diff options
Diffstat (limited to 'mm/vmscan.c')
| -rw-r--r-- | mm/vmscan.c | 3847 |
1 files changed, 3847 insertions, 0 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c new file mode 100644 index 000000000..dd544baec --- /dev/null +++ b/mm/vmscan.c @@ -0,0 +1,3847 @@ +/* + * 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. + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/mm.h> +#include <linux/module.h> +#include <linux/gfp.h> +#include <linux/kernel_stat.h> +#include <linux/swap.h> +#include <linux/pagemap.h> +#include <linux/init.h> +#include <linux/highmem.h> +#include <linux/vmpressure.h> +#include <linux/vmstat.h> +#include <linux/file.h> +#include <linux/writeback.h> +#include <linux/blkdev.h> +#include <linux/buffer_head.h> /* for try_to_release_page(), + buffer_heads_over_limit */ +#include <linux/mm_inline.h> +#include <linux/backing-dev.h> +#include <linux/rmap.h> +#include <linux/topology.h> +#include <linux/cpu.h> +#include <linux/cpuset.h> +#include <linux/compaction.h> +#include <linux/notifier.h> +#include <linux/rwsem.h> +#include <linux/delay.h> +#include <linux/kthread.h> +#include <linux/freezer.h> +#include <linux/memcontrol.h> +#include <linux/delayacct.h> +#include <linux/sysctl.h> +#include <linux/oom.h> +#include <linux/prefetch.h> +#include <linux/printk.h> + +#include <asm/tlbflush.h> +#include <asm/div64.h> + +#include <linux/swapops.h> +#include <linux/balloon_compaction.h> + +#include "internal.h" + +#define CREATE_TRACE_POINTS +#include <trace/events/vmscan.h> + +struct scan_control { + /* How many pages shrink_list() should reclaim */ + unsigned long nr_to_reclaim; + + /* This context's GFP mask */ + gfp_t gfp_mask; + + /* Allocation order */ + int order; + + /* + * Nodemask of nodes allowed by the caller. If NULL, all nodes + * are scanned. + */ + nodemask_t *nodemask; + + /* + * 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; + + /* Scan (total_size >> priority) pages at once */ + int priority; + + unsigned int may_writepage:1; + + /* Can mapped pages be reclaimed? */ + unsigned int may_unmap:1; + + /* Can pages be swapped as part of reclaim? */ + unsigned int may_swap:1; + + /* Can cgroups be reclaimed below their normal consumption range? */ + unsigned int may_thrash:1; + + unsigned int hibernation_mode:1; + + /* One of the zones is ready for compaction */ + unsigned int compaction_ready:1; + + /* 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; +}; + +#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; +/* + * The total number of pages which are beyond the high watermark within all + * zones. + */ +unsigned long vm_total_pages; + +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 + +static 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_page_state(zone, NR_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); + kfree(shrinker->nr_deferred); +} +EXPORT_SYMBOL(unregister_shrinker); + +#define SHRINK_BATCH 128 + +static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, + struct shrinker *shrinker, + unsigned long nr_scanned, + unsigned long nr_eligible) +{ + unsigned long freed = 0; + unsigned long long delta; + long total_scan; + long freeable; + long nr; + long new_nr; + int nid = shrinkctl->nid; + long batch_size = shrinker->batch ? shrinker->batch + : SHRINK_BATCH; + + freeable = shrinker->count_objects(shrinker, shrinkctl); + if (freeable == 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_scanned) / shrinker->seeks; + delta *= freeable; + do_div(delta, nr_eligible + 1); + total_scan += delta; + if (total_scan < 0) { + pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n", + shrinker->scan_objects, total_scan); + total_scan = freeable; + } + + /* + * 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 >>> + * freeable. 