/* * 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 #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 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 order; /* Scan (total_size >> priority) pages at once */ int priority; /* * The memory cgroup that hit its limit and as a result is the * primary target of this reclaim invocation. */ struct mem_cgroup *target_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; unsigned 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_MEMCG static bool global_reclaim(struct scan_control *sc) { return !sc->target_mem_cgroup; } #else static bool global_reclaim(struct scan_control *sc) { return true; } #endif 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 (get_nr_swap_pages() > 0) nr += zone_page_state(zone, NR_ACTIVE_ANON) + zone_page_state(zone, NR_INACTIVE_ANON); return nr; } bool zone_reclaimable(struct zone *zone) { return zone->pages_scanned < zone_reclaimable_pages(zone) * 6; } static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru) { if (!mem_cgroup_disabled()) return mem_cgroup_get_lru_size(lruvec, lru); return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru); } /* * Add a shrinker callback to be called from the vm. */ int register_shrinker(struct shrinker *shrinker) { size_t size = sizeof(*shrinker->nr_deferred); /* * If we only have one possible node in the system anyway, save * ourselves the trouble and disable NUMA aware behavior. This way we * will save memory and some small loop time later. */ if (nr_node_ids == 1) shrinker->flags &= ~SHRINKER_NUMA_AWARE; if (shrinker->flags & SHRINKER_NUMA_AWARE) size *= nr_node_ids; shrinker->nr_deferred = kzalloc(size, GFP_KERNEL); if (!shrinker->nr_deferred) return -ENOMEM; down_write(&shrinker_rwsem); list_add_tail(&shrinker->list, &shrinker_list); up_write(&shrinker_rwsem); return 0; } 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); #define SHRINK_BATCH 128 static unsigned long shrink_slab_node(struct shrink_control *shrinkctl, struct shrinker *shrinker, unsigned long nr_pages_scanned, unsigned long lru_pages) { unsigned long freed = 0; unsigned long long delta; long total_scan; long max_pass; long nr; long new_nr; int nid = shrinkctl->nid; long batch_size = shrinker->batch ? shrinker->batch : SHRINK_BATCH; max_pass = shrinker->count_objects(shrinker, shrinkctl); if (max_pass == 0) return 0; /* * 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. */ nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0); total_scan = nr; 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->scan_objects, 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, shrinkctl, nr, nr_pages_scanned, lru_pages, max_pass, delta, total_scan); while (total_scan >= batch_size) { unsigned long ret; shrinkctl->nr_to_scan = batch_size; ret = shrinker->scan_objects(shrinker, shrinkctl); if (ret == SHRINK_STOP) break; freed += ret; count_vm_events(SLABS_SCANNED, batch_size); total_scan -= batch_size; 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. */ if (total_scan > 0) new_nr = atomic_long_add_return(total_scan, &shrinker->nr_deferred[nid]); else new_nr = atomic_long_read(&shrinker->nr_deferred[nid]); trace_mm_shrink_slab_end(shrinker, freed, nr, new_nr); return freed; } /* * 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 *shrinkctl, unsigned long nr_pages_scanned, unsigned long lru_pages) { struct shrinker *shrinker; unsigned long freed = 0; if (nr_pages_scanned == 0) nr_pages_scanned = SWAP_CLUSTER_MAX; if (!down_read_trylock(&shrinker_rwsem)) { /* * If we would return 0, our callers would understand that we * have nothing else to shrink and give up trying. By returning * 1 we keep it going and assume we'll be able to shrink next * time. */ freed = 1; goto out; } list_for_each_entry(shrinker, &shrinker_list, list) { for_each_node_mask(shrinkctl->nid, shrinkctl->nodes_to_scan) { if (!node_online(shrinkctl->nid)) continue; if (!