/* * linux/mm/vmscan.c * * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds * * Swap reorganised 29.12.95, Stephen Tweedie. * kswapd added: 7.1.96 sct * Removed kswapd_ctl limits, and swap out as many pages as needed * to bring the system back to freepages.high: 2.4.97, Rik van Riel. * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com). * Multiqueue VM started 5.8.00, Rik van Riel. */ #include #include #include #include #include #include #include #include #include #include #include #include #include /* for try_to_release_page(), buffer_heads_over_limit */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "internal.h" #define CREATE_TRACE_POINTS #include /* * reclaim_mode determines how the inactive list is shrunk * RECLAIM_MODE_SINGLE: Reclaim only order-0 pages * RECLAIM_MODE_ASYNC: Do not block * RECLAIM_MODE_SYNC: Allow blocking e.g. call wait_on_page_writeback * RECLAIM_MODE_LUMPYRECLAIM: For high-order allocations, take a reference * page from the LRU and reclaim all pages within a * naturally aligned range * RECLAIM_MODE_COMPACTION: For high-order allocations, reclaim a number of * order-0 pages and then compact the zone */ typedef unsigned __bitwise__ reclaim_mode_t; #define RECLAIM_MODE_SINGLE ((__force reclaim_mode_t)0x01u) #define RECLAIM_MODE_ASYNC ((__force reclaim_mode_t)0x02u) #define RECLAIM_MODE_SYNC ((__force reclaim_mode_t)0x04u) #define RECLAIM_MODE_LUMPYRECLAIM ((__force reclaim_mode_t)0x08u) #define RECLAIM_MODE_COMPACTION ((__force reclaim_mode_t)0x10u) struct scan_control { /* Incremented by the number of inactive pages that were scanned */ unsigned long nr_scanned; /* Number of pages freed so far during a call to shrink_zones() */ unsigned long nr_reclaimed; /* How many pages shrink_list() should reclaim */ unsigned long nr_to_reclaim; unsigned long hibernation_mode; /* This context's GFP mask */ gfp_t gfp_mask; int may_writepage; /* Can mapped pages be reclaimed? */ int may_unmap; /* Can pages be swapped as part of reclaim? */ int may_swap; int swappiness; int order; /* * Intend to reclaim enough continuous memory rather than reclaim * enough amount of memory. i.e, mode for high order allocation. */ reclaim_mode_t reclaim_mode; /* Which cgroup do we reclaim from */ struct mem_cgroup *mem_cgroup; /* * Nodemask of nodes allowed by the caller. If NULL, all nodes * are scanned. */ nodemask_t *nodemask; }; #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru)) #ifdef ARCH_HAS_PREFETCH #define prefetch_prev_lru_page(_page, _base, _field) \ do { \ if ((_page)->lru.prev != _base) { \ struct page *prev; \ \ prev = lru_to_page(&(_page->lru)); \ prefetch(&prev->_field); \ } \ } while (0) #else #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0) #endif #ifdef ARCH_HAS_PREFETCHW #define prefetchw_prev_lru_page(_page, _base, _field) \ do { \ if ((_page)->lru.prev != _base) { \ struct page *prev; \ \ prev = lru_to_page(&(_page->lru)); \ prefetchw(&prev->_field); \ } \ } while (0) #else #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0) #endif /* * From 0 .. 100. Higher means more swappy. */ int vm_swappiness = 60; long vm_total_pages; /* The total number of pages which the VM controls */ static LIST_HEAD(shrinker_list); static DECLARE_RWSEM(shrinker_rwsem); #ifdef CONFIG_CGROUP_MEM_RES_CTLR #define scanning_global_lru(sc) (!(sc)->mem_cgroup) #else #define scanning_global_lru(sc) (1) #endif static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone, struct scan_control *sc) { if (!scanning_global_lru(sc)) return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone); return &zone->reclaim_stat; } static unsigned long zone_nr_lru_pages(struct zone *zone, struct scan_control *sc, enum lru_list lru) { if (!scanning_global_lru(sc)) return mem_cgroup_zone_nr_lru_pages(sc->mem_cgroup, zone, lru); return zone_page_state(zone, NR_LRU_BASE + lru); } /* * Add a shrinker callback to be called from the vm */ void register_shrinker(struct shrinker *shrinker) { shrinker->nr = 0; down_write(&shrinker_rwsem); list_add_tail(&shrinker->list, &shrinker_list); up_write(&shrinker_rwsem); } EXPORT_SYMBOL(register_shrinker); /* * Remove one */ void unregister_shrinker(struct shrinker *shrinker) { down_write(&shrinker_rwsem); list_del(&shrinker->list); up_write(&shrinker_rwsem); } EXPORT_SYMBOL(unregister_shrinker); static inline int do_shrinker_shrink(struct shrinker *shrinker, struct shrink_control *sc, unsigned long nr_to_scan) { sc->nr_to_scan = nr_to_scan; return (*shrinker->shrink)(shrinker, sc); } #define SHRINK_BATCH 128 /* * Call the shrink functions to age shrinkable caches * * Here we assume it costs one seek to replace a lru page and that it also * takes a seek to recreate a cache object. With this in mind we age equal * percentages of the lru and ageable caches. This should balance the seeks * generated by these structures. * * If the vm encountered mapped pages on the LRU it increase the pressure on * slab to avoid swapping. * * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits. * * `lru_pages' represents the number of on-LRU pages in all the zones which * are eligible for the caller's allocation attempt. It is used for balancing * slab reclaim versus page reclaim. * * Returns the number of slab objects which we shrunk. */ unsigned long shrink_slab(struct shrink_control *shrink, unsigned long nr_pages_scanned, unsigned long lru_pages) { struct shrinker *shrinker; unsigned long ret = 0; if (nr_pages_scanned == 0) nr_pages_scanned = SWAP_CLUSTER_MAX; if (!down_read_trylock(&shrinker_rwsem)) { /* Assume we'll be able to shrink next time */ ret = 1; goto out; } list_for_each_entry(shrinker, &shrinker_list, list) { unsigned long long delta; unsigned long total_scan; unsigned long max_pass; int shrink_ret = 0; long nr; long new_nr; /* * copy the current shrinker scan count into a local variable * and zero it so that other concurrent shrinker invocations * don't also do this scanning work. */ do { nr = shrinker->nr; } while (cmpxchg(&shrinker->nr, nr, 0) != nr); total_scan = nr; max_pass = do_shrinker_shrink(shrinker, shrink, 0); delta = (4 * nr_pages_scanned) / shrinker->seeks; delta *= max_pass; do_div(delta, lru_pages + 1); total_scan += delta; if (total_scan < 0) { printk(KERN_ERR "shrink_slab: %pF negative objects to " "delete nr=%ld\n", shrinker->shrink, total_scan); total_scan = max_pass; } /* * We need to avoid excessive windup on filesystem shrinkers * due to large numbers of GFP_NOFS allocations causing the * shrinkers to return -1 all the time. This results in a large * nr being built up so when a shrink that can do some work * comes along it empties the entire cache due to nr >>> * max_pass. This is bad for sustaining a working set in * memory. * * Hence only allow the shrinker to scan the entire cache when * a large delta change is calculated directly. */ if (delta < max_pass / 4) total_scan = min(total_scan, max_pass / 2); /* * Avoid risking looping forever due to too large nr value: * never try to free more than twice the estimate number of * freeable entries. */ if (total_scan > max_pass * 2) total_scan = max_pass * 2; trace_mm_shrink_slab_start(shrinker, shrink, nr, nr_pages_scanned, lru_pages, max_pass, delta, total_scan); while (total_scan >= SHRINK_BATCH) { long this_scan = SHRINK_BATCH; int nr_before; nr_before = do_shrinker_shrink(shrinker, shrink, 0); shrink_ret = do_shrinker_shrink(shrinker, shrink, this_scan); if (shrink_ret == -1) break; if (shrink_ret < nr_before) ret += nr_before - shrink_ret; count_vm_events(SLABS_SCANNED, this_scan); total_scan -= this_scan; cond_resched(); } /* * move the unused scan count back into the shrinker in a * manner that handles concurrent updates. If we exhausted the * scan, there is no need to do an update. */ do { nr = shrinker->nr; new_nr = total_scan + nr; if (total_scan <= 0) break; } while (cmpxchg(&shrinker->nr, nr, new_nr) != nr); trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr); } up_read(&shrinker_rwsem); out: cond_resched(); return ret; } static void set_reclaim_mode(int priority, struct scan_control *sc, bool sync) { reclaim_mode_t syncmode = sync ? RECLAIM_MODE_SYNC : RECLAIM_MODE_ASYNC; /* * Initially assume we are entering either lumpy reclaim or * reclaim/compaction.Depending on the order, we will either set the * sync mode or just reclaim order-0 pages later. */ if (COMPACTION_BUILD) sc->reclaim_mode = RECLAIM_MODE_COMPACTION; else sc->reclaim_mode = RECLAIM_MODE_LUMPYRECLAIM; /* * Avoid using lumpy reclaim or reclaim/compaction if possible by * restricting when its set to either costly allocations or when * under memory pressure */ if (sc->order > PAGE_ALLOC_COSTLY_ORDER) sc->reclaim_mode |= syncmode; else if (sc->order && priority < DEF_PRIORITY - 2) sc->reclaim_mode |= syncmode; else sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC; } static void reset_reclaim_mode(struct scan_control *sc) { sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC; } static inline int is_page_cache_freeable(struct page *page) { /* * A freeable page cache page is referenced only by the caller * that isolated the page, the page cache radix tree and * optional buffer heads at page->private. */ return page_count(page) - page_has_private(page) == 2; } static int may_write_to_queue(struct backing_dev_info *bdi, struct scan_control *sc) { if (current->flags & PF_SWAPWRITE) return 1; if (!bdi_write_congested(bdi)) return 1; if (bdi == current->backing_dev_info) return 1; /* lumpy reclaim for hugepage often need a lot of write */ if (sc->order > PAGE_ALLOC_COSTLY_ORDER) return 1; return 0; } /* * We detected a synchronous write error writing a page out. Probably * -ENOSPC. We need to propagate that into the address_space for a subsequent * fsync(), msync() or close(). * * The tricky part is that after writepage we cannot touch the mapping: nothing * prevents it from being freed up. But we have a ref on the page and once * that page is locked, the mapping is pinned. * * We're allowed to run sleeping lock_page() here because we know the caller has * __GFP_FS. */ static void handle_write_error(struct address_space *mapping, struct page *page, int error) { lock_page(page); if (page_mapping(page) == mapping) mapping_set_error(mapping, error); unlock_page(page); } /* possible outcome of pageout() */ typedef enum { /* failed to write page out, page is locked */ PAGE_KEEP, /* move page to the active list, page is locked */ PAGE_ACTIVATE, /* page has been sent to the disk successfully, page is unlocked */ PAGE_SUCCESS, /* page is clean and locked */ PAGE_CLEAN, } pageout_t; /* * pageout is called by shrink_page_list() for each dirty page. * Calls ->writepage(). */ static pageout_t pageout(struct page *page, struct address_space *mapping, struct scan_control *sc) { /* * If the page is dirty, only perform writeback if that write * will be non-blocking. To prevent this allocation from being * stalled by pagecache activity. But note that there may be * stalls if we need to run get_block(). We could test * PagePrivate for that. * * If this process is currently in __generic_file_aio_write() against * this page's queue, we can perform writeback even if that * will block. * * If the page is swapcache, write it back even if that would * block, for some throttling. This happens by accident, because * swap_backing_dev_info is bust: it doesn't reflect the * congestion state of the swapdevs. Easy to fix, if needed. */ if (!is_page_cache_freeable(page)) return PAGE_KEEP; if (!mapping) { /* * Some data journaling orphaned pages can have * page->mapping == NULL while being dirty with clean buffers. */ if (page_has_private(page)) { if (try_to_free_buffers(page)) { ClearPageDirty(page); printk("%s: orphaned page\n", __func__); return PAGE_CLEAN; } } return PAGE_KEEP; } if (mapping->a_ops->writepage == NULL) return PAGE_ACTIVATE; if (!may_write_to_queue(mapping->backing_dev_info, sc)) return