if (cc->contended || fatal_signal_pending(current)) ret = COMPACT_CONTENDED; return ret; } static enum compact_result compact_finished(struct compact_control *cc) { int ret; ret = __compact_finished(cc); trace_mm_compaction_finished(cc->zone, cc->order, ret); if (ret == COMPACT_NO_SUITABLE_PAGE) ret = COMPACT_CONTINUE; return ret; } static bool __compaction_suitable(struct zone *zone, int order, int highest_zoneidx, unsigned long wmark_target) { unsigned long watermark; /* * Watermarks for order-0 must be met for compaction to be able to * isolate free pages for migration targets. This means that the * watermark and alloc_flags have to match, or be more pessimistic than * the check in __isolate_free_page(). We don't use the direct * compactor's alloc_flags, as they are not relevant for freepage * isolation. We however do use the direct compactor's highest_zoneidx * to skip over zones where lowmem reserves would prevent allocation * even if compaction succeeds. * For costly orders, we require low watermark instead of min for * compaction to proceed to increase its chances. * ALLOC_CMA is used, as pages in CMA pageblocks are considered * suitable migration targets */ watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ? low_wmark_pages(zone) : min_wmark_pages(zone); watermark += compact_gap(order); return __zone_watermark_ok(zone, 0, watermark, highest_zoneidx, ALLOC_CMA, wmark_target); } /* * compaction_suitable: Is this suitable to run compaction on this zone now? */ bool compaction_suitable(struct zone *zone, int order, int highest_zoneidx) { enum compact_result compact_result; bool suitable; suitable = __compaction_suitable(zone, order, highest_zoneidx, zone_page_state(zone, NR_FREE_PAGES)); /* * 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. Also * ignore fragindex for non-costly orders where the alternative to * a successful reclaim/compaction is OOM. Fragindex and the * vm.extfrag_threshold sysctl is meant as a heuristic to prevent * excessive compaction for costly orders, but it should not be at the * expense of system stability. */ if (suitable) { compact_result = COMPACT_CONTINUE; if (order > PAGE_ALLOC_COSTLY_ORDER) { int fragindex = fragmentation_index(zone, order); if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold) { suitable = false; compact_result = COMPACT_NOT_SUITABLE_ZONE; } } } else { compact_result = COMPACT_SKIPPED; } trace_mm_compaction_suitable(zone, order, compact_result); return suitable; } bool compaction_zonelist_suitable(struct alloc_context *ac, int order, int alloc_flags) { struct zone *zone; struct zoneref *z; /* * Make sure at least one zone would pass __compaction_suitable if we continue * retrying the reclaim. */ for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->highest_zoneidx, ac->nodemask) { unsigned long available; /* * Do not consider all the reclaimable memory because we do not * want to trash just for a single high order allocation which * is even not guaranteed to appear even if __compaction_suitable * is happy about the watermark check. */ available = zone_reclaimable_pages(zone) / order; available += zone_page_state_snapshot(zone, NR_FREE_PAGES); if (__compaction_suitable(zone, order, ac->highest_zoneidx, available)) return true; } return false; } /* * Should we do compaction for target allocation order. * Return COMPACT_SUCCESS if allocation for target order can be already * satisfied * Return COMPACT_SKIPPED if compaction for target order is likely to fail * Return COMPACT_CONTINUE if compaction for target order should be ran */ static enum compact_result compaction_suit_allocation_order(struct zone *zone, unsigned int order, int highest_zoneidx, unsigned int alloc_flags) { unsigned long watermark; watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK); if (zone_watermark_ok(zone, order, watermark, highest_zoneidx, alloc_flags)) return COMPACT_SUCCESS; if (!compaction_suitable(zone, order, highest_zoneidx)) return COMPACT_SKIPPED; return