(shrinker->flags & SHRINKER_NUMA_AWARE) && (shrinkctl->nid != 0)) break; freed += shrink_slab_node(shrinkctl, shrinker, nr_pages_scanned, lru_pages); } } up_read(&shrinker_rwsem); out: cond_resched(); return freed; } 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; 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; } if (!PageWriteback(page)) { /* synchronous write or broken a_ops? */ ClearPageReclaim(page); } trace_mm_vmscan_writepage(page, trace_reclaim_flags(page)); 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) { bool is_unevictable; int was_unevictable = PageUnevictable(page); VM_BUG_ON(PageLRU(page)); redo: ClearPageUnevictable(page); if (page_evictable(page)) { /* * 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. */ is_unevictable = false; lru_cache_add(page); } else { /* * Put unevictable pages directly on zone's unevictable * list. */ is_unevictable = true; add_page_to_unevictable_list(page); /* * When racing with an mlock or AS_UNEVICTABLE clearing * (page is unlocked) make sure that if the other thread * does not observe our setting of PG_lru and fails * isolation/check_move_unevictable_pages, * we see PG_mlocked/AS_UNEVICTABLE cleared below and move * the page back to the evictable list. * * The other side is TestClearPageMlocked() or shmem_lock(). */ 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 (is_unevictable && page_evictable(page)) { 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 && !is_unevictable) count_vm_event(UNEVICTABLE_PGRESCUED); else if (!was_unevictable && is_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->target_mem_cgroup, &vm_flags); referenced_page = TestClearPageReferenced(page); /* * 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; } /* Check if a page is dirty or under writeback */ static void page_check_dirty_writeback(struct page *page, bool *dirty, bool *writeback) { struct address_space *mapping; /* * Anonymous pages are not handled by flushers and must be written * from reclaim context. Do not stall reclaim based on them */ if (!page_is_file_cache(page)) { *dirty = false; *writeback = false; return; } /* By default assume that the page flags are accurate */ *dirty = PageDirty(page); *writeback = PageWriteback(page); /* Verify dirty/writeback state if the filesystem supports it */ if (!page_has_private(page)) return; mapping = page_mapping(page); if (mapping && mapping->a_ops->is_dirty_writeback) mapping->a_ops->is_dirty_writeback(page, dirty, writeback); } /* * 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, enum ttu_flags ttu_flags, unsigned long *ret_nr_dirty, unsigned long *ret_nr_unqueued_dirty, unsigned long *ret_nr_congested, unsigned long *ret_nr_writeback, unsigned long *ret_nr_immediate, bool force_reclaim) { LIST_HEAD(ret_pages); LIST_HEAD(free_pages); int pgactivate = 0; unsigned long nr_unqueued_dirty = 0; unsigned long nr_dirty = 0; unsigned long nr_congested = 0; unsigned long nr_reclaimed = 0; unsigned long nr_writeback = 0; unsigned long nr_immediate = 0; cond_resched(); mem_cgroup_uncharge_start(); while (!list_empty(page_list)) { struct address_space *mapping; struct page *page; int may_enter_fs; enum page_references references = PAGEREF_RECLAIM_CLEAN; bool dirty, writeback; 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))) 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)); /* * The number of dirty pages determines if a zone is marked * reclaim_congested which affects wait_iff_congested. kswapd * will stall and start writing pages if the tail of the LRU * is all dirty unqueued pages. */ page_check_dirty_writeback(page, &dirty, &writeback); if (dirty || writeback) nr_dirty++; if (dirty && !writeback) nr_unqueued_dirty++; /* * Treat this page as congested if the underlying BDI is or if * pages are cycling through the LRU so quickly that the * pages marked for immediate reclaim are making it to the * end of the LRU a second time. */ mapping = page_mapping(page); if ((mapping && bdi_write_congested(mapping->backing_dev_info)) || (writeback && PageReclaim(page))) nr_congested++; /* * If a page at the tail of the LRU is under writeback, there * are three cases to consider. * * 1) If reclaim is encountering an excessive number of pages * under writeback and this page is both under writeback and * PageReclaim then it indicates that pages are