PAGE_KEEP; if (clear_page_dirty_for_io(page)) { int res; struct writeback_control wbc = { .sync_mode = WB_SYNC_NONE, .nr_to_write = SWAP_CLUSTER_MAX, .range_start = 0, .range_end = LLONG_MAX, .for_reclaim = 1, }; SetPageReclaim(page); res = mapping->a_ops->writepage(page, &wbc); if (res < 0) handle_write_error(mapping, page, res); if (res == AOP_WRITEPAGE_ACTIVATE) { ClearPageReclaim(page); return PAGE_ACTIVATE; } /* * Wait on writeback if requested to. This happens when * direct reclaiming a large contiguous area and the * first attempt to free a range of pages fails. */ if (PageWriteback(page) && (sc->reclaim_mode & RECLAIM_MODE_SYNC)) wait_on_page_writeback(page); if (!PageWriteback(page)) { /* synchronous write or broken a_ops? */ ClearPageReclaim(page); } trace_mm_vmscan_writepage(page, trace_reclaim_flags(page, sc->reclaim_mode)); inc_zone_page_state(page, NR_VMSCAN_WRITE); return PAGE_SUCCESS; } return PAGE_CLEAN; } /* * Same as remove_mapping, but if the page is removed from the mapping, it * gets returned with a refcount of 0. */ static int __remove_mapping(struct address_space *mapping, struct page *page) { BUG_ON(!PageLocked(page)); BUG_ON(mapping != page_mapping(page)); spin_lock_irq(&mapping->tree_lock); /* * The non racy check for a busy page. * * Must be careful with the order of the tests. When someone has * a ref to the page, it may be possible that they dirty it then * drop the reference. So if PageDirty is tested before page_count * here, then the following race may occur: * * get_user_pages(&page); * [user mapping goes away] * write_to(page); * !PageDirty(page) [good] * SetPageDirty(page); * put_page(page); * !page_count(page) [good, discard it] * * [oops, our write_to data is lost] * * Reversing the order of the tests ensures such a situation cannot * escape unnoticed. The smp_rmb is needed to ensure the page->flags * load is not satisfied before that of page->_count. * * Note that if SetPageDirty is always performed via set_page_dirty, * and thus under tree_lock, then this ordering is not required. */ if (!page_freeze_refs(page, 2)) goto cannot_free; /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */ if (unlikely(PageDirty(page))) { page_unfreeze_refs(page, 2); goto cannot_free; } if (PageSwapCache(page)) { swp_entry_t swap = { .val = page_private(page) }; __delete_from_swap_cache(page); spin_unlock_irq(&mapping->tree_lock); swapcache_free(swap, page); } else { void (*freepage)(struct page *); freepage = mapping->a_ops->freepage; __delete_from_page_cache(page); spin_unlock_irq(&mapping->tree_lock); mem_cgroup_uncharge_cache_page(page); if (freepage != NULL) freepage(page); } return 1; cannot_free: spin_unlock_irq(&mapping->tree_lock); return 0; } /* * Attempt to detach a locked page from its ->mapping. If it is dirty or if * someone else has a ref on the page, abort and return 0. If it was * successfully detached, return 1. Assumes the caller has a single ref on * this page. */ int remove_mapping(struct address_space *mapping, struct page *page) { if (__remove_mapping(mapping, page)) { /* * Unfreezing the refcount with 1 rather than 2 effectively * drops the pagecache ref for us without requiring another * atomic operation. */ page_unfreeze_refs(page, 1); return 1; } return 0; } /** * putback_lru_page - put previously isolated page onto appropriate LRU list * @page: page to be put back to appropriate lru list * * Add previously isolated @page to appropriate LRU list. * Page may still be unevictable for other reasons. * * lru_lock must not be held, interrupts must be enabled. */ void putback_lru_page(struct page *page) { int lru; int active = !!TestClearPageActive(page); int was_unevictable = PageUnevictable(page); VM_BUG_ON(PageLRU(page)); redo: ClearPageUnevictable(page); if (page_evictable(page, NULL)) { /* * For evictable pages, we can use the cache. * In event of a race, worst case is we end up with an * unevictable page on [in]active list. * We know how to handle that. */ lru = active + page_lru_base_type(page); lru_cache_add_lru(page, lru); } else { /* * Put unevictable pages directly on zone's unevictable * list. */ lru = LRU_UNEVICTABLE; add_page_to_unevictable_list(page); /* * When racing with an mlock clearing (page is * unlocked), make sure that if the other thread does * not observe our setting of PG_lru and fails * isolation, we see PG_mlocked cleared below and move * the page back to the evictable list. * * The other side is TestClearPageMlocked(). */ smp_mb(); } /* * page's status can change while we move it among lru. If an evictable * page is on unevictable list, it never be freed. To avoid that, * check after we added it to the list, again. */ if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) { if (!isolate_lru_page(page)) { put_page(page); goto redo; } /* This means someone else dropped this page from LRU * So, it will be freed or putback to LRU again. There is * nothing to do here. */ } if (was_unevictable && lru != LRU_UNEVICTABLE) count_vm_event(UNEVICTABLE_PGRESCUED); else if (!was_unevictable && lru == LRU_UNEVICTABLE) count_vm_event(UNEVICTABLE_PGCULLED); put_page(page); /* drop ref from isolate */ } enum page_references { PAGEREF_RECLAIM, PAGEREF_RECLAIM_CLEAN, PAGEREF_KEEP, PAGEREF_ACTIVATE, }; static enum page_references page_check_references(struct page *page, struct scan_control *sc) { int referenced_ptes, referenced_page; unsigned long vm_flags; referenced_ptes = page_referenced(page, 1, sc->mem_cgroup, &vm_flags); referenced_page = TestClearPageReferenced(page); /* Lumpy reclaim - ignore references */ if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM) return PAGEREF_RECLAIM; /* * Mlock lost the isolation race with us. Let try_to_unmap() * move the page to the unevictable list. */ if (vm_flags & VM_LOCKED) return PAGEREF_RECLAIM; if (referenced_ptes) { if (PageSwapBacked(page)) return PAGEREF_ACTIVATE; /* * All mapped pages start out with page table * references from the instantiating fault, so we need * to look twice if a mapped file page is used more * than once. * * Mark it and spare it for another trip around the * inactive list. Another page table reference will * lead to its activation. * * Note: the mark is set for activated pages as well * so that recently deactivated but used pages are * quickly recovered. */ SetPageReferenced(page); if (referenced_page || referenced_ptes > 1) return PAGEREF_ACTIVATE; /* * Activate file-backed executable pages after first usage. */ if (vm_flags & VM_EXEC) return PAGEREF_ACTIVATE; return PAGEREF_KEEP; } /* Reclaim if clean, defer dirty pages to writeback */ if (referenced_page && !PageSwapBacked(page)) return PAGEREF_RECLAIM_CLEAN; return PAGEREF_RECLAIM; } static noinline_for_stack void free_page_list(struct list_head *free_pages) { struct pagevec freed_pvec; struct page *page, *tmp; pagevec_init(&freed_pvec, 1); list_for_each_entry_safe(page, tmp, free_pages, lru) { list_del(&page->lru); if (!pagevec_add(&freed_pvec, page)) { __pagevec_free(&freed_pvec); pagevec_reinit(&freed_pvec); } } pagevec_free(&freed_pvec); } /* * shrink_page_list() returns the number of reclaimed pages */ static unsigned long shrink_page_list(struct list_head *page_list, struct zone *zone, struct scan_control *sc) { LIST_HEAD(ret_pages); LIST_HEAD(free_pages); int pgactivate = 0; unsigned long nr_dirty = 0; unsigned long nr_congested = 0; unsigned long nr_reclaimed = 0; cond_resched(); while (!list_empty(page_list)) { enum page_references references; struct address_space *mapping; struct page *page; int may_enter_fs; cond_resched(); page = lru_to_page(page_list); list_del(&page->lru); if (!trylock_page(page)) goto keep; VM_BUG_ON(PageActive(page)); VM_BUG_ON(page_zone(page) != zone); sc->nr_scanned++; if (unlikely(!page_evictable(page, NULL))) goto cull_mlocked; if (!sc->may_unmap && page_mapped(page)) goto keep_locked; /* Double the slab pressure for mapped and swapcache pages */ if (page_mapped(page) || PageSwapCache(page)) sc->nr_scanned++; may_enter_fs = (sc->gfp_mask & __GFP_FS) || (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); if (PageWriteback(page)) { /* * Synchronous reclaim is performed in two passes, * first an asynchronous pass over the list to * start parallel writeback, and a second synchronous * pass to wait for the IO to complete. Wait here * for any page for which writeback has already * started. */ if ((sc->reclaim_mode & RECLAIM_MODE_SYNC) && may_enter_fs) wait_on_page_writeback(page); else { unlock_page(page); goto keep_lumpy; } } references = page_check_references(page, sc); switch (references) { case PAGEREF_ACTIVATE: goto activate_locked; case PAGEREF_KEEP: goto keep_locked; case PAGEREF_RECLAIM: case PAGEREF_RECLAIM_CLEAN: ; /* try to reclaim the page below */ } /* * Anonymous process memory has backing store? * Try to allocate it some swap space here. */ if (PageAnon(page) && !PageSwapCache(page)) { if (!(sc->gfp_mask & __GFP_IO)) goto keep_locked; if (!add_to_swap(page)) goto activate_locked; may_enter_fs = 1; } mapping = page_mapping(page); /* * The page is mapped into the page tables of one or more * processes. Try to unmap it here. */ if (page_mapped(page) && mapping) { switch (try_to_unmap(page, TTU_UNMAP)) { case SWAP_FAIL: goto activate_locked; case SWAP_AGAIN: goto keep_locked; case SWAP_MLOCK: goto cull_mlocked; case SWAP_SUCCESS: ; /* try to free the page below */ } } if (PageDirty(page)) { nr_dirty++; if (references == PAGEREF_RECLAIM_CLEAN) goto keep_locked; if (!may_enter_fs) goto keep_locked; if (!sc->may_writepage) goto keep_locked; /* Page is dirty, try to write it out here */ switch (pageout(page, mapping, sc)) { case PAGE_KEEP: nr_congested++; goto keep_locked; case PAGE_ACTIVATE: goto activate_locked; case PAGE_SUCCESS: if (PageWriteback(page)) goto keep_lumpy; if (PageDirty(page)) goto keep; /* * A synchronous write - probably a ramdisk. Go * ahead and try to reclaim the page. */ if (!trylock_page(page)) goto keep; if (PageDirty(page) || PageWriteback(page)) goto keep_locked; mapping = page_mapping(page); case PAGE_CLEAN: ; /* try to free the page below */ } } /* * If the page has buffers, try to free the buffer mappings * associated with this page. If we succeed we try to free * the page as well. * * We do this even if the page is PageDirty(). * try_to_release_page() does not perform I/O, but it is * possible for a page to have PageDirty set, but it is actually * clean (all its buffers are clean). This happens if the * buffers were written out directly, with submit_bh(). ext3 * will do this, as well as the blockdev mapping. * try_to_release_page() will discover that cleanness and will * drop the buffers and mark the page clean - it can be freed. * * Rarely, pages can have buffers and no ->mapping. These are * the pages which were not successfully invalidated in * truncate_complete_page(). We try to drop those buffers here * and if that worked, and the page is no longer mapped into * process address space (page_count == 1) it can be freed. * Otherwise, leave the page on the LRU so it is swappable. */ if (page_has_private(page)) { if (!try_to_release_page(page, sc->gfp_mask)) goto activate_locked; if (!mapping && page_count(page) == 1) { unlock_page(page); if (put_page_testzero(page)) goto free_it; else { /* * rare race with speculative reference. * the speculative reference will free * this page shortly, so we may * increment nr_reclaimed here (and * leave it off the LRU). */ nr_reclaimed++; continue; } } } if (!mapping || !