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 < freeable / 4) + total_scan = min(total_scan, freeable / 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 > freeable * 2) + total_scan = freeable * 2; + + trace_mm_shrink_slab_start(shrinker, shrinkctl, nr, + nr_scanned, nr_eligible, + freeable, delta, total_scan); + + /* + * Normally, we should not scan less than batch_size objects in one + * pass to avoid too frequent shrinker calls, but if the slab has less + * than batch_size objects in total and we are really tight on memory, + * we will try to reclaim all available objects, otherwise we can end + * up failing allocations although there are plenty of reclaimable + * objects spread over several slabs with usage less than the + * batch_size. + * + * We detect the "tight on memory" situations by looking at the total + * number of objects we want to scan (total_scan). If it is greater + * than the total number of objects on slab (freeable), we must be + * scanning at high prio and therefore should try to reclaim as much as + * possible. + */ + while (total_scan >= batch_size || + total_scan >= freeable) { + unsigned long ret; + unsigned long nr_to_scan = min(batch_size, total_scan); + + shrinkctl->nr_to_scan = nr_to_scan; + ret = shrinker->scan_objects(shrinker, shrinkctl); + if (ret == SHRINK_STOP) + break; + freed += ret; + + count_vm_events(SLABS_SCANNED, nr_to_scan); + total_scan -= nr_to_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. + */ + 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, nid, freed, nr, new_nr, total_scan); + return freed; +} + +/** + * shrink_slab - shrink slab caches + * @gfp_mask: allocation context + * @nid: node whose slab caches to target + * @memcg: memory cgroup whose slab caches to target + * @nr_scanned: pressure numerator + * @nr_eligible: pressure denominator + * + * Call the shrink functions to age shrinkable caches. + * + * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set, + * unaware shrinkers will receive a node id of 0 instead. + * + * @memcg specifies the memory cgroup to target. If it is not NULL, + * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan + * objects from the memory cgroup specified. Otherwise all shrinkers + * are called, and memcg aware shrinkers are supposed to scan the + * global list then. + * + * @nr_scanned and @nr_eligible form a ratio that indicate how much of + * the available objects should be scanned. Page reclaim for example + * passes the number of pages scanned and the number of pages on the + * LRU lists that it considered on @nid, plus a bias in @nr_scanned + * when it encountered mapped pages. The ratio is further biased by + * the ->seeks setting of the shrink function, which indicates the + * cost to recreate an object relative to that of an LRU page. + * + * Returns the number of reclaimed slab objects. + */ +static unsigned long shrink_slab(gfp_t gfp_mask, int nid, + struct mem_cgroup *memcg, + unsigned long nr_scanned, + unsigned long nr_eligible) +{ + struct shrinker *shrinker; + unsigned long freed = 0; + + if (memcg && !memcg_kmem_is_active(memcg)) + return 0; + + if (nr_scanned == 0) + nr_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) { + struct shrink_control sc = { + .gfp_mask = gfp_mask, + .nid = nid, + .memcg = memcg, + }; + + if (memcg && !(shrinker->flags & SHRINKER_MEMCG_AWARE)) + continue; + + if (!(shrinker->flags & SHRINKER_NUMA_AWARE)) + sc.nid = 0; + + freed += do_shrink_slab(&sc, shrinker, nr_scanned, nr_eligible); + } + + up_read(&shrinker_rwsem); +out: + cond_resched(); + return freed; +} + +void drop_slab_node(int nid) +{ + unsigned long freed; + + do { + struct mem_cgroup *memcg = NULL; + + freed = 0; + do { + freed += shrink_slab(GFP_KERNEL, nid, memcg, + 1000, 1000); + } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL); + } while (freed > 10); +} + +void drop_slab(void) +{ + int nid; + + for_each_online_node(nid) + drop_slab_node(nid); +} + +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_write_iter() 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); + pr_info("%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(inode_to_bdi(mapping->host), 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, + bool reclaimed) +{ + 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) }; + mem_cgroup_swapout(page, swap); + __delete_from_swap_cache(page); + spin_unlock_irq(&mapping->tree_lock); + swapcache_free(swap); + } else { + void (*freepage)(struct page *); + void *shadow = NULL; + + freepage = mapping->a_ops->freepage; + /* + * Remember a shadow entry for reclaimed file cache in + * order to detect refaults, thus thrashing, later on. + * + * But don't store shadows in an address space that is + * already exiting. This is not just an optizimation, + * inode reclaim needs to empty out the radix tree or + * the nodes are lost. Don't plant shadows behind its + * back. + */ + if (reclaimed && page_is_file_cache(page) && + !mapping_exiting(mapping)) + shadow = workingset_eviction(mapping, page); + __delete_from_page_cache(page, shadow); + spin_unlock_irq(&mapping->tree_lock); + + 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, false)) { + /* + * 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_PAGE(PageLRU(page), 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(); + + 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_PAGE(PageActive(page), page); + VM_BUG_ON_PAGE(page_zone(page) != zone, page); + + 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 (((dirty || writeback) && mapping && + bdi_write_congested(inode_to_bdi(mapping->host))) || + (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) && + test_bit(ZONE_WRITEBACK, &zone->flags)) { + 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() || + !test_bit(ZONE_DIRTY, &zone->flags))) { + /* + * 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, true)) + 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_PAGE(PageActive(page), page); + SetPageActive(page); + pgactivate++; +keep_locked: + unlock_page(page); +keep: + list_add(&page->lru, &ret_pages); + VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page); + } + + mem_cgroup_uncharge_list(&free_pages); + free_hot_cold_page_list(&free_pages, true); + + list_splice(&ret_pages, page_list); + count_vm_events(PGACTIVATE, pgactivate); + + *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_PAGE(!PageLRU(page), 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(!page_count(page), 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() || sc->hibernation_mode) + 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_PAGE(PageLRU(page), 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); + mem_cgroup_uncharge(page); + (*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); +} + +/* + * If a kernel thread (such as nfsd for loop-back mounts) services + * a backing device by writing to the page cache it sets PF_LESS_THROTTLE. + * In that case we should only throttle if the backing device it is + * writing to is congested. In other cases it is safe to throttle. + */ +static int current_may_throttle(void) +{ + return !(current->flags & PF_LESS_THROTTLE) || + current->backing_dev_info == NULL || + bdi_write_congested(current->backing_dev_info); +} + +/* + * 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)) { + __mod_zone_page_state(zone, NR_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); + + mem_cgroup_uncharge_list(&page_list); + free_hot_cold_page_list(&page_list, true); + + /* + * 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) + set_bit(ZONE_WRITEBACK, &zone->flags); + + /* + * 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) + set_bit(ZONE_CONGESTED, &zone->flags); + + /* + * 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_DIRTY and kswapd will start writing pages from + * reclaim context. + */ + if (nr_unqueued_dirty == nr_taken) + set_bit(ZONE_DIRTY, &zone->flags); + + /* + * 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_immediate && current_may_throttle()) + 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() && + current_may_throttle()) + 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_PAGE(PageLRU(page), 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); + mem_cgroup_uncharge(page); + (*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)) + __mod_zone_page_state(zone, NR_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_count. + */ + 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); + + mem_cgroup_uncharge_list(&l_hold); + free_hot_cold_page_list(&l_hold, true); +} + +#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); +} + +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, int swappiness, + struct scan_control *sc, unsigned long *nr, + unsigned long *lru_pages) +{ + 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; + bool force_scan = false; + unsigned long ap, fp; + enum lru_list lru; + bool some_scanned; + int pass; + + /* + * 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()) { + if (!zone_reclaimable(zone)) + force_scan = true; + if (!mem_cgroup_lruvec_online(lruvec)) + 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) && !swappiness) { + 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 && swappiness) { + scan_balance = SCAN_EQUAL; + goto out; + } + + /* + * Prevent the reclaimer from falling into the cache trap: as + * cache pages start out inactive, every cache fault will tip + * the scan balance