COMPACT_CONTINUE; } static enum compact_result compact_zone(struct compact_control *cc, struct capture_control *capc) { enum compact_result ret; unsigned long start_pfn = cc->zone->zone_start_pfn; unsigned long end_pfn = zone_end_pfn(cc->zone); unsigned long last_migrated_pfn; const bool sync = cc->mode != MIGRATE_ASYNC; bool update_cached; unsigned int nr_succeeded = 0; /* * These counters track activities during zone compaction. Initialize * them before compacting a new zone. */ cc->total_migrate_scanned = 0; cc->total_free_scanned = 0; cc->nr_migratepages = 0; cc->nr_freepages = 0; INIT_LIST_HEAD(&cc->freepages); INIT_LIST_HEAD(&cc->migratepages); cc->migratetype = gfp_migratetype(cc->gfp_mask); if (!is_via_compact_memory(cc->order)) { ret = compaction_suit_allocation_order(cc->zone, cc->order, cc->highest_zoneidx, cc->alloc_flags); if (ret != COMPACT_CONTINUE) return ret; } /* * Clear pageblock skip if there were failures recently and compaction * is about to be retried after being deferred. */ if (compaction_restarting(cc->zone, cc->order)) __reset_isolation_suitable(cc->zone); /* * Setup to move all movable pages to the end of the zone. Used cached * information on where the scanners should start (unless we explicitly * want to compact the whole zone), but check that it is initialised * by ensuring the values are within zone boundaries. */ cc->fast_start_pfn = 0; if (cc->whole_zone) { cc->migrate_pfn = start_pfn; cc->free_pfn = pageblock_start_pfn(end_pfn - 1); } else { cc->migrate_pfn = cc->zone->compact_cached_migrate_pfn[sync]; cc->free_pfn = cc->zone->compact_cached_free_pfn; if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) { cc->free_pfn = pageblock_start_pfn(end_pfn - 1); cc->zone->compact_cached_free_pfn = cc->free_pfn; } if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) { cc->migrate_pfn = start_pfn; cc->zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn; cc->zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn; } if (cc->migrate_pfn <= cc->zone->compact_init_migrate_pfn) cc->whole_zone = true; } last_migrated_pfn = 0; /* * Migrate has separate cached PFNs for ASYNC and SYNC* migration on * the basis that some migrations will fail in ASYNC mode. However, * if the cached PFNs match and pageblocks are skipped due to having * no isolation candidates, then the sync state does not matter. * Until a pageblock with isolation candidates is found, keep the * cached PFNs in sync to avoid revisiting the same blocks. */ update_cached = !sync && cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1]; trace_mm_compaction_begin(cc, start_pfn, end_pfn, sync); /* lru_add_drain_all could be expensive with involving other CPUs */ lru_add_drain(); while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) { int err; unsigned long iteration_start_pfn = cc->migrate_pfn; /* * Avoid multiple rescans of the same pageblock which can * happen if a page cannot be isolated (dirty/writeback in * async mode) or if the migrated pages are being allocated * before the pageblock is cleared. The first rescan will * capture the entire pageblock for migration. If it fails, * it'll be marked skip and scanning will proceed as normal. */ cc->finish_pageblock = false; if (pageblock_start_pfn(last_migrated_pfn) == pageblock_start_pfn(iteration_start_pfn)) { cc->finish_pageblock = true; } rescan: switch (isolate_migratepages(cc)) { case ISOLATE_ABORT: ret = COMPACT_CONTENDED; putback_movable_pages(&cc->migratepages); cc->nr_migratepages = 0; goto out; case ISOLATE_NONE: if (update_cached) { cc->zone->compact_cached_migrate_pfn[1] = cc->zone->compact_cached_migrate_pfn[0]; } /* * 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: update_cached = false; last_migrated_pfn = max(cc->zone->zone_start_pfn, pageblock_start_pfn(cc->migrate_pfn - 1)); } err = migrate_pages(&cc->migratepages, compaction_alloc, compaction_free, (unsigned long)cc, cc->mode, MR_COMPACTION, &nr_succeeded); trace_mm_compaction_migratepages(cc, nr_succeeded); /* 