__remove_mapping(mapping, page)) goto keep_locked; /* * At this point, we have no other references and there is * no way to pick any more up (removed from LRU, removed * from pagecache). Can use non-atomic bitops now (and * we obviously don't have to worry about waking up a process * waiting on the page lock, because there are no references. */ __clear_page_locked(page); free_it: nr_reclaimed++; /* * Is there need to periodically free_page_list? It would * appear not as the counts should be low */ list_add(&page->lru, &free_pages); continue; cull_mlocked: if (PageSwapCache(page)) try_to_free_swap(page); unlock_page(page); putback_lru_page(page); reset_reclaim_mode(sc); continue; activate_locked: /* Not a candidate for swapping, so reclaim swap space. */ if (PageSwapCache(page) && vm_swap_full()) try_to_free_swap(page); VM_BUG_ON(PageActive(page)); SetPageActive(page); pgactivate++; keep_locked: unlock_page(page); keep: reset_reclaim_mode(sc); keep_lumpy: list_add(&page->lru, &ret_pages); VM_BUG_ON(PageLRU(page) || PageUnevictable(page)); } /* * Tag a zone as congested if all the dirty pages encountered were * backed by a congested BDI. In this case, reclaimers should just * back off and wait for congestion to clear because further reclaim * will encounter the same problem */ if (nr_dirty && nr_dirty == nr_congested && scanning_global_lru(sc)) zone_set_flag(zone, ZONE_CONGESTED); free_page_list(&free_pages); list_splice(&ret_pages, page_list); count_vm_events(PGACTIVATE, pgactivate); return nr_reclaimed; } /* * Attempt to remove the specified page from its LRU. Only take this page * if it is of the appropriate PageActive status. Pages which are being * freed elsewhere are also ignored. * * page: page to consider * mode: one of the LRU isolation modes defined above * * returns 0 on success, -ve errno on failure. */ int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file) { bool all_lru_mode; int ret = -EINVAL; /* Only take pages on the LRU. */ if (!PageLRU(page)) return ret; all_lru_mode = (mode & (ISOLATE_ACTIVE|ISOLATE_INACTIVE)) == (ISOLATE_ACTIVE|ISOLATE_INACTIVE); /* * When checking the active state, we need to be sure we are * dealing with comparible boolean values. Take the logical not * of each. */ if (!all_lru_mode && !PageActive(page) != !(mode & ISOLATE_ACTIVE)) return ret; if (!all_lru_mode && !!page_is_file_cache(page) != file) return ret; /* * When this function is being called for lumpy reclaim, we * initially look into all LRU pages, active, inactive and * unevictable; only give shrink_page_list evictable pages. */ if (PageUnevictable(page)) return ret; ret = -EBUSY; /* * To minimise LRU disruption, the caller can indicate that it only * wants to isolate pages it will be able to operate on without * blocking - clean pages for the most part. * * ISOLATE_CLEAN means that only clean pages should be isolated. This * is used by reclaim when it is cannot write to backing storage * * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages * that it is possible to migrate without blocking */ if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) { /* All the caller can do on PageWriteback is block */ if (PageWriteback(page)) return ret; if (PageDirty(page)) { struct address_space *mapping; /* ISOLATE_CLEAN means only clean pages */ if (mode & ISOLATE_CLEAN) return ret; /* * Only pages without mappings or that have a * ->migratepage callback are possible to migrate * without blocking */ mapping = page_mapping(page); if (mapping && !mapping->a_ops->migratepage) return ret; } } if ((mode & ISOLATE_UNMAPPED) && page_mapped(page)) return ret; if (likely(get_page_unless_zero(page))) { /* * 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. */ ClearPageLRU(page); ret = 0; } return ret; } /* * zone->lru_lock is heavily contended. Some of the functions that * shrink the lists perform better by taking out a batch of pages * and working on them outside the LRU lock. * * For pagecache intensive workloads, this function is the hottest * spot in the kernel (apart from copy_*_user functions). * * Appropriate locks must be held before calling this function. * * @nr_to_scan: The number of pages to look through on the list. * @src: The LRU list to pull pages off. * @dst: The temp list to put pages on to. * @scanned: The number of pages that were scanned. * @order: The caller's attempted allocation order * @mode: One of the LRU isolation modes * @file: True [1] if isolating file [!anon] pages * * returns how many pages were moved onto *@dst. */ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, struct list_head *src, struct list_head *dst, unsigned long *scanned, int order, isolate_mode_t mode, int file) { unsigned long nr_taken = 0; unsigned long nr_lumpy_taken = 0; unsigned long nr_lumpy_dirty = 0; unsigned long nr_lumpy_failed = 0; unsigned long scan; for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) { struct page *page; unsigned long pfn; unsigned long end_pfn; unsigned long page_pfn; int zone_id; page = lru_to_page(src); prefetchw_prev_lru_page(page, src, flags); VM_BUG_ON(!PageLRU(page)); switch (__isolate_lru_page(page, mode, file)) { case 0: list_move(&page->lru, dst); mem_cgroup_del_lru(page); nr_taken += hpage_nr_pages(page); break; case -EBUSY: /* else it is being freed elsewhere */ list_move(&page->lru, src); mem_cgroup_rotate_lru_list(page, page_lru(page)); continue; default: BUG(); } if (!order) continue; /* * Attempt to take all pages in the order aligned region * surrounding the tag page. Only take those pages of * the same active state as that tag page. We may safely * round the target page pfn down to the requested order * as the mem_map is guaranteed valid out to MAX_ORDER, * where that page is in a different zone we will detect * it from its zone id and abort this block scan. */ zone_id = page_zone_id(page); page_pfn = page_to_pfn(page); pfn = page_pfn & ~((1 << order) - 1); end_pfn = pfn + (1 << order); for (; pfn < end_pfn; pfn++) { struct page *cursor_page; /* The target page is in the block, ignore it. */ if (unlikely(pfn == page_pfn)) continue; /* Avoid holes within the zone. */ if (unlikely(!pfn_valid_within(pfn))) break; cursor_page = pfn_to_page(pfn); /* Check that we have not crossed a zone boundary. */ if (unlikely(page_zone_id(cursor_page) != zone_id)) break; /* * If we don't have enough swap space, reclaiming of * anon page which don't already have a swap slot is * pointless. */ if (nr_swap_pages <= 0 && PageSwapBacked(cursor_page) && !PageSwapCache(cursor_page)) break; if (__isolate_lru_page(cursor_page, mode, file) == 0) { list_move(&cursor_page->lru, dst); mem_cgroup_del_lru(cursor_page); nr_taken += hpage_nr_pages(page); nr_lumpy_taken++; if (PageDirty(cursor_page)) nr_lumpy_dirty++; scan++; } else { /* * Check if the page is freed already. * * We can't use page_count() as that * requires compound_head and we don't * have a pin on the page here. If a * page is tail, we may or may not * have isolated the head, so assume * it's not free, it'd be tricky to * track the head status without a * page pin. */ if (!PageTail(cursor_page) && !atomic_read(&cursor_page->_count)) continue; break; } } /* If we break out of the loop above, lumpy reclaim failed */ if (pfn < end_pfn) nr_lumpy_failed++; } *scanned = scan; trace_mm_vmscan_lru_isolate(order, nr_to_scan, scan, nr_taken, nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed, mode); return nr_taken; } static unsigned long isolate_pages_global(unsigned long nr, struct list_head *dst, unsigned long *scanned, int order, isolate_mode_t mode, struct zone *z, int active, int file) { int lru = LRU_BASE; if (active) lru += LRU_ACTIVE; if (file) lru += LRU_FILE; return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order, mode, file); } /* * clear_active_flags() is a helper for shrink_active_list(), clearing * any active bits from the pages in the list. */ static unsigned long clear_active_flags(struct list_head *page_list, unsigned int *count) { int nr_active = 0; int lru; struct page *page; list_for_each_entry(page, page_list, lru) { int numpages = hpage_nr_pages(page); lru = page_lru_base_type(page); if (PageActive(page)) { lru += LRU_ACTIVE; ClearPageActive(page); nr_active += numpages; } if (count) count[lru] += numpages; } return nr_active; } /** * isolate_lru_page - tries to isolate a page from its LRU list * @page: page to isolate from its LRU list * * Isolates a @page from an LRU list, clears PageLRU and adjusts the * vmstat statistic corresponding to whatever LRU list the page was on. * * Returns 0 if the page was removed from an LRU list. * Returns -EBUSY if the page was not on an LRU list. * * The returned page will have PageLRU() cleared. If it was found on * the active list, it will have PageActive set. If it was found on * the unevictable list, it will have the PageUnevictable bit set. That flag * may need to be cleared by the caller before letting the page go. * * The vmstat statistic corresponding to the list on which the page was * found will be decremented. * * Restrictions: * (1) Must be called with an elevated refcount on the page. This is a * fundamentnal difference from isolate_lru_pages (which is called * without a stable reference). * (2) the lru_lock must not be held. * (3) interrupts must be enabled. */ int isolate_lru_page(struct page *page) { int ret = -EBUSY; VM_BUG_ON(!page_count(page)); if (PageLRU(page)) { struct zone *zone = page_zone(page); spin_lock_irq(&zone->lru_lock); if (PageLRU(page)) { int lru = page_lru(page); ret = 0; get_page(page); ClearPageLRU(page); del_page_from_lru_list(zone, page, lru); } spin_unlock_irq(&zone->lru_lock); } return ret; } /* * Are there way too many processes in the direct reclaim path already? */ static int too_many_isolated(struct zone *zone, int file, struct scan_control *sc) { unsigned long inactive, isolated; if (current_is_kswapd()) return 0; if (!scanning_global_lru(sc)) return 0; if (file) { inactive = zone_page_state(zone, NR_INACTIVE_FILE); isolated = zone_page_state(zone, NR_ISOLATED_FILE); } else { inactive = zone_page_state(zone, NR_INACTIVE_ANON); isolated = zone_page_state(zone, NR_ISOLATED_ANON); } return isolated > inactive; } /* * TODO: Try merging with migrations version of putback_lru_pages */ static noinline_for_stack void putback_lru_pages(struct zone *zone, struct scan_control *sc, unsigned long nr_anon, unsigned long nr_file, struct list_head *page_list) { struct page *page; struct pagevec pvec; struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); pagevec_init(&pvec, 1); /* * Put back any unfreeable pages. */ spin_lock(&zone->lru_lock); while (!list_empty(page_list)) { int lru; page = lru_to_page(page_list); VM_BUG_ON(PageLRU(page)); list_del(&page->lru); if (unlikely(!page_evictable(page, NULL))) { spin_unlock_irq(&zone->lru_lock); putback_lru_page(page); spin_lock_irq(&zone->lru_lock); continue; } SetPageLRU(page); lru = page_lru(page); add_page_to_lru_list(zone, page, lru); if (is_active_lru(lru)) { int file = is_file_lru(lru); int numpages = hpage_nr_pages(page); reclaim_stat->recent_rotated[file] += numpages; } if (!pagevec_add(&pvec, page)) { spin_unlock_irq(&zone->lru_lock); __pagevec_release(&pvec); spin_lock_irq(&zone->lru_lock); } } __mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon); __mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file); spin_unlock_irq(&zone->lru_lock); pagevec_release(&pvec); } static noinline_for_stack void update_isolated_counts(struct zone *zone, struct scan_control *sc, unsigned long *nr_anon, unsigned long *nr_file, struct list_head *isolated_list) { unsigned long nr_active; unsigned int count[NR_LRU_LISTS] = { 0, }; struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); nr_active = clear_active_flags(isolated_list, count); __count_vm_events(PGDEACTIVATE, nr_active); __mod_zone_page_state(zone, NR_ACTIVE_FILE, -count[LRU_ACTIVE_FILE]); __mod_zone_page_state(zone, NR_INACTIVE_FILE, -count[LRU_INACTIVE_FILE]); __mod_zone_page_state(zone, NR_ACTIVE_ANON, -count[LRU_ACTIVE_ANON]); __mod_zone_page_state(zone, NR_INACTIVE_ANON, -count[LRU_INACTIVE_ANON]); *nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON]; *nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE]; __mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon); __mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file); reclaim_stat->recent_scanned[0] += *nr_anon; reclaim_stat->recent_scanned[1] += *nr_file; } /* * Returns