being queued * for IO but are being recycled through the LRU before the * IO can complete. Waiting on the page itself risks an * indefinite stall if it is impossible to writeback the * page due to IO error or disconnected storage so instead * note that the LRU is being scanned too quickly and the * caller can stall after page list has been processed. * * 2) Global reclaim encounters a page, memcg encounters a * page that is not marked for immediate reclaim or * the caller does not have __GFP_IO. In this case mark * the page for immediate reclaim and continue scanning. * * __GFP_IO is checked because a loop driver thread might * enter reclaim, and deadlock if it waits on a page for * which it is needed to do the write (loop masks off * __GFP_IO|__GFP_FS for this reason); but more thought * would probably show more reasons. * * Don't require __GFP_FS, since we're not going into the * FS, just waiting on its writeback completion. Worryingly, * ext4 gfs2 and xfs allocate pages with * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so testing * may_enter_fs here is liable to OOM on them. * * 3) memcg encounters a page that is not already marked * PageReclaim. memcg does not have any dirty pages * throttling so we could easily OOM just because too many * pages are in writeback and there is nothing else to * reclaim. Wait for the writeback to complete. */ if (PageWriteback(page)) { /* Case 1 above */ if (current_is_kswapd() && PageReclaim(page) && zone_is_reclaim_writeback(zone)) { nr_immediate++; goto keep_locked; /* Case 2 above */ } else if (global_reclaim(sc) || !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) { /* * This is slightly racy - end_page_writeback() * might have just cleared PageReclaim, then * setting PageReclaim here end up interpreted * as PageReadahead - but that does not matter * enough to care. What we do want is for this * page to have PageReclaim set next time memcg * reclaim reaches the tests above, so it will * then wait_on_page_writeback() to avoid OOM; * and it's also appropriate in global reclaim. */ SetPageReclaim(page); nr_writeback++; goto keep_locked; /* Case 3 above */ } else { wait_on_page_writeback(page); } } if (!force_reclaim) 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, page_list)) goto activate_locked; may_enter_fs = 1; /* Adding to swap updated mapping */ 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_flags)) { 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)) { /* * Only kswapd can writeback filesystem pages to * avoid risk of stack overflow but only writeback * if many dirty pages have been encountered. */ if (page_is_file_cache(page) && (!current_is_kswapd() || !zone_is_reclaim_dirty(zone))) { /* * Immediately reclaim when written back. * Similar in principal to deactivate_page() * except we already have the page isolated * and know it's dirty */ inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE); SetPageReclaim(page); goto keep_locked; } 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: goto keep_locked; case PAGE_ACTIVATE: goto activate_locked; case PAGE_SUCCESS: if (PageWriteback(page)) goto keep; 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); 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: list_add(&page->lru, &ret_pages); VM_BUG_ON(PageLRU(page) || PageUnevictable(page)); } free_hot_cold_page_list(&free_pages, 1); list_splice(&ret_pages, page_list); count_vm_events(PGACTIVATE, pgactivate); mem_cgroup_uncharge_end(); *ret_nr_dirty += nr_dirty; *ret_nr_congested += nr_congested; *ret_nr_unqueued_dirty += nr_unqueued_dirty; *ret_nr_writeback += nr_writeback; *ret_nr_immediate += nr_immediate; return nr_reclaimed; } unsigned long reclaim_clean_pages_from_list(struct zone *zone, struct list_head *page_list) { struct scan_control sc = { .gfp_mask = GFP_KERNEL, .priority = DEF_PRIORITY, .may_unmap = 1, }; unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5; struct page *page, *next; LIST_HEAD(clean_pages); list_for_each_entry_safe(page, next, page_list, lru) { if (page_is_file_cache(page) && !PageDirty(page) && !isolated_balloon_page(page)) { ClearPageActive(page); list_move(&page->lru, &clean_pages); } } ret = shrink_page_list(&clean_pages, zone, &sc, TTU_UNMAP|TTU_IGNORE_ACCESS, &dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true); list_splice(&clean_pages, page_list); __mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret); return ret; } /* * 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 ret = -EINVAL; /* Only take pages on the LRU. */ if (!PageLRU(page)) return ret; /* Compaction should not handle unevictable pages but CMA can do so */ if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE)) 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. * @lruvec: The LRU vector to pull pages from. * @dst: The temp list to put pages on to. * @nr_scanned: The number of pages that were scanned. * @sc: The scan_control struct for this reclaim session * @mode: One of the LRU isolation modes * @lru: LRU list id for isolating * * returns how many pages were moved onto *@dst. */ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, struct lruvec *lruvec, struct list_head *dst, unsigned long *nr_scanned, struct scan_control *sc, isolate_mode_t mode, enum lru_list lru) { struct list_head *src = &lruvec->lists[lru]; unsigned long nr_taken = 0; unsigned long scan; for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) { struct page *page; int nr_pages; page = lru_to_page(src); prefetchw_prev_lru_page(page, src, flags); VM_BUG_ON(!PageLRU(page)); switch (__isolate_lru_page(page, mode)) { case 0: nr_pages = hpage_nr_pages(page); mem_cgroup_update_lru_size(lruvec, lru, -nr_pages); list_move(&page->lru, dst); nr_taken += nr_pages; break; case -EBUSY: /* else it is being freed elsewhere */ list_move(&page->lru, src); continue; default: BUG(); } } *nr_scanned = scan; trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan, nr_taken, mode, is_file_lru(lru)); return nr_taken; } /** * 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); struct lruvec *lruvec; spin_lock_irq(&zone->lru_lock); lruvec = mem_cgroup_page_lruvec(page, zone); if (PageLRU(page)) { int lru = page_lru(page); get_page(page); ClearPageLRU(page); del_page_from_lru_list(page, lruvec, lru); ret = 0; } spin_unlock_irq(&zone->lru_lock); } return ret; } /* * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and * then get resheduled. When there are massive number of tasks doing page * allocation, such sleeping direct reclaimers may keep piling up on each CPU, * the LRU list will go small and be scanned faster than necessary, leading to * unnecessary swapping, thrashing and OOM. */ 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 (!global_reclaim(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); } /* * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they * won't get blocked by normal direct-reclaimers, forming a circular * deadlock. */ if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS) inactive >>= 3; return isolated > inactive; } static noinline_for_stack void putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list) { struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; struct zone *zone = lruvec_zone(lruvec); LIST_HEAD(pages_to_free); /* * Put back any unfreeable pages. */ while (!list_empty(page_list)) { struct page *page = lru_to_page(page_list); int lru; VM_BUG_ON(PageLRU(page)); list_del(&page->lru); if (unlikely(!page_evictable(page))) { spin_unlock_irq(&zone->lru_lock); putback_lru_page(page); spin_lock_irq(&zone->lru_lock); continue; } lruvec = mem_cgroup_page_lruvec(page, zone); SetPageLRU(page); lru = page_lru(page); add_page_to_lru_list(page, lruvec, 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 (put_page_testzero(page)) { __ClearPageLRU(page); __ClearPageActive(page); del_page_from_lru_list(page, lruvec, lru); if (unlikely(PageCompound(page))) { spin_unlock_irq(&zone->lru_lock); (*get_compound_page_dtor(page))(page); spin_lock_irq(&zone->lru_lock); } else list_add(&page->lru, &pages_to_free); } } /* * To save our caller's stack, now use input list for pages to free. */ list_splice(&pages_to_free, page_list); } /* * 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 lruvec *lruvec, struct scan_control *sc, enum lru_list lru) { LIST_HEAD(page_list); unsigned long nr_scanned; unsigned long nr_reclaimed = 0; unsigned long nr_taken; unsigned long nr_dirty = 0; unsigned long nr_congested = 0; unsigned long nr_unqueued_dirty = 0; unsigned long nr_writeback = 0; unsigned long nr_immediate = 0; isolate_mode_t isolate_mode = 0; int file = is_file_lru(lru); struct zone *zone = lruvec_zone(lruvec); struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 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; } lru_add_drain(); if (!sc->may_unmap) isolate_mode |= ISOLATE_UNMAPPED; if (!sc->may_writepage) isolate_mode |= ISOLATE_CLEAN; spin_lock_irq(&zone->lru_lock); nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list, &nr_scanned, sc, isolate_mode, lru); __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken); __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken); if (global_reclaim(sc)) { 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); } spin_unlock_irq(&zone->lru_lock); if (nr_taken == 0) return 0; nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP, &nr_dirty, &nr_unqueued_dirty, &nr_congested, &nr_writeback, &nr_immediate, false); spin_lock_irq(&zone->lru_lock); reclaim_stat->recent_scanned[file] += nr_taken; if (global_reclaim(sc)) { if (current_is_kswapd()) __count_zone_vm_events(PGSTEAL_KSWAPD, zone, nr_reclaimed); else __count_zone_vm_events(PGSTEAL_DIRECT, zone, nr_reclaimed); } putback_inactive_pages(lruvec, &page_list); __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken); spin_unlock_irq(&zone->lru_lock); free_hot_cold_page_list(&page_list, 1); /* * If reclaim is isolating dirty pages under writeback, it implies * that the long-lived page allocation rate is exceeding the page * laundering rate. Either the global limits are not being effective * at throttling processes due to the page distribution throughout * zones or there is heavy usage of a slow backing device. The * only option is to throttle from reclaim context which is not ideal * as there is no guarantee the dirtying process is throttled in the * same way balance_dirty_pages() manages. * * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number * of pages under pages flagged for immediate reclaim and stall if any * are encountered in the nr_immediate check below. */ if (nr_writeback && nr_writeback == nr_taken) zone_set_flag(zone, ZONE_WRITEBACK); /* * memcg will stall in page writeback so only consider forcibly * stalling for global reclaim */ if (global_reclaim(sc)) { /* * Tag a zone as congested if all the dirty pages scanned were * backed by a congested BDI and wait_iff_congested will stall. */ if (nr_dirty && nr_dirty == nr_congested) zone_set_flag(zone, ZONE_CONGESTED); /* * If dirty pages are scanned that are not queued for IO, it * implies that flushers are not keeping up. In this case, flag * the zone ZONE_TAIL_LRU_DIRTY and kswapd will start writing * pages from reclaim context. It will forcibly stall in the * next check. */ if (nr_unqueued_dirty == nr_taken) zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY); /* * In addition, if kswapd scans pages marked marked for * immediate reclaim and under writeback (nr_immediate), it * implies that pages are cycling through the LRU faster than * they are written so also forcibly stall. */ if (nr_unqueued_dirty == nr_taken || nr_immediate) congestion_wait(BLK_RW_ASYNC, HZ/10); } /* * Stall direct reclaim for IO completions if underlying BDIs or zone * is congested. Allow kswapd to continue until it starts encountering * unqueued dirty pages or cycling through the LRU too quickly. */ if (!sc->hibernation_mode && !current_is_kswapd()) wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10); trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id, zone_idx(zone), nr_scanned, nr_reclaimed, sc->priority, trace_shrink_flags(file)); 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 lruvec *lruvec, struct list_head *list, struct list_head *pages_to_free, enum lru_list lru) { struct zone *zone = lruvec_zone(lruvec); unsigned long pgmoved = 0; struct page *page; int nr_pages; while (!list_empty(list)) { page = lru_to_page(list); lruvec = mem_cgroup_page_lruvec(page, zone); VM_BUG_ON(PageLRU(page)); SetPageLRU(page); nr_pages = hpage_nr_pages(page); mem_cgroup_update_lru_size(lruvec, lru, nr_pages); list_move(&page->lru, &lruvec->lists[lru]); pgmoved += nr_pages; if (put_page_testzero(page)) { __ClearPageLRU(page); __ClearPageActive(page); del_page_from_lru_list(page, lruvec, lru); if (unlikely(PageCompound(page))) { spin_unlock_irq(&zone->lru_lock); (*get_compound_page_dtor(page))(page); spin_lock_irq(&zone->lru_lock); } else list_add(&page->lru, pages_to_free); } } __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_to_scan, struct lruvec *lruvec, struct scan_control *sc, enum lru_list lru) { unsigned long nr_taken; unsigned long nr_scanned; 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 = &lruvec->reclaim_stat; unsigned long nr_rotated = 0; isolate_mode_t isolate_mode = 0; int file = is_file_lru(lru); struct zone *zone = lruvec_zone(lruvec); lru_add_drain(); if (!sc->may_unmap) isolate_mode |= ISOLATE_UNMAPPED; if (!sc->may_writepage) isolate_mode |= ISOLATE_CLEAN; spin_lock_irq(&zone->lru_lock); nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold, &nr_scanned, sc, isolate_mode, lru); if (global_reclaim(sc)) zone->pages_scanned += nr_scanned; reclaim_stat->recent_scanned[file] += nr_taken; __count_zone_vm_events(PGREFILL, zone, nr_scanned); __mod_zone_page_state(zone, NR_LRU_BASE + lru, -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))) { putback_lru_page(page); continue; } if (unlikely(buffer_heads_over_limit)) { if (page_has_private(page) && trylock_page(page)) { if (page_has_private(page)) try_to_release_page(page, 0); unlock_page(page); } } if (page_referenced(page, 0, sc->target_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(lruvec, &l_active, &l_hold, lru); move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE); __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken); spin_unlock_irq(&zone->lru_lock); free_hot_cold_page_list(&l_hold, 1); } #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 * @lruvec: LRU vector to check * * 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 lruvec *lruvec) { /* * If we don't have swap space, anonymous page deactivation * is pointless. */ if (!total_swap_pages) return 0; if (!mem_cgroup_disabled()) return mem_cgroup_inactive_anon_is_low(lruvec); return inactive_anon_is_low_global(lruvec_zone(lruvec)); } #else static inline int inactive_anon_is_low(struct lruvec *lruvec) { return 0; } #endif /** * inactive_file_is_low - check if file pages need to be deactivated * @lruvec: LRU vector to check * * 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 lruvec *lruvec) { unsigned long inactive; unsigned long active; inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE); active = get_lru_size(lruvec, LRU_ACTIVE_FILE); return active > inactive; } static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru) { if (is_file_lru(lru)) return inactive_file_is_low(lruvec); else return inactive_anon_is_low(lruvec); } static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan, struct lruvec *lruvec, struct scan_control *sc) { if (is_active_lru(lru)) { if (inactive_list_is_low(lruvec, lru)) shrink_active_list(nr_to_scan, lruvec, sc, lru); return 0; } return shrink_inactive_list(nr_to_scan, lruvec, sc, lru); } static int vmscan_swappiness(struct scan_control *sc) { if (global_reclaim(sc)) return vm_swappiness; return mem_cgroup_swappiness(sc->target_mem_cgroup); } enum scan_balance { SCAN_EQUAL, SCAN_FRACT, SCAN_ANON, SCAN_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 inactive pages to scan; nr[1] = anon active pages to scan * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan */ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, unsigned long *nr) { struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; u64 fraction[2]; u64 denominator = 0; /* gcc */ struct zone *zone = lruvec_zone(lruvec); unsigned long anon_prio, file_prio; enum scan_balance scan_balance; unsigned long anon, file, free; bool force_scan = false; unsigned long