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_CONTENDED; goto out; } /* * If an ASYNC or SYNC_LIGHT fails to migrate a page * within the pageblock_order-aligned block and * fast_find_migrateblock may be used then scan the * remainder of the pageblock. This will mark the * pageblock "skip" to avoid rescanning in the near * future. This will isolate more pages than necessary * for the request but avoid loops due to * fast_find_migrateblock revisiting blocks that were * recently partially scanned. */ if (!pageblock_aligned(cc->migrate_pfn) && !cc->ignore_skip_hint && !cc->finish_pageblock && (cc->mode < MIGRATE_SYNC)) { cc->finish_pageblock = true; /* * Draining pcplists does not help THP if * any page failed to migrate. Even after * drain, the pageblock will not be free. */ if (cc->order == COMPACTION_HPAGE_ORDER) last_migrated_pfn = 0; goto rescan; } } /* Stop if a page has been captured */ if (capc && capc->page) { ret = COMPACT_SUCCESS; break; } 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 && last_migrated_pfn) { unsigned long current_block_start = block_start_pfn(cc->migrate_pfn, cc->order); if (last_migrated_pfn < current_block_start) { lru_add_drain_cpu_zone(cc->zone); /* No more flushing until we migrate again */ 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_start_pfn(free_pfn); /* * Only go back, not forward. The cached pfn might have been * already reset to zone end in compact_finished() */ if (free_pfn > cc->zone->compact_cached_free_pfn) cc->zone->compact_cached_free_pfn = free_pfn; } count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned); count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned); trace_mm_compaction_end(cc, start_pfn, end_pfn, sync, ret); VM_BUG_ON(!list_empty(&cc->freepages)); VM_BUG_ON(!list_empty(&cc->migratepages)); return ret; } static enum compact_result compact_zone_order(struct zone *zone, int order, gfp_t gfp_mask, enum compact_priority prio, unsigned int alloc_flags, int highest_zoneidx, struct page **capture) { enum compact_result ret; struct compact_control cc = { .order = order, .search_order = order, .gfp_mask = gfp_mask, .zone = zone, .mode = (prio == COMPACT_PRIO_ASYNC) ? MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT, .alloc_flags = alloc_flags, .highest_zoneidx = highest_zoneidx, .direct_compaction = true, .whole_zone = (prio == MIN_COMPACT_PRIORITY), .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY), .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY) }; struct capture_control capc = { .cc = &cc, .page = NULL, }; /* * Make sure the structs are really initialized before we expose the * capture control, in case we are interrupted and the interrupt handler * frees a page. */ barrier(); WRITE_ONCE(current->capture_control, &capc); ret = compact_zone(&cc, &capc); /* * Make sure we hide capture control first before we read the captured * page pointer, otherwise an interrupt could free and capture a page * and we would leak it. */ WRITE_ONCE(current->capture_control, NULL); *capture = READ_ONCE(capc.page); /* * Technically, it is also possible that compaction is skipped but * the page is still captured out of luck(IRQ came and freed the page). * Returning COMPACT_SUCCESS in such cases helps in properly accounting * the COMPACT[STALL|FAIL] when compaction is skipped. */ if (*capture) ret = COMPACT_SUCCESS; return ret; } /** * 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 * @prio: Determines how hard direct compaction should try to succeed * @capture: Pointer to free page created by compaction will be stored here * * This is the main entry point for direct page compaction. */ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order, unsigned int alloc_flags, const struct alloc_context *ac, enum compact_priority prio, struct page **capture) { struct zoneref *z; struct zone *zone; enum compact_result rc = COMPACT_SKIPPED; if (!gfp_compaction_allowed(gfp_mask)) return