true if the caller should wait to clean dirty/writeback pages. * * If we are direct reclaiming for contiguous pages and we do not reclaim * everything in the list, try again and wait for writeback IO to complete. * This will stall high-order allocations noticeably. Only do that when really * need to free the pages under high memory pressure. */ static inline bool should_reclaim_stall(unsigned long nr_taken, unsigned long nr_freed, int priority, struct scan_control *sc) { int lumpy_stall_priority; /* kswapd should not stall on sync IO */ if (current_is_kswapd()) return false; /* Only stall on lumpy reclaim */ if (sc->reclaim_mode & RECLAIM_MODE_SINGLE) return false; /* If we have relaimed everything on the isolated list, no stall */ if (nr_freed == nr_taken) return false; /* * For high-order allocations, there are two stall thresholds. * High-cost allocations stall immediately where as lower * order allocations such as stacks require the scanning * priority to be much higher before stalling. */ if (sc->order > PAGE_ALLOC_COSTLY_ORDER) lumpy_stall_priority = DEF_PRIORITY; else lumpy_stall_priority = DEF_PRIORITY / 3; return priority <= lumpy_stall_priority; } /* * shrink_inactive_list() is a helper for shrink_zone(). It returns the number * of reclaimed pages */ static noinline_for_stack unsigned long shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone, struct scan_control *sc, int priority, int file) { LIST_HEAD(page_list); unsigned long nr_scanned; unsigned long nr_reclaimed = 0; unsigned long nr_taken; unsigned long nr_anon; unsigned long nr_file; isolate_mode_t reclaim_mode = ISOLATE_INACTIVE; while (unlikely(too_many_isolated(zone, file, sc))) { congestion_wait(BLK_RW_ASYNC, HZ/10); /* We are about to die and free our memory. Return now. */ if (fatal_signal_pending(current)) return SWAP_CLUSTER_MAX; } set_reclaim_mode(priority, sc, false); if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM) reclaim_mode |= ISOLATE_ACTIVE; lru_add_drain(); if (!sc->may_unmap) reclaim_mode |= ISOLATE_UNMAPPED; if (!sc->may_writepage) reclaim_mode |= ISOLATE_CLEAN; spin_lock_irq(&zone->lru_lock); if (scanning_global_lru(sc)) { nr_taken = isolate_pages_global(nr_to_scan, &page_list, &nr_scanned, sc->order, reclaim_mode, zone, 0, file); zone->pages_scanned += nr_scanned; if (current_is_kswapd()) __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned); else __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned); } else { nr_taken = mem_cgroup_isolate_pages(nr_to_scan, &page_list, &nr_scanned, sc->order, reclaim_mode, zone, sc->mem_cgroup, 0, file); /* * mem_cgroup_isolate_pages() keeps track of * scanned pages on its own. */ } if (nr_taken == 0) { spin_unlock_irq(&zone->lru_lock); return 0; } update_isolated_counts(zone, sc, &nr_anon, &nr_file, &page_list); spin_unlock_irq(&zone->lru_lock); nr_reclaimed = shrink_page_list(&page_list, zone, sc); /* Check if we should syncronously wait for writeback */ if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) { set_reclaim_mode(priority, sc, true); nr_reclaimed += shrink_page_list(&page_list, zone, sc); } local_irq_disable(); if (current_is_kswapd()) __count_vm_events(KSWAPD_STEAL, nr_reclaimed); __count_zone_vm_events(PGSTEAL, zone, nr_reclaimed); putback_lru_pages(zone, sc, nr_anon, nr_file, &page_list); trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id, zone_idx(zone), nr_scanned, nr_reclaimed, priority, trace_shrink_flags(file, sc->reclaim_mode)); return nr_reclaimed; } /* * This moves pages from the active list to the inactive list. * * We move them the other way if the page is referenced by one or more * processes, from rmap. * * If the pages are mostly unmapped, the processing is fast and it is * appropriate to hold zone->lru_lock across the whole operation. But if * the pages are mapped, the processing is slow (page_referenced()) so we * should drop zone->lru_lock around each page. It's impossible to balance * this, so instead we remove the pages from the LRU while processing them. * It is safe to rely on PG_active against the non-LRU pages in here because * nobody will play with that bit on a non-LRU page. * * The downside is that we have to touch page->_count against each page. * But we had to alter page->flags anyway. */ static void move_active_pages_to_lru(struct zone *zone, struct list_head *list, enum lru_list lru) { unsigned long pgmoved = 0; struct pagevec pvec; struct page *page; pagevec_init(&pvec, 1); while (!list_empty(list)) { page = lru_to_page(list); VM_BUG_ON(PageLRU(page)); SetPageLRU(page); list_move(&page->lru, &zone->lru[lru].list); mem_cgroup_add_lru_list(page, lru); pgmoved += hpage_nr_pages(page); if (!pagevec_add(&pvec, page) || list_empty(list)) { spin_unlock_irq(&zone->lru_lock); if (buffer_heads_over_limit) pagevec_strip(&pvec); __pagevec_release(&pvec); spin_lock_irq(&zone->lru_lock); } } __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved); if (!is_active_lru(lru)) __count_vm_events(PGDEACTIVATE, pgmoved); } static void shrink_active_list(unsigned long nr_pages, struct zone *zone, struct scan_control *sc, int priority, int file) { unsigned long nr_taken; unsigned long pgscanned; unsigned long vm_flags; LIST_HEAD(l_hold); /* The pages which were snipped off */ LIST_HEAD(l_active); LIST_HEAD(l_inactive); struct page *page; struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); unsigned long nr_rotated = 0; isolate_mode_t reclaim_mode = ISOLATE_ACTIVE; lru_add_drain(); if (!sc->may_unmap) reclaim_mode |= ISOLATE_UNMAPPED; if (!sc->may_writepage) reclaim_mode |= ISOLATE_CLEAN; spin_lock_irq(&zone->lru_lock); if (scanning_global_lru(sc)) { nr_taken = isolate_pages_global(nr_pages, &l_hold, &pgscanned, sc->order, reclaim_mode, zone, 1, file); zone->pages_scanned += pgscanned; } else { nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold, &pgscanned, sc->order, reclaim_mode, zone, sc->mem_cgroup, 1, file); /* * mem_cgroup_isolate_pages() keeps track of * scanned pages on its own. */ } reclaim_stat->recent_scanned[file] += nr_taken; __count_zone_vm_events(PGREFILL, zone, pgscanned); if (file) __mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken); else __mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken); __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken); spin_unlock_irq(&zone->lru_lock); while (!list_empty(&l_hold)) { cond_resched(); page = lru_to_page(&l_hold); list_del(&page->lru); if (unlikely(!page_evictable(page, NULL))) { putback_lru_page(page); continue; } if (page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) { nr_rotated += hpage_nr_pages(page); /* * Identify referenced, file-backed active pages and * give them one more trip around the active list. So * that executable code get better chances to stay in * memory under moderate memory pressure. Anon pages * are not likely to be evicted by use-once streaming * IO, plus JVM can create lots of anon VM_EXEC pages, * so we ignore them here. */ if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) { list_add(&page->lru, &l_active); continue; } } ClearPageActive(page); /* we are de-activating */ list_add(&page->lru, &l_inactive); } /* * Move pages back to the lru list. */ spin_lock_irq(&zone->lru_lock); /* * Count referenced pages from currently used mappings as rotated, * even though only some of them are actually re-activated. This * helps balance scan pressure between file and anonymous pages in * get_scan_ratio. */ reclaim_stat->recent_rotated[file] += nr_rotated; move_active_pages_to_lru(zone, &l_active, LRU_ACTIVE + file * LRU_FILE); move_active_pages_to_lru(zone, &l_inactive, LRU_BASE + file * LRU_FILE); __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken); spin_unlock_irq(&zone->lru_lock); } #ifdef CONFIG_SWAP static int inactive_anon_is_low_global(struct zone *zone) { unsigned long active, inactive; active = zone_page_state(zone, NR_ACTIVE_ANON); inactive = zone_page_state(zone, NR_INACTIVE_ANON); if (inactive * zone->inactive_ratio < active) return 1; return 0; } /** * inactive_anon_is_low - check if anonymous pages need to be deactivated * @zone: zone to check * @sc: scan control of this context * * Returns true if the zone does not have enough inactive anon pages, * meaning some active anon pages need to be deactivated. */ static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc) { int low; /* * If we don't have swap space, anonymous page deactivation * is pointless. */ if (!total_swap_pages) return 0; if (scanning_global_lru(sc)) low = inactive_anon_is_low_global(zone); else low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup); return low; } #else static inline int inactive_anon_is_low(struct zone *zone, struct scan_control *sc) { return 0; } #endif static int inactive_file_is_low_global(struct zone *zone) { unsigned long active, inactive; active = zone_page_state(zone, NR_ACTIVE_FILE); inactive = zone_page_state(zone, NR_INACTIVE_FILE); return (active > inactive); } /** * inactive_file_is_low - check if file pages need to be deactivated * @zone: zone to check * @sc: scan control of this context * * When the system is doing streaming IO, memory pressure here * ensures that active file pages get deactivated, until more * than half of the file pages are on the inactive list. * * Once we get to that situation, protect the system's working * set from being evicted by disabling active file page aging. * * This uses a different ratio than the anonymous pages, because * the page cache uses a use-once replacement algorithm. */ static int inactive_file_is_low(struct zone *zone, struct scan_control *sc) { int low; if (scanning_global_lru(sc)) low = inactive_file_is_low_global(zone); else low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup); return low; } static int inactive_list_is_low(struct zone *zone, struct scan_control *sc, int file) { if (file) return inactive_file_is_low(zone, sc); else return inactive_anon_is_low(zone, sc); } static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan, struct zone *zone, struct scan_control *sc, int priority) { int file = is_file_lru(lru); if (is_active_lru(lru)) { if (inactive_list_is_low(zone, sc, file)) shrink_active_list(nr_to_scan, zone, sc, priority, file); return 0; } return shrink_inactive_list(nr_to_scan, zone, sc, priority, file); } /* * Determine how aggressively the anon and file LRU lists should be * scanned. The relative value of each set of LRU lists is determined * by looking at the fraction of the pages scanned we did rotate back * onto the active list instead of evict. * * nr[0] = anon pages to scan; nr[1] = file pages to scan */ static void get_scan_count(struct zone *zone, struct scan_control *sc, unsigned long *nr, int priority) { unsigned long anon, file, free; unsigned long anon_prio, file_prio; unsigned long ap, fp; struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); u64 fraction[2], denominator; enum lru_list l; int noswap = 0; bool force_scan = false; unsigned long nr_force_scan[2]; /* kswapd does zone balancing and needs to scan this zone */ if (scanning_global_lru(sc) && current_is_kswapd()) force_scan = true; /* memcg may have small limit and need to avoid priority drop */ if (!scanning_global_lru(sc)) force_scan = true; /* If we have no swap space, do not bother scanning anon pages. */ if (!sc->may_swap || (nr_swap_pages <= 0)) { noswap = 1; fraction[0] = 0; fraction[1] = 1; denominator = 1; nr_force_scan[0] = 0; nr_force_scan[1] = SWAP_CLUSTER_MAX; goto out; } anon = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) + zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON); file = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) + zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE); if (scanning_global_lru(sc)) { free = zone_page_state(zone, NR_FREE_PAGES); /* If we have very few page cache pages, force-scan anon pages. */ if (unlikely(file + free <= high_wmark_pages(zone))) { fraction[0] = 1; fraction[1] = 0; denominator = 1; nr_force_scan[0] = SWAP_CLUSTER_MAX; nr_force_scan[1] = 0; goto out; } } /* * With swappiness at 100, anonymous and file have the same priority. * This scanning priority is essentially the inverse of IO cost. */ anon_prio = sc->swappiness; file_prio = 200 - sc->swappiness; /* * OK, so we have swap space and a fair amount of page cache * pages. We use the recently rotated / recently scanned * ratios to determine how valuable each cache is. * * Because workloads change over time (and to avoid overflow) * we keep these statistics as a floating average, which ends * up weighing recent references more than old ones. * * anon in [0], file in [1] */ spin_lock_irq(&zone->lru_lock); if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) { reclaim_stat->recent_scanned[0] /= 2; reclaim_stat->recent_rotated[0] /= 2; } if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) { reclaim_stat->recent_scanned[1] /= 2; reclaim_stat->recent_rotated[1] /= 2; } /* * The amount of pressure on anon vs file pages is inversely * proportional to the fraction of recently scanned pages on * each list that were recently referenced and in active use. */ ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1); ap /= reclaim_stat->recent_rotated[0] + 1; fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1); fp /= reclaim_stat->recent_rotated[1] + 1; spin_unlock_irq(&zone->lru_lock); fraction[0] = ap; fraction[1] = fp; denominator = ap + fp + 1; if (force_scan) { unsigned long scan = SWAP_CLUSTER_MAX; nr_force_scan[0] = div64_u64(scan * ap, denominator); nr_force_scan[1] = div64_u64(scan * fp, denominator); } out: for_each_evictable_lru(l) { int file = is_file_lru(l); unsigned long scan; scan = zone_nr_lru_pages(zone, sc, l); if (priority || noswap) { scan >>= priority; scan = div64_u64(scan * fraction[file], denominator); } /* * If zone is small or memcg is small, nr[l] can be 0. * This results no-scan on this priority and priority drop down. * For global direct reclaim, it can visit next zone and tend * not to have problems. For global kswapd, it's for zone * balancing and it need to scan a small amounts. When using * memcg, priority drop can cause big latency. So, it's better * to scan small amount. See may_noscan above. */ if (!scan && force_scan) scan = nr_force_scan[file]; nr[l] = scan; } } /* * Reclaim/compaction depends on a number of pages being freed. To avoid * disruption to the system, a small number of order-0 pages continue to be * rotated and reclaimed in the normal fashion. However, by the time we get * back to the allocator and call try_to_compact_zone(), we ensure that * there are enough free pages for it to be likely successful */ static inline bool should_continue_reclaim(struct zone *zone, unsigned long nr_reclaimed, unsigned long nr_scanned, struct scan_control *sc) { unsigned long pages_for_compaction; unsigned long inactive_lru_pages; /* If not in reclaim/compaction mode, stop */ if (!(sc->reclaim_mode & RECLAIM_MODE_COMPACTION)) return false; /* Consider stopping depending on scan and reclaim activity */ if (sc->gfp_mask & __GFP_REPEAT) { /* * For __GFP_REPEAT allocations, stop reclaiming if the * full LRU list has been scanned and we are still failing * to reclaim pages. This full LRU scan is potentially * expensive but a __GFP_REPEAT caller really wants to succeed */ if (!nr_reclaimed && !nr_scanned) return false; } else { /* * For non-__GFP_REPEAT allocations which can presumably * fail without consequence, stop if we failed to reclaim * any pages from the last SWAP_CLUSTER_MAX number of * pages that were scanned. This will return to the * caller faster at the risk reclaim/compaction and * the resulting allocation attempt fails */ if (!nr_reclaimed) return false; } /* * If we have not reclaimed enough pages for compaction and the * inactive lists are large enough, continue reclaiming */ pages_for_compaction = (2UL << sc->order); inactive_lru_pages = zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE); if (nr_swap_pages > 0) inactive_lru_pages += zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON); if (sc->nr_reclaimed < pages_for_compaction && inactive_lru_pages > pages_for_compaction) return true; /* If compaction would go ahead or the allocation would succeed, stop */ switch (compaction_suitable(zone, sc->order)) { case COMPACT_PARTIAL: case COMPACT_CONTINUE: return false; default: return true; } } /* * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. */ static void shrink_zone(int priority, struct zone *zone, struct scan_control *sc) { unsigned long nr[NR_LRU_LISTS]; unsigned long nr_to_scan; enum lru_list l; unsigned long nr_reclaimed, nr_scanned; unsigned long nr_to_reclaim = sc->nr_to_reclaim; restart: nr_reclaimed = 0; nr_scanned = sc->nr_scanned; get_scan_count(zone, sc, nr, priority); while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || nr[LRU_INACTIVE_FILE]) { for_each_evictable_lru(l) { if (nr[l]) { nr_to_scan = min_t(unsigned long, nr[l], SWAP_CLUSTER_MAX); nr[l] -= nr_to_scan; nr_reclaimed += shrink_list(l, nr_to_scan, zone, sc, priority); } } /* * On large memory systems, scan >> priority can become * really large. This is fine for the starting priority; * we want to put equal scanning pressure on each zone. * However, if the VM has a harder time of freeing pages, * with multiple processes reclaiming pages, the total * freeing target can get unreasonably large. */ if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY) break; } sc->nr_reclaimed += nr_reclaimed; /* * Even if we did not try to evict anon pages at all, we want to * rebalance the anon lru active/inactive ratio. */ if (inactive_anon_is_low(zone, sc)) shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0); /* reclaim/compaction might need reclaim to continue */ if (should_continue_reclaim(zone, nr_reclaimed, sc->nr_scanned - nr_scanned, sc)) goto restart; throttle_vm_writeout(sc->gfp_mask); } /* Returns true if compaction should go ahead for a high-order request */ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc) { unsigned long balance_gap, watermark; bool watermark_ok; /* Do not consider compaction for orders reclaim is meant to satisfy */ if (sc->order <= PAGE_ALLOC_COSTLY_ORDER) return false; /* * Compaction takes time to run and there are potentially other * callers using the pages just freed. Continue reclaiming until * there is a buffer of free pages available to give compaction * a reasonable chance of completing and allocating the page */ balance_gap = min(low_wmark_pages(zone), (zone->present_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) / KSWAPD_ZONE_BALANCE_GAP_RATIO); watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order); watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0); /* * If compaction is deferred, reclaim up to a point where * compaction will have a chance of success when re-enabled */ if (compaction_deferred(zone)) return watermark_ok; /* If compaction is not ready to start, keep reclaiming */ if (!compaction_suitable(zone, sc->order)) return false; return watermark_ok; } /* * This is the direct reclaim path, for page-allocating processes. We only * try to reclaim pages from zones which will satisfy the caller's allocation * request. * * We reclaim from a zone even if that zone is over high_wmark_pages(zone). * Because: * a) The caller may be trying to free *extra* pages to satisfy a higher-order * allocation or * b) The target zone may be at high_wmark_pages(zone) but the lower zones * must go *over* high_wmark_pages(zone) to satisfy the `incremental min' * zone defense algorithm. * * If a zone is deemed to be full of pinned pages then just give it a light * scan then give up on it. * * This function returns true if a zone is being reclaimed for a costly * high-order allocation and compaction is ready to begin. This indicates to * the caller that it should consider retrying the allocation instead of * further reclaim. */ static bool shrink_zones(int priority, struct zonelist *zonelist, struct scan_control *sc) { struct zoneref *z; struct zone *zone; unsigned long nr_soft_reclaimed; unsigned long nr_soft_scanned; bool aborted_reclaim = false; for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(sc->gfp_mask), sc->nodemask) { if (!populated_zone(zone)) continue; /* * Take care memory controller reclaiming has small influence * to global LRU. */ if (scanning_global_lru(sc)) { if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) continue; if (zone->all_unreclaimable && priority != DEF_PRIORITY) continue; /* Let kswapd poll it */ if (COMPACTION_BUILD) { /* * If we already have plenty of memory free for * compaction in this zone, don't free any more. * Even though compaction is invoked for any * non-zero order, only frequent costly order * reclamation is disruptive enough to become a * noticable problem, like transparent huge page * allocations. */ if (compaction_ready(zone, sc)) { aborted_reclaim = true; continue; } } /* * This steals pages from memory cgroups over softlimit * and returns the number of reclaimed pages and * scanned pages. This works for global memory pressure * and balancing, not for a memcg's limit. */ nr_soft_scanned = 0; nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone, sc->order, sc->gfp_mask, &nr_soft_scanned); sc->nr_reclaimed += nr_soft_reclaimed; sc->nr_scanned += nr_soft_scanned; /* need some check for avoid more shrink_zone() */ } shrink_zone(priority, zone, sc); } return aborted_reclaim; } static bool zone_reclaimable(struct zone *zone) { return zone->pages_scanned < zone_reclaimable_pages(zone) * 6; } /* All zones in zonelist are unreclaimable? */ static bool all_unreclaimable(struct zonelist *zonelist, struct scan_control *sc) { struct zoneref *z; struct zone *zone; for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(sc->gfp_mask), sc->nodemask) { if (!populated_zone(zone)) continue; if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) continue; if (!zone->all_unreclaimable) return false; } return true; } /* * This is the main entry point to direct page reclaim. * * If a full scan of the inactive list fails to free enough memory then we * are "out of memory" and something needs to be killed. * * If the caller is !__GFP_FS then the probability of a failure is reasonably * high - the zone may be full of dirty or under-writeback pages, which this * caller can't do much about. We kick the writeback threads and take explicit * naps in the hope that some of these pages can be written. But if the * allocating task holds filesystem locks which prevent writeout this might not * work, and the allocation attempt will fail. * * returns: 0, if no pages reclaimed * else, the number of pages reclaimed */ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, struct scan_control *sc, struct shrink_control *shrink) { int priority; unsigned long total_scanned = 0; struct reclaim_state *reclaim_state = current->reclaim_state; struct zoneref *z; struct zone *zone; unsigned long writeback_threshold; bool aborted_reclaim; get_mems_allowed(); delayacct_freepages_start(); if (scanning_global_lru(sc)) count_vm_event(ALLOCSTALL); for (priority = DEF_PRIORITY; priority >= 0; priority--) { sc->nr_scanned = 0; if (!priority) disable_swap_token(sc->mem_cgroup); aborted_reclaim = shrink_zones(priority, zonelist, sc); /* * Don't shrink slabs when reclaiming memory from * over limit cgroups */ if (scanning_global_lru(sc)) { unsigned long lru_pages = 0; for_each_zone_zonelist(zone, z, zonelist, gfp_zone(sc->gfp_mask)) { if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) continue; lru_pages += zone_reclaimable_pages(zone); } shrink_slab(shrink, sc->nr_scanned, lru_pages); if (reclaim_state) { sc->nr_reclaimed += reclaim_state->reclaimed_slab; reclaim_state->reclaimed_slab = 0; } } total_scanned += sc->nr_scanned; if (sc->nr_reclaimed >= sc->nr_to_reclaim) goto out; /* * Try to write back as many pages as we just scanned. This * tends to cause slow streaming writers to write data to the * disk smoothly, at the dirtying rate, which is nice. But * that's undesirable in laptop mode, where we *want* lumpy * writeout. So in laptop mode, write out the whole world. */ writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2; if (total_scanned > writeback_threshold) { wakeup_flusher_threads(laptop_mode ? 