ap, fp; enum lru_list lru; /* * If the zone or memcg is small, nr[l] can be 0. This * results in no scanning on this priority and a potential * priority drop. Global direct reclaim can go to the next * zone and tends to have no problems. Global kswapd is for * zone balancing and it needs to scan a minimum amount. When * reclaiming for a memcg, a priority drop can cause high * latencies, so it's better to scan a minimum amount there as * well. */ if (current_is_kswapd() && !zone_reclaimable(zone)) force_scan = true; if (!global_reclaim(sc)) force_scan = true; /* If we have no swap space, do not bother scanning anon pages. */ if (!sc->may_swap || (get_nr_swap_pages() <= 0)) { scan_balance = SCAN_FILE; goto out; } /* * Global reclaim will swap to prevent OOM even with no * swappiness, but memcg users want to use this knob to * disable swapping for individual groups completely when * using the memory controller's swap limit feature would be * too expensive. */ if (!global_reclaim(sc) && !vmscan_swappiness(sc)) { scan_balance = SCAN_FILE; goto out; } /* * Do not apply any pressure balancing cleverness when the * system is close to OOM, scan both anon and file equally * (unless the swappiness setting disagrees with swapping). */ if (!sc->priority && vmscan_swappiness(sc)) { scan_balance = SCAN_EQUAL; goto out; } anon = get_lru_size(lruvec, LRU_ACTIVE_ANON) + get_lru_size(lruvec, LRU_INACTIVE_ANON); file = get_lru_size(lruvec, LRU_ACTIVE_FILE) + get_lru_size(lruvec, LRU_INACTIVE_FILE); /* * If it's foreseeable that reclaiming the file cache won't be * enough to get the zone back into a desirable shape, we have * to swap. Better start now and leave the - probably heavily * thrashing - remaining file pages alone. */ if (global_reclaim(sc)) { free = zone_page_state(zone, NR_FREE_PAGES); if (unlikely(file + free <= high_wmark_pages(zone))) { scan_balance = SCAN_ANON; goto out; } } /* * There is enough inactive page cache, do not reclaim * anything from the anonymous working set right now. */ if (!inactive_file_is_low(lruvec)) { scan_balance = SCAN_FILE; goto out; } scan_balance = SCAN_FRACT; /* * With swappiness at 100, anonymous and file have the same priority. * This scanning priority is essentially the inverse of IO cost. */ anon_prio = vmscan_swappiness(sc); file_prio = 200 - anon_prio; /* * 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 * (reclaim_stat->recent_scanned[0] + 1); ap /= reclaim_stat->recent_rotated[0] + 1; fp = file_prio * (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; out: for_each_evictable_lru(lru) { int file = is_file_lru(lru); unsigned long size; unsigned long scan; size = get_lru_size(lruvec, lru); scan = size >> sc->priority; if (!scan && force_scan) scan = min(size, SWAP_CLUSTER_MAX); switch (scan_balance) { case SCAN_EQUAL: /* Scan lists relative to size */ break; case SCAN_FRACT: /* * Scan types proportional to swappiness and * their relative recent reclaim efficiency. */ scan = div64_u64(scan * fraction[file], denominator); break; case SCAN_FILE: case SCAN_ANON: /* Scan one type exclusively */ if ((scan_balance == SCAN_FILE) != file) scan = 0; break; default: /* Look ma, no brain */ BUG(); } nr[lru] = scan; } } /* * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. */ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) { unsigned long nr[NR_LRU_LISTS]; unsigned long targets[NR_LRU_LISTS]; unsigned long nr_to_scan; enum lru_list lru; unsigned long nr_reclaimed = 0; unsigned long nr_to_reclaim = sc->nr_to_reclaim; struct blk_plug plug; bool scan_adjusted = false; get_scan_count(lruvec, sc, nr); /* Record the original scan target for proportional adjustments later */ memcpy(targets, nr, sizeof(nr)); blk_start_plug(&plug); while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || nr[LRU_INACTIVE_FILE]) { unsigned long nr_anon, nr_file, percentage; unsigned long nr_scanned; for_each_evictable_lru(lru) { if (nr[lru]) { nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX); nr[lru] -= nr_to_scan; nr_reclaimed += shrink_list(lru, nr_to_scan, lruvec, sc); } } if (nr_reclaimed < nr_to_reclaim || scan_adjusted) continue; /* * For