COMPACT_SKIPPED; trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio); /* Compact each zone in the list */ for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->highest_zoneidx, ac->nodemask) { enum compact_result status; if (prio > MIN_COMPACT_PRIORITY && compaction_deferred(zone, order)) { rc = max_t(enum compact_result, COMPACT_DEFERRED, rc); continue; } status = compact_zone_order(zone, order, gfp_mask, prio, alloc_flags, ac->highest_zoneidx, capture); rc = max(status, rc); /* The allocation should succeed, stop compacting */ if (status == COMPACT_SUCCESS) { /* * 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); break; } if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE || status == COMPACT_PARTIAL_SKIPPED)) /* * 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 */ if ((prio == COMPACT_PRIO_ASYNC && need_resched()) || fatal_signal_pending(current)) break; } return rc; } /* * Compact all zones within a node till each zone's fragmentation score * reaches within proactive compaction thresholds (as determined by the * proactiveness tunable). * * It is possible that the function returns before reaching score targets * due to various back-off conditions, such as, contention on per-node or * per-zone locks. */ static void proactive_compact_node(pg_data_t *pgdat) { int zoneid; struct zone *zone; struct compact_control cc = { .order = -1, .mode = MIGRATE_SYNC_LIGHT, .ignore_skip_hint = true, .whole_zone = true, .gfp_mask = GFP_KERNEL, .proactive_compaction = true, }; for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { zone = &pgdat->node_zones[zoneid]; if (!populated_zone(zone)) continue; cc.zone = zone; compact_zone(&cc, NULL); count_compact_events(KCOMPACTD_MIGRATE_SCANNED, cc.total_migrate_scanned); count_compact_events(KCOMPACTD_FREE_SCANNED, cc.total_free_scanned); } } /* Compact all zones within a node */ static void compact_node(int nid) { pg_data_t *pgdat = NODE_DATA(nid); int zoneid; struct zone *zone; struct compact_control cc = { .order = -1, .mode = MIGRATE_SYNC, .ignore_skip_hint = true, .whole_zone = true, .gfp_mask = GFP_KERNEL, }; for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { zone = &pgdat->node_zones[zoneid]; if (!populated_zone(zone)) continue; cc.zone = zone; compact_zone(&cc, NULL); } } /* 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); } static int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write, void *buffer, size_t *length, loff_t *ppos) { int rc, nid; rc = proc_dointvec_minmax(table, write, buffer, length, ppos); if (rc) return rc; if (write && sysctl_compaction_proactiveness) { for_each_online_node(nid) { pg_data_t *pgdat = NODE_DATA(nid); if (pgdat->proactive_compact_trigger) continue; pgdat->proactive_compact_trigger = true; trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, -1, pgdat->nr_zones - 1); wake_up_interruptible(&pgdat->kcompactd_wait); } } return 0; } /* * This is the entry point for compacting all nodes via * /proc/sys/vm/compact_memory */ static int sysctl_compaction_handler(struct ctl_table *table, int write, void *buffer, size_t *length, loff_t *ppos) { int ret; ret = proc_dointvec(table, write, buffer, length, ppos); if (ret) return ret; if (sysctl_compact_memory != 1) return -EINVAL; if (write) compact_nodes(); return 0; } #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA) static ssize_t compact_store(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_WO(compact); int compaction_register_node(struct node *node) { return device_create_file(&node->dev, &dev_attr_compact); } void compaction_unregister_node(struct node *node) { device_remove_file(&node->dev, &dev_attr_compact); } #endif /* CONFIG_SYSFS && CONFIG_NUMA */ static inline bool kcompactd_work_requested(pg_data_t *pgdat) { return pgdat->kcompactd_max_order > 0 || kthread_should_stop() || pgdat->proactive_compact_trigger; } static bool kcompactd_node_suitable(pg_data_t *pgdat) { int zoneid; struct zone *zone; enum zone_type highest_zoneidx = pgdat->kcompactd_highest_zoneidx; enum compact_result ret; for (zoneid = 0; zoneid <= highest_zoneidx; zoneid++) { zone = &pgdat->node_zones[zoneid]; if (!populated_zone(zone)) continue; ret = compaction_suit_allocation_order(zone, pgdat->kcompactd_max_order, highest_zoneidx, ALLOC_WMARK_MIN); if (ret == COMPACT_CONTINUE) return true; } return false; } static void kcompactd_do_work(pg_data_t *pgdat) { /* * With no special task, compact all zones so that a page of requested * order is allocatable. */ int zoneid; struct zone *zone; struct compact_control cc = { .order = pgdat->kcompactd_max_order, .search_order = pgdat->kcompactd_max_order, .highest_zoneidx = pgdat->kcompactd_highest_zoneidx, .mode = MIGRATE_SYNC_LIGHT, .ignore_skip_hint = false, .gfp_mask = GFP_KERNEL, }; enum compact_result ret; trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order, cc.highest_zoneidx); count_compact_event(KCOMPACTD_WAKE); for (zoneid = 0; zoneid <= cc.highest_zoneidx; zoneid++) { int status; zone = &pgdat->node_zones[zoneid]; if (!populated_zone(zone)) continue; if (compaction_deferred(zone, cc.order)) continue; ret = compaction_suit_allocation_order(zone, cc.order, zoneid, ALLOC_WMARK_MIN); if (ret != COMPACT_CONTINUE) continue; if (kthread_should_stop()) return; cc.zone = zone; status = compact_zone(&cc, NULL); if (status == COMPACT_SUCCESS) { compaction_defer_reset(zone, cc.order, false); } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) { /* * Buddy pages may become stranded on pcps that could * otherwise coalesce on the zone's free area for * order >= cc.order. This is ratelimited by the * upcoming deferral. */ drain_all_pages(zone); /* * We use sync migration mode here, so we defer like * sync direct compaction does. */ defer_compaction(zone, cc.order); } count_compact_events(KCOMPACTD_MIGRATE_SCANNED, cc.total_migrate_scanned); count_compact_events(KCOMPACTD_FREE_SCANNED, cc.total_free_scanned); } /* * Regardless of success, we are done until woken up next. But remember * the requested order/highest_zoneidx in case it was higher/tighter * than our current ones */ if (pgdat->kcompactd_max_order <= cc.order) pgdat->kcompactd_max_order = 0; if (pgdat->kcompactd_highest_zoneidx >= cc.highest_zoneidx) pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1; } void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx) { if (!order) return; if (pgdat->kcompactd_max_order < order) pgdat->kcompactd_max_order = order; if (pgdat->kcompactd_highest_zoneidx > highest_zoneidx) pgdat->kcompactd_highest_zoneidx = highest_zoneidx; /* * Pairs with implicit barrier in wait_event_freezable() * such that wakeups are not missed. */ if (!wq_has_sleeper(&pgdat->kcompactd_wait)) return; if (!kcompactd_node_suitable(pgdat)) return; trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order, highest_zoneidx); wake_up_interruptible(&pgdat->kcompactd_wait); } /* * The background compaction daemon, started as a kernel thread * from the init process. */ static int kcompactd(void *p) { pg_data_t *pgdat = (pg_data_t *)p; struct task_struct *tsk = current; long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC); long timeout = default_timeout; const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id); if (!cpumask_empty(cpumask)) set_cpus_allowed_ptr(tsk, cpumask); set_freezable(); pgdat->kcompactd_max_order = 0; pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1; while (!kthread_should_stop()) { unsigned long pflags; /* * Avoid the unnecessary wakeup for proactive compaction * when it is disabled. */ if (!sysctl_compaction_proactiveness) timeout = MAX_SCHEDULE_TIMEOUT; trace_mm_compaction_kcompactd_sleep(pgdat->node_id); if (wait_event_freezable_timeout(pgdat->kcompactd_wait, kcompactd_work_requested(pgdat), timeout) && !pgdat->proactive_compact_trigger) { psi_memstall_enter(&pflags); kcompactd_do_work(pgdat); psi_memstall_leave(&pflags); /* * Reset the timeout value. The defer timeout from * proactive compaction is lost here