0 : total_scanned); sc->may_writepage = 1; } /* Take a nap, wait for some writeback to complete */ if (!sc->hibernation_mode && sc->nr_scanned && priority < DEF_PRIORITY - 2) { struct zone *preferred_zone; first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask), &cpuset_current_mems_allowed, &preferred_zone); wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10); } } out: delayacct_freepages_end(); put_mems_allowed(); if (sc->nr_reclaimed) return sc->nr_reclaimed; /* * As hibernation is going on, kswapd is freezed so that it can't mark * the zone into all_unreclaimable. Thus bypassing all_unreclaimable * check. */ if (oom_killer_disabled) return 0; /* Aborted reclaim to try compaction? don't OOM, then */ if (aborted_reclaim) return 1; /* top priority shrink_zones still had more to do? don't OOM, then */ if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc)) return 1; return 0; } unsigned long try_to_free_pages(struct zonelist *zonelist, int order, gfp_t gfp_mask, nodemask_t *nodemask) { unsigned long nr_reclaimed; struct scan_control sc = { .gfp_mask = gfp_mask, .may_writepage = !laptop_mode, .nr_to_reclaim = SWAP_CLUSTER_MAX, .may_unmap = 1, .may_swap = 1, .swappiness = vm_swappiness, .order = order, .mem_cgroup = NULL, .nodemask = nodemask, }; struct shrink_control shrink = { .gfp_mask = sc.gfp_mask, }; trace_mm_vmscan_direct_reclaim_begin(order, sc.may_writepage, gfp_mask); nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); trace_mm_vmscan_direct_reclaim_end(nr_reclaimed); return nr_reclaimed; } #ifdef CONFIG_CGROUP_MEM_RES_CTLR unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem, gfp_t gfp_mask, bool noswap, unsigned int swappiness, struct zone *zone, unsigned long *nr_scanned) { struct scan_control sc = { .nr_scanned = 0, .nr_to_reclaim = SWAP_CLUSTER_MAX, .may_writepage = !laptop_mode, .may_unmap = 1, .may_swap = !noswap, .swappiness = swappiness, .order = 0, .mem_cgroup = mem, }; sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK); trace_mm_vmscan_memcg_softlimit_reclaim_begin(0, sc.may_writepage, sc.gfp_mask); /* * NOTE: Although we can get the priority field, using it * here is not a good idea, since it limits the pages we can scan. * if we don't reclaim here, the shrink_zone from balance_pgdat * will pick up pages from other mem cgroup's as well. We hack * the priority and make it zero. */ shrink_zone(0, zone, &sc); trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed); *nr_scanned = sc.nr_scanned; return sc.nr_reclaimed; } unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont, gfp_t gfp_mask, bool noswap, unsigned int swappiness) { struct zonelist *zonelist; unsigned long nr_reclaimed; int nid; struct scan_control sc = { .may_writepage = !laptop_mode, .may_unmap = 1, .may_swap = !noswap, .nr_to_reclaim = SWAP_CLUSTER_MAX, .swappiness = swappiness, .order = 0, .mem_cgroup = mem_cont, .nodemask = NULL, /* we don't care the placement */ .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK), }; struct shrink_control shrink = { .gfp_mask = sc.gfp_mask, }; /* * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't * take care of from where we get pages. So the node where we start the * scan does not need to be the current node. */ nid = mem_cgroup_select_victim_node(mem_cont); zonelist = NODE_DATA(nid)->node_zonelists; trace_mm_vmscan_memcg_reclaim_begin(0, sc.may_writepage, sc.gfp_mask); nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed); return nr_reclaimed; } #endif /* * pgdat_balanced is used when checking if a node is balanced for high-order * allocations. Only zones that meet watermarks and are in a zone allowed * by the callers classzone_idx are added to balanced_pages. The total of * balanced pages must be at least 25% of the zones allowed by classzone_idx * for the node to be considered balanced. Forcing all zones to be balanced * for high orders can cause excessive reclaim when there are imbalanced zones. * The choice of 25% is due to * o a 16M DMA zone that is balanced will not balance a zone on any * reasonable sized machine * o On all other machines, the top zone must be at least a reasonable * percentage of the middle zones. For example, on 32-bit x86, highmem * would need to be at least 256M for it to be balance a whole node. * Similarly, on x86-64 the Normal zone would need to be at least 1G * to balance a node on its own. These seemed like reasonable ratios. */ static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages, int classzone_idx) { unsigned long present_pages = 0; int i; for (i = 0; i <= classzone_idx; i++) present_pages += pgdat->node_zones[i].present_pages; /* A special case here: if zone has no page, we think it's balanced */ return balanced_pages >= (present_pages >> 2); } /* is kswapd sleeping prematurely? */ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining, int classzone_idx) { int i; unsigned long balanced = 0; bool all_zones_ok = true; /* If a direct reclaimer woke kswapd within HZ/10, it's premature */ if (remaining) return true; /* Check the watermark levels */ for (i = 0; i <= classzone_idx; i++) { struct zone *zone = pgdat->node_zones + i; if (!populated_zone(zone)) continue; /* * balance_pgdat() skips over all_unreclaimable after * DEF_PRIORITY. Effectively, it considers them balanced so * they must be considered balanced here as well if kswapd * is to sleep */ if (zone->all_unreclaimable) { balanced += zone->present_pages; continue; } if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone), i, 0)) all_zones_ok = false; else balanced += zone->present_pages; } /* * For high-order requests, the balanced zones must contain at least * 25% of the nodes pages for kswapd to sleep. For order-0, all zones * must be balanced */ if (order) return !pgdat_balanced(pgdat, balanced, classzone_idx); else return !all_zones_ok; } /* * For kswapd, balance_pgdat() will work across all this node's zones until * they are all at high_wmark_pages(zone). * * Returns the final order kswapd was reclaiming at * * There is special handling here for zones which are full of pinned pages. * This can happen if the pages are all mlocked, or if they are all used by * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb. * What we do is to detect the case where all pages in the zone have been * scanned twice and there has been zero successful reclaim. Mark the zone as * dead and from now on, only perform a short scan. Basically we're polling * the zone for when the problem goes away. * * kswapd scans the zones in the highmem->normal->dma direction. It skips * zones which have free_pages > high_wmark_pages(zone), but once a zone is * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the * lower zones regardless of the number of free pages in the lower zones. This * interoperates with the page allocator fallback scheme to ensure that aging * of pages is balanced across the zones. */ static unsigned long balance_pgdat(pg_data_t *pgdat, int order, int *classzone_idx) { int all_zones_ok; unsigned long balanced; int priority; int i; int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ unsigned long total_scanned; struct reclaim_state *reclaim_state = current->reclaim_state; unsigned long nr_soft_reclaimed; unsigned long nr_soft_scanned; struct scan_control sc = { .gfp_mask = GFP_KERNEL, .may_unmap = 1, .may_swap = 1, /* * kswapd doesn't want to be bailed out while reclaim. because * we want to put equal scanning pressure on each zone. */ .nr_to_reclaim = ULONG_MAX, .swappiness = vm_swappiness, .order = order, .mem_cgroup = NULL, }; struct shrink_control shrink = { .gfp_mask = sc.gfp_mask, }; loop_again: total_scanned = 0; sc.nr_reclaimed = 0; sc.may_writepage = !laptop_mode; count_vm_event(PAGEOUTRUN); for (priority = DEF_PRIORITY; priority >= 0; priority--) { unsigned long lru_pages = 0; int has_under_min_watermark_zone = 0; /* The swap token gets in the way of swapout... */ if (!priority) disable_swap_token(NULL); all_zones_ok = 1; balanced = 0; /* * Scan in the highmem->dma direction for the highest * zone which needs scanning */ for (i = pgdat->nr_zones - 1; i >= 0; i--) { struct zone *zone = pgdat->node_zones + i; if (!populated_zone(zone)) continue; if (zone->all_unreclaimable && priority != DEF_PRIORITY) continue; /* * Do some background aging of the anon list, to give * pages a chance to be referenced before reclaiming. */ if (inactive_anon_is_low(zone, &sc)) shrink_active_list(SWAP_CLUSTER_MAX, zone, &sc, priority, 0); if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone), 0, 0)) { end_zone = i; break; } else { /* If balanced, clear the congested flag */ zone_clear_flag(zone, ZONE_CONGESTED); } } if (i < 0) goto out; for (i = 0; i <= end_zone; i++) { struct zone *zone = pgdat->node_zones + i; lru_pages += zone_reclaimable_pages(zone); } /* * Now scan the zone in the dma->highmem direction, stopping * at the last zone which needs scanning. * * We do this because the page allocator works in the opposite * direction. This prevents the page allocator from allocating * pages behind kswapd's direction of progress, which would * cause too much scanning of the lower zones. */ for (i = 0; i <= end_zone; i++) { struct zone *zone = pgdat->node_zones + i; int nr_slab; unsigned long balance_gap; if (!populated_zone(zone)) continue; if (zone->all_unreclaimable && priority != DEF_PRIORITY) continue; sc.nr_scanned = 0; nr_soft_scanned = 0; /* * Call soft limit reclaim before calling shrink_zone. */ nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone, order, sc.gfp_mask, &nr_soft_scanned); sc.nr_reclaimed += nr_soft_reclaimed; total_scanned += nr_soft_scanned; /* * We put equal pressure on every zone, unless * one zone has way too many pages free * already. The "too many pages" is defined * as the high wmark plus a "gap" where the * gap is either the low watermark or 1% * of the zone, whichever is smaller. */ balance_gap = min(low_wmark_pages(zone), (zone->present_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) / KSWAPD_ZONE_BALANCE_GAP_RATIO); if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) + balance_gap, end_zone, 0)) { shrink_zone(priority, zone, &sc); reclaim_state->reclaimed_slab = 0; nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages); sc.nr_reclaimed += reclaim_state->reclaimed_slab; total_scanned += sc.nr_scanned; if (nr_slab == 0 && !zone_reclaimable(zone)) zone->all_unreclaimable = 1; } /* * If we've done a decent amount of scanning and * the reclaim ratio is low, start doing writepage * even in laptop mode */ if (total_scanned > SWAP_CLUSTER_MAX * 2 && total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2) sc.may_writepage = 1; if (zone->all_unreclaimable) { if (end_zone && end_zone == i) end_zone--; continue; } if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone), end_zone, 0)) { all_zones_ok = 0; /* * We are still under min water mark. This * means that we have a GFP_ATOMIC allocation * failure risk. Hurry up! */ if (!zone_watermark_ok_safe(zone, order, min_wmark_pages(zone), end_zone, 0)) has_under_min_watermark_zone = 1; } else { /* * If a zone reaches its high