global direct reclaim, reclaim only the number of pages * requested. Less care is taken to scan proportionally as it * is more important to minimise direct reclaim stall latency * than it is to properly age the LRU lists. */ if (global_reclaim(sc) && !current_is_kswapd()) break; /* * For kswapd and memcg, reclaim at least the number of pages * requested. Ensure that the anon and file LRUs shrink * proportionally what was requested by get_scan_count(). We * stop reclaiming one LRU and reduce the amount scanning * proportional to the original scan target. */ nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE]; nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON]; if (nr_file > nr_anon) { unsigned long scan_target = targets[LRU_INACTIVE_ANON] + targets[LRU_ACTIVE_ANON] + 1; lru = LRU_BASE; percentage = nr_anon * 100 / scan_target; } else { unsigned long scan_target = targets[LRU_INACTIVE_FILE] + targets[LRU_ACTIVE_FILE] + 1; lru = LRU_FILE; percentage = nr_file * 100 / scan_target; } /* Stop scanning the smaller of the LRU */ nr[lru] = 0; nr[lru + LRU_ACTIVE] = 0; /* * Recalculate the other LRU scan count based on its original * scan target and the percentage scanning already complete */ lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE; nr_scanned = targets[lru] - nr[lru]; nr[lru] = targets[lru] * (100 - percentage) / 100; nr[lru] -= min(nr[lru], nr_scanned); lru += LRU_ACTIVE; nr_scanned = targets[lru] - nr[lru]; nr[lru] = targets[lru] * (100 - percentage) / 100; nr[lru] -= min(nr[lru], nr_scanned); scan_adjusted = true; } blk_finish_plug(&plug); 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(lruvec)) shrink_active_list(SWAP_CLUSTER_MAX, lruvec, sc, LRU_ACTIVE_ANON); throttle_vm_writeout(sc->gfp_mask); } /* Use reclaim/compaction for costly allocs or under memory pressure */ static bool in_reclaim_compaction(struct scan_control *sc) { if (IS_ENABLED(CONFIG_COMPACTION) && sc->order && (sc->order > PAGE_ALLOC_COSTLY_ORDER || sc->priority < DEF_PRIORITY - 2)) return true; return false; } /* * Reclaim/compaction is used for high-order allocation requests. It reclaims * order-0 pages before compacting the zone. should_continue_reclaim() returns * true if more pages should be reclaimed such that when the page allocator * calls try_to_compact_zone() that it will have enough free pages to succeed. * It will give up earlier than that if there is difficulty reclaiming pages. */ 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 (!in_reclaim_compaction(sc)) 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_page_state(zone, NR_INACTIVE_FILE); if (get_nr_swap_pages() > 0) inactive_lru_pages += zone_page_state(zone, NR_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; } } static void shrink_zone(struct zone *zone, struct scan_control *sc) { unsigned long nr_reclaimed, nr_scanned; do { struct mem_cgroup *root = sc->target_mem_cgroup; struct mem_cgroup_reclaim_cookie reclaim = { .zone = zone, .priority = sc->priority, }; struct mem_cgroup *memcg; nr_reclaimed = sc->nr_reclaimed; nr_scanned = sc->nr_scanned; memcg = mem_cgroup_iter(root, NULL, &reclaim); do { struct lruvec *lruvec; lruvec = mem_cgroup_zone_lruvec(zone, memcg); shrink_lruvec(lruvec, sc); /* * Direct reclaim and kswapd have to scan all memory * cgroups to fulfill the overall scan target for the * zone. * * Limit reclaim, on the other hand, only cares about * nr_to_reclaim pages to be reclaimed and it will * retry with decreasing priority if one round over the * whole hierarchy is not sufficient. */ if (!global_reclaim(sc) && sc->nr_reclaimed >= sc->nr_to_reclaim) { mem_cgroup_iter_break(root, memcg); break; } memcg = mem_cgroup_iter(root, memcg, &reclaim); } while (memcg); vmpressure(sc->gfp_mask, sc->target_mem_cgroup, sc->nr_scanned - nr_scanned, sc->nr_reclaimed - nr_reclaimed); } while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed, sc->nr_scanned - nr_scanned, sc)); } /* 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->managed_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, sc->order)) 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 indicat