but that is fine * as the condition of the zone changing substantionally * then carrying on with the previous defer interval is * not useful. */ timeout = default_timeout; continue; } /* * Start the proactive work with default timeout. Based * on the fragmentation score, this timeout is updated. */ timeout = default_timeout; if (should_proactive_compact_node(pgdat)) { unsigned int prev_score, score; prev_score = fragmentation_score_node(pgdat); proactive_compact_node(pgdat); score = fragmentation_score_node(pgdat); /* * Defer proactive compaction if the fragmentation * score did not go down i.e. no progress made. */ if (unlikely(score >= prev_score)) timeout = default_timeout << COMPACT_MAX_DEFER_SHIFT; } if (unlikely(pgdat->proactive_compact_trigger)) pgdat->proactive_compact_trigger = false; } return 0; } /* * This kcompactd start function will be called by init and node-hot-add. * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added. */ void __meminit kcompactd_run(int nid) { pg_data_t *pgdat = NODE_DATA(nid); if (pgdat->kcompactd) return; pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid); if (IS_ERR(pgdat->kcompactd)) { pr_err("Failed to start kcompactd on node %d\n", nid); pgdat->kcompactd = NULL; } } /* * Called by memory hotplug when all memory in a node is offlined. Caller must * be holding mem_hotplug_begin/done(). */ void __meminit kcompactd_stop(int nid) { struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd; if (kcompactd) { kthread_stop(kcompactd); NODE_DATA(nid)->kcompactd = NULL; } } /* * It's optimal to keep kcompactd on the same CPUs as their memory, but * not required for correctness. So if the last cpu in a node goes * away, we get changed to run anywhere: as the first one comes back, * restore their cpu bindings. */ static int kcompactd_cpu_online(unsigned int cpu) { int nid; for_each_node_state(nid, N_MEMORY) { pg_data_t *pgdat = NODE_DATA(nid); const struct cpumask *mask; mask = cpumask_of_node(pgdat->node_id); if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids) /* One of our CPUs online: restore mask */ if (pgdat->kcompactd) set_cpus_allowed_ptr(pgdat->kcompactd, mask); } return 0; } static int proc_dointvec_minmax_warn_RT_change(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos) { int ret, old; if (!IS_ENABLED(CONFIG_PREEMPT_RT) || !write) return proc_dointvec_minmax(table, write, buffer, lenp, ppos); old = *(int *)table->data; ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); if (ret) return ret; if (old != *(int *)table->data) pr_warn_once("sysctl attribute %s changed by %s[%d]\n", table->procname, current->comm, task_pid_nr(current)); return ret; } static struct ctl_table vm_compaction[] = { { .procname = "compact_memory", .data = &sysctl_compact_memory, .maxlen = sizeof(int), .mode = 0200, .proc_handler = sysctl_compaction_handler, }, { .procname = "compaction_proactiveness", .data = &sysctl_compaction_proactiveness, .maxlen = sizeof(sysctl_compaction_proactiveness), .mode = 0644, .proc_handler = compaction_proactiveness_sysctl_handler, .extra1 = SYSCTL_ZERO, .extra2 = SYSCTL_ONE_HUNDRED, }, { .procname = "extfrag_threshold", .data = &sysctl_extfrag_threshold, .maxlen = sizeof(int), .mode = 0644, .proc_handler = proc_dointvec_minmax, .extra1 = SYSCTL_ZERO, .extra2 = SYSCTL_ONE_THOUSAND, }, { .procname = "compact_unevictable_allowed", .data = &sysctl_compact_unevictable_allowed, .maxlen = sizeof(int), .mode = 0644, .proc_handler = proc_dointvec_minmax_warn_RT_change, .extra1 = SYSCTL_ZERO, .extra2 = SYSCTL_ONE, }, { } }; static int __init kcompactd_init(void) { int nid; int ret; ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "mm/compaction:online", kcompactd_cpu_online, NULL); if (ret < 0) { pr_err("kcompactd: failed to register hotplug callbacks.\n"); return ret; } for_each_node_state(nid, N_MEMORY) kcompactd_run(nid); register_sysctl_init("vm", vm_compaction); return 0; } subsys_initcall(kcompactd_init) #endif /* CONFIG_COMPACTION */