watermark, * consider it to be no longer congested. It's * possible there are dirty pages backed by * congested BDIs but as pressure is relieved, * spectulatively avoid congestion waits */ zone_clear_flag(zone, ZONE_CONGESTED); if (i <= *classzone_idx) balanced += zone->present_pages; } } if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx))) break; /* kswapd: all done */ /* * OK, kswapd is getting into trouble. Take a nap, then take * another pass across the zones. */ if (total_scanned && (priority < DEF_PRIORITY - 2)) { if (has_under_min_watermark_zone) count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT); else congestion_wait(BLK_RW_ASYNC, HZ/10); } /* * We do this so kswapd doesn't build up large priorities for * example when it is freeing in parallel with allocators. It * matches the direct reclaim path behaviour in terms of impact * on zone->*_priority. */ if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX) break; } out: /* * order-0: All zones must meet high watermark for a balanced node * high-order: Balanced zones must make up at least 25% of the node * for the node to be balanced */ if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) { cond_resched(); try_to_freeze(); /* * Fragmentation may mean that the system cannot be * rebalanced for high-order allocations in all zones. * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX, * it means the zones have been fully scanned and are still * not balanced. For high-order allocations, there is * little point trying all over again as kswapd may * infinite loop. * * Instead, recheck all watermarks at order-0 as they * are the most important. If watermarks are ok, kswapd will go * back to sleep. High-order users can still perform direct * reclaim if they wish. */ if (sc.nr_reclaimed < SWAP_CLUSTER_MAX) order = sc.order = 0; goto loop_again; } /* * If kswapd was reclaiming at a higher order, it has the option of * sleeping without all zones being balanced. Before it does, it must * ensure that the watermarks for order-0 on *all* zones are met and * that the congestion flags are cleared. The congestion flag must * be cleared as kswapd is the only mechanism that clears the flag * and it is potentially going to sleep here. */ if (order) { for (i = 0; i <= end_zone; i++) { struct zone *zone = pgdat->node_zones + i; if (!populated_zone(zone)) continue; if (zone->all_unreclaimable && priority != DEF_PRIORITY) continue; /* Confirm the zone is balanced for order-0 */ if (!zone_watermark_ok(zone, 0, high_wmark_pages(zone), 0, 0)) { order = sc.order = 0; goto loop_again; } /* If balanced, clear the congested flag */ zone_clear_flag(zone, ZONE_CONGESTED); } } /* * Return the order we were reclaiming at so sleeping_prematurely() * makes a decision on the order we were last reclaiming at. However, * if another caller entered the allocator slow path while kswapd * was awake, order will remain at the higher level */ *classzone_idx = end_zone; return order; } static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx) { long remaining = 0; DEFINE_WAIT(wait); if (freezing(current) || kthread_should_stop()) return; prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); /* Try to sleep for a short interval */ if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) { remaining = schedule_timeout(HZ/10); finish_wait(&pgdat->kswapd_wait, &wait); prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); } /* * After a short sleep, check if it was a premature sleep. If not, then * go fully to sleep until explicitly woken up. */ if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) { trace_mm_vmscan_kswapd_sleep(pgdat->node_id); /* * vmstat counters are not perfectly accurate and the estimated * value for counters such as NR_FREE_PAGES can deviate from the * true value by nr_online_cpus * threshold. To avoid the zone * watermarks being breached while under pressure, we reduce the * per-cpu vmstat threshold while kswapd is awake and restore * them before going back to sleep. */ set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold); if (!kthread_should_stop()) schedule(); set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold); } else { if (remaining) count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY); else count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY); } finish_wait(&pgdat->kswapd_wait, &wait); } /* * The background pageout daemon, started as a kernel thread * from the init process. * * This basically trickles out pages so that we have _some_ * free memory available even if there is no other activity * that frees anything up. This is needed for things like routing * etc, where we otherwise might have all activity going on in * asynchronous contexts that cannot page things out. * * If there are applications that are active memory-allocators * (most normal use), this basically shouldn't matter. */ static int kswapd(void *p) { unsigned long order, new_order; unsigned balanced_order; int classzone_idx, new_classzone_idx; int balanced_classzone_idx; pg_data_t *pgdat = (pg_data_t*)p; struct task_struct *tsk = current; struct reclaim_state reclaim_state = { .reclaimed_slab = 0, }; const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id); lockdep_set_current_reclaim_state(GFP_KERNEL); if (!cpumask_empty(cpumask)) set_cpus_allowed_ptr(tsk, cpumask); current->reclaim_state = &reclaim_state; /* * Tell the memory management that we're a "memory allocator", * and that if we need more memory we should get access to it * regardless (see "__alloc_pages()"). "kswapd" should * never get caught in the normal page freeing logic. * * (Kswapd normally doesn't need memory anyway, but sometimes * you need a small amount of memory in order to be able to * page out something else, and this flag essentially protects * us from recursively trying to free more memory as we're * trying to free the first piece of memory in the first place). */ tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; set_freezable(); order = new_order = 0; balanced_order = 0; classzone_idx = new_classzone_idx = pgdat->nr_zones - 1; balanced_classzone_idx = classzone_idx; for ( ; ; ) { int ret; /* * If the last balance_pgdat was unsuccessful it's unlikely a * new request of a similar or harder type will succeed soon * so consider going to sleep on the basis we reclaimed at */ if (balanced_classzone_idx >= new_classzone_idx && balanced_order == new_order) { new_order = pgdat->kswapd_max_order; new_classzone_idx = pgdat->classzone_idx; pgdat->kswapd_max_order = 0; pgdat->classzone_idx = pgdat->nr_zones - 1; } if (order < new_order || classzone_idx > new_classzone_idx) { /* * Don't sleep if someone wants a larger 'order' * allocation or has tigher zone constraints */ order = new_order; classzone_idx = new_classzone_idx; } else { kswapd_try_to_sleep(pgdat, balanced_order, balanced_classzone_idx); order = pgdat->kswapd_max_order; classzone_idx = pgdat->classzone_idx; new_order = order; new_classzone_idx = classzone_idx; pgdat->kswapd_max_order = 0; pgdat->classzone_idx = pgdat->nr_zones - 1; } ret = try_to_freeze(); if (kthread_should_stop()) break; /* * We can speed up thawing tasks if we don't call balance_pgdat * after returning from the refrigerator */ if (!ret) { trace_mm_vmscan_kswapd_wake(pgdat->node_id, order); balanced_classzone_idx = classzone_idx; balanced_order = balance_pgdat(pgdat, order, &balanced_classzone_idx); } } return 0; } /* * A zone is low on free memory, so wake its kswapd task to service it. */ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx) { pg_data_t *pgdat; if (!populated_zone(zone)) return; if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) return; pgdat = zone->zone_pgdat; if (pgdat->kswapd_max_order < order) { pgdat->kswapd_max_order = order; pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx); } if (!waitqueue_active(&pgdat->kswapd_wait)) return; if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0)) return; trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order); wake_up_interruptible(&pgdat->kswapd_wait); } /* * The reclaimable count would be mostly accurate. * The less reclaimable pages may be * - mlocked pages, which will be moved to unevictable list when encountered * - mapped pages, which may require several travels to be reclaimed * - dirty pages, which is not "instantly" reclaimable */ unsigned long global_reclaimable_pages(void) { int nr; nr = global_page_state(NR_ACTIVE_FILE) + global_page_state(NR_INACTIVE_FILE); if (nr_swap_pages > 0) nr += global_page_state(NR_ACTIVE_ANON) + global_page_state(NR_INACTIVE_ANON); return nr; } unsigned long zone_reclaimable_pages(struct zone *zone) { int nr; nr = zone_page_state(zone, NR_ACTIVE_FILE) + zone_page_state(zone, NR_INACTIVE_FILE); if (nr_swap_pages > 0) nr += zone_page_state(zone, NR_ACTIVE_ANON) + zone_page_state(zone, NR_INACTIVE_ANON); return nr; } #ifdef CONFIG_HIBERNATION /* * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of * freed pages. * * Rather than trying to age LRUs the aim is to preserve the overall * LRU order by reclaiming preferentially * inactive > active > active referenced > active mapped */ unsigned long shrink_all_memory(unsigned long nr_to_reclaim) { struct reclaim_state reclaim_state; struct scan_control sc = { .gfp_mask = GFP_HIGHUSER_MOVABLE, .may_swap = 1, .may_unmap = 1, .may_writepage = 1, .nr_to_reclaim = nr_to_reclaim, .hibernation_mode = 1, .swappiness = vm_swappiness, .order = 0, }; struct shrink_control shrink = { .gfp_mask = sc.gfp_mask, }; struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask); struct task_struct *p = current; unsigned long nr_reclaimed; p->flags |= PF_MEMALLOC; lockdep_set_current_reclaim_state(sc.gfp_mask); reclaim_state.reclaimed_slab = 0; p->reclaim_state = &reclaim_state; nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); p->reclaim_state = NULL; lockdep_clear_current_reclaim_state(); p->flags &= ~PF_MEMALLOC; return nr_reclaimed; } #endif /* CONFIG_HIBERNATION */ /* It's optimal to keep kswapds 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 __devinit cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu) { int nid; if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) { for_each_node_state(nid, N_HIGH_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 */ set_cpus_allowed_ptr(pgdat->kswapd, mask); } } return NOTIFY_OK; } /* * This kswapd start function will be called by init and node-hot-add. * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added. */ int kswapd_run(int nid) { pg_data_t *pgdat = NODE_DATA(nid); int ret = 0; if (pgdat->kswapd) return 0; pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid); if (IS_ERR(pgdat->kswapd)) { /* failure at boot is fatal */ BUG_ON(system_state == SYSTEM_BOOTING); printk("Failed to start kswapd on node %d\n",nid); ret = -1; } return ret; } /* * Called by memory hotplug when all memory in a node is offlined. Caller must * hold lock_memory_hotplug(). */ void kswapd_stop(int nid) { struct task_struct *kswapd = NODE_DATA(nid)->kswapd; if (kswapd) { kthread_stop(kswapd); NODE_DATA(nid)->kswapd = NULL; } } static int __init kswapd_init(void) { int nid; swap_setup(); for_each_node_state(nid, N_HIGH_MEMORY) kswapd_run(nid); hotcpu_notifier(cpu_callback, 0); return 0; } module_init(kswapd_init) #ifdef CONFIG_NUMA /* * Zone reclaim mode * * If non-zero call zone_reclaim when the number of free pages falls below * the watermarks. */ int zone_reclaim_mode __read_mostly; #define RECLAIM_OFF 0 #define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */ /* * Priority for ZONE_RECLAIM. This determines the fraction of pages * of a node considered for each zone_reclaim. 4 scans 1/16th of * a zone. */ #define ZONE_RECLAIM_PRIORITY 4 /* * Percentage of pages in a zone that must be unmapped for zone_reclaim to * occur. */ int sysctl_min_unmapped_ratio = 1; /* * If the number of slab pages in a zone grows beyond this percentage then * slab reclaim needs to occur. */ int sysctl_min_slab_ratio = 5; static inline unsigned long zone_unmapped_file_pages(struct zone *zone) { unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED); unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) + zone_page_state(zone, NR_ACTIVE_FILE); /* * It's possible for there to be more file mapped pages than * accounted for by the pages on the file LRU lists because * tmpfs pages accounted for as ANON can also be FILE_MAPPED */ return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0; } /* Work out how many page cache pages we can reclaim in this reclaim_mode */ static long zone_pagecache_reclaimable(struct zone *zone) { long nr_pagecache_reclaimable; long delta = 0; /* * If RECLAIM_SWAP is set, then all file pages are considered * potentially reclaimable. Otherwise, we have to worry about * pages like swapcache and zone_unmapped_file_pages() provides * a better estimate */ if (zone_reclaim_mode & RECLAIM_SWAP) nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES); else nr_pagecache_reclaimable = zone_unmapped_file_pages(zone); /* If we can't clean pages, remove dirty pages from consideration */ if (!(zone_reclaim_mode & RECLAIM_WRITE)) delta += zone_page_state(zone, NR_FILE_DIRTY); /* Watch for any possible underflows due to delta */ if (unlikely(delta > nr_pagecache_reclaimable)) delta = nr_pagecache_reclaimable; return nr_pagecache_reclaimable - delta; } /* * Try to free up some pages from this zone through reclaim. */ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) { /* Minimum pages needed in order to stay on node */ const unsigned long nr_pages = 1 << order; struct task_struct *p = current; struct reclaim_state reclaim_state; int priority; struct scan_control sc = { .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE), .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP), .may_swap = 1, .nr_to_reclaim = max_t(unsigned long, nr_pages, SWAP_CLUSTER_MAX), .gfp_mask = gfp_mask, .swappiness = vm_swappiness, .order = order, }; struct shrink_control shrink = { .gfp_mask = sc.gfp_mask, }; unsigned long nr_slab_pages0, nr_slab_pages1; cond_resched(); /* * We need to be able to allocate from the reserves for RECLAIM_SWAP * and we also need to be able to write out pages for RECLAIM_WRITE * and RECLAIM_SWAP. */ p->flags |= PF_MEMALLOC | PF_SWAPWRITE; lockdep_set_current_reclaim_state(gfp_mask); reclaim_state.reclaimed_slab = 0; p->reclaim_state = &reclaim_state; if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) { /* * Free memory by calling shrink zone with increasing * priorities until we have enough memory freed. */ priority = ZONE_RECLAIM_PRIORITY; do { shrink_zone(priority, zone, &sc); priority--; } while (priority >= 0 && sc.nr_reclaimed < nr_pages); } nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE); if (nr_slab_pages0 > zone->min_slab_pages) { /* * shrink_slab() does not currently allow us to determine how * many pages were freed in this zone. So we take the current * number of slab pages and shake the slab until it is reduced * by the same nr_pages that we used for reclaiming unmapped * pages. * * Note that shrink_slab will free memory on all zones and may * take a long time. */ for (;;) { unsigned long lru_pages = zone_reclaimable_pages(zone); /* No reclaimable slab or very low memory pressure */ if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages)) break; /* Freed enough memory */ nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE); if (nr_slab_pages1 + nr_pages <= nr_slab_pages0) break; } /* * Update nr_reclaimed by the number of slab pages we * reclaimed from this zone. */ nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE); if (nr_slab_pages1 < nr_slab_pages0) sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1; } p->reclaim_state = NULL; current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE); lockdep_clear_current_reclaim_state(); return sc.nr_reclaimed >= nr_pages; } int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) { int node_id; int ret; /* * Zone reclaim reclaims unmapped file backed pages and * slab pages if we are over the defined limits. * * A small portion of unmapped file backed pages is needed for * file I/O otherwise pages read by file I/O will be immediately * thrown out if the zone is overallocated. So we do not reclaim * if less than a specified percentage of the zone is used by * unmapped file backed pages. */ if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages && zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages) return ZONE_RECLAIM_FULL; if (zone->all_unreclaimable) return ZONE_RECLAIM_FULL; /* * Do not scan if the allocation should not be delayed. */ if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC)) return ZONE_RECLAIM_NOSCAN; /* * Only run zone reclaim on the local zone or on zones that do not * have associated processors. This will favor the local processor * over remote processors and spread off node memory allocations * as wide as possible. */ node_id = zone_to_nid(zone); if (node_state(node_id, N_CPU) && node_id != numa_node_id()) return ZONE_RECLAIM_NOSCAN; if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED)) return ZONE_RECLAIM_NOSCAN; ret = __zone_reclaim(zone, gfp_mask, order); zone_clear_flag(zone, ZONE_RECLAIM_LOCKED); if (!ret) count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED); return ret; } #endif /* * page_evictable - test whether a page is evictable * @page: the page to test * @vma: the VMA in which the page is or will be mapped, may be NULL * * Test whether page is evictable--i.e., should be placed on active/inactive * lists vs unevictable list. The vma argument is !NULL when called from the * fault path to determine how to instantate a new page. * * Reasons page might not be evictable: * (1) page's mapping marked unevictable * (2) page is part of an mlocked VMA * */ int page_evictable(struct page *page, struct vm_area_struct *vma) { if (mapping_unevictable(page_mapping(page))) return 0; if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page))) return 0; return 1; } /** * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list * @page: page to check evictability and move to appropriate lru list * @zone: zone page is in * * Checks a page for evictability and moves the page to the appropriate * zone lru list. * * Restrictions: zone->lru_lock must be held, page must be on LRU and must * have PageUnevictable set. */ static void check_move_unevictable_page(struct page *page, struct zone *zone) { VM_BUG_ON(PageActive(page)); retry: ClearPageUnevictable(page); if (page_evictable(page, NULL)) { enum lru_list l = page_lru_base_type(page); __dec_zone_state(zone, NR_UNEVICTABLE); list_move(&page->lru, &zone->lru[l].list); mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l); __inc_zone_state(zone, NR_INACTIVE_ANON + l); __count_vm_event(UNEVICTABLE_PGRESCUED); } else { /* * rotate unevictable list */ SetPageUnevictable(page); list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list); mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE); if (page_evictable(page, NULL)) goto retry; } } /** * scan_mapping_unevictable_pages - scan an address space for evictable pages * @mapping: struct address_space to scan for evictable pages * * Scan all pages in mapping. Check unevictable pages for * evictability and move them to the appropriate zone lru list. */ void scan_mapping_unevictable_pages(struct address_space *mapping) { pgoff_t next = 0; pgoff_t end = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT; struct zone *zone; struct pagevec pvec; if (mapping->nrpages == 0) return; pagevec_init(&pvec, 0); while (next < end && pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) { int i; int pg_scanned = 0; zone = NULL; for (i = 0; i < pagevec_count(&pvec); i++) { struct page *page = pvec.pages[i]; pgoff_t page_index = page->index; struct zone *pagezone = page_zone(page); pg_scanned++; if (page_index > next) next = page_index; next++; if (pagezone != zone) { if (zone) spin_unlock_irq(&zone->lru_lock); zone = pagezone; spin_lock_irq(&zone->lru_lock); } if (PageLRU(page) && PageUnevictable(page)) check_move_unevictable_page(page, zone); } if (zone) spin_unlock_irq(&zone->lru_lock); pagevec_release(&pvec); count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned); } } /** * scan_zone_unevictable_pages - check unevictable list for evictable pages * @zone - zone of which to scan the unevictable list * * Scan @zone's unevictable LRU lists to check for pages that have become * evictable. Move those that have to @zone's inactive list where they * become candidates for reclaim, unless shrink_inactive_zone() decides * to reactivate them. Pages that are still unevictable are rotated * back onto @zone's unevictable list. */ #define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */ static void scan_zone_unevictable_pages(struct zone *zone) { struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list; unsigned long scan; unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE); while (nr_to_scan > 0) { unsigned long batch_size = min(nr_to_scan, SCAN_UNEVICTABLE_BATCH_SIZE); spin_lock_irq(&zone->lru_lock); for (scan = 0; scan < batch_size; scan++) { struct page *page = lru_to_page(l_unevictable); if (!trylock_page(page)) continue; prefetchw_prev_lru_page(page, l_unevictable, flags); if (likely(PageLRU(page) && PageUnevictable(page))) check_move_unevictable_page(page, zone); unlock_page(page); } spin_unlock_irq(&zone->lru_lock); nr_to_scan -= batch_size; } } /** * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages * * A really big hammer: scan all zones' unevictable LRU lists to check for * pages that have become evictable. Move those back to the zones' * inactive list where they become candidates for reclaim. * This occurs when, e.g., we have unswappable pages on the unevictable lists, * and we add swap to the system. As such, it runs in the context of a task * that has possibly/probably made some previously unevictable pages * evictable. */ static void scan_all_zones_unevictable_pages(void) { struct zone *zone; for_each_zone(zone) { scan_zone_unevictable_pages(zone); } } /* * scan_unevictable_pages [vm] sysctl handler. On demand re-scan of * all nodes' unevictable lists for evictable pages */ unsigned long scan_unevictable_pages; int scan_unevictable_handler(struct ctl_table *table, int write, void __user *buffer, size_t *length, loff_t *ppos) { proc_doulongvec_minmax(table, write, buffer, length, ppos); if (write && *(unsigned long *)table->data) scan_all_zones_unevictable_pages(); scan_unevictable_pages = 0; return 0; } #ifdef CONFIG_NUMA /* * per node 'scan_unevictable_pages' attribute. On demand re-scan of * a specified node's per zone unevictable lists for evictable pages. */ static ssize_t read_scan_unevictable_node(struct sys_device *dev, struct sysdev_attribute *attr, char *buf) { return sprintf(buf, "0\n"); /* always zero; should fit... */ } static ssize_t write_scan_unevictable_node(struct sys_device *dev, struct sysdev_attribute *attr, const char *buf, size_t count) { struct zone *node_zones = NODE_DATA(dev->id)->node_zones; struct zone *zone; unsigned long res; unsigned long req = strict_strtoul(buf, 10, &res); if (!req) return 1; /* zero is no-op */ for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) { if (!populated_zone(zone)) continue; scan_zone_unevictable_pages(zone); } return 1; } static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR, read_scan_unevictable_node, write_scan_unevictable_node); int scan_unevictable_register_node(struct node *node) { return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages); } void scan_unevictable_unregister_node(struct node *node) { sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages); } #endif