towards the file LRU. And as the file LRU + * shrinks, so does the window for rotation from references. + * This means we have a runaway feedback loop where a tiny + * thrashing file LRU becomes infinitely more attractive than + * anon pages. Try to detect this based on file LRU size. + */ + if (global_reclaim(sc)) { + unsigned long zonefile; + unsigned long zonefree; + + zonefree = zone_page_state(zone, NR_FREE_PAGES); + zonefile = zone_page_state(zone, NR_ACTIVE_FILE) + + zone_page_state(zone, NR_INACTIVE_FILE); + + if (unlikely(zonefile + zonefree <= 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 = swappiness; + 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] + */ + + 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); + + 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: + some_scanned = false; + /* Only use force_scan on second pass. */ + for (pass = 0; !some_scanned && pass < 2; pass++) { + *lru_pages = 0; + 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 && pass && 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) { + size = 0; + scan = 0; + } + break; + default: + /* Look ma, no brain */ + BUG(); + } + + *lru_pages += size; + nr[lru] = scan; + + /* + * Skip the second pass and don't force_scan, + * if we found something to scan. + */ + some_scanned |= !!scan; + } + } +} + +/* + * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. + */ +static void shrink_lruvec(struct lruvec *lruvec, int swappiness, + struct scan_control *sc, unsigned long *lru_pages) +{ + 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; + + get_scan_count(lruvec, swappiness, sc, nr, lru_pages); + + /* Record the original scan target for proportional adjustments later */ + memcpy(targets, nr, sizeof(nr)); + + /* + * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal + * event that can occur when there is little memory pressure e.g. + * multiple streaming readers/writers. Hence, we do not abort scanning + * when the requested number of pages are reclaimed when scanning at + * DEF_PRIORITY on the assumption that the fact we are direct + * reclaiming implies that kswapd is not keeping up and it is best to + * do a batch of work at once. For memcg reclaim one check is made to + * abort proportional reclaim if either the file or anon lru has already + * dropped to zero at the first pass. + */ + scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() && + sc->priority == DEF_PRIORITY); + + 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 kswapd and memcg, reclaim at least the number of pages + * requested. Ensure that the anon and file LRUs are scanned + * 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]; + + /* + * It's just vindictive to attack the larger once the smaller + * has gone to zero. And given the way we stop scanning the + * smaller below, this makes sure that we only make one nudge + * towards proportionality once we've got nr_to_reclaim. + */ + if (!nr_file || !nr_anon) + break; + + 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 (nr_reclaimed && nr_scanned && sc->nr_to_reclaim >= sc->nr_reclaimed) + return true; + + /* 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, 0, 0)) { + case COMPACT_PARTIAL: + case COMPACT_CONTINUE: + return false; + default: + return true; + } +} + +static bool shrink_zone(struct zone *zone, struct scan_control *sc, + bool is_classzone) +{ + struct reclaim_state *reclaim_state = current->reclaim_state; + unsigned long nr_reclaimed, nr_scanned; + bool reclaimable = false; + + do { + struct mem_cgroup *root = sc->target_mem_cgroup; + struct mem_cgroup_reclaim_cookie reclaim = { + .zone = zone, + .priority = sc->priority, + }; + unsigned long zone_lru_pages = 0; + struct mem_cgroup *memcg; + + nr_reclaimed = sc->nr_reclaimed; + nr_scanned = sc->nr_scanned; + + memcg = mem_cgroup_iter(root, NULL, &reclaim); + do { + unsigned long lru_pages; + unsigned long scanned; + struct lruvec *lruvec; + int swappiness; + + if (mem_cgroup_low(root, memcg)) { + if (!sc->may_thrash) + continue; + mem_cgroup_events(memcg, MEMCG_LOW, 1); + } + + lruvec = mem_cgroup_zone_lruvec(zone, memcg); + swappiness = mem_cgroup_swappiness(memcg); + scanned = sc->nr_scanned; + + shrink_lruvec(lruvec, swappiness, sc, &lru_pages); + zone_lru_pages += lru_pages; + + if (memcg && is_classzone) + shrink_slab(sc->gfp_mask, zone_to_nid(zone), + memcg, sc->nr_scanned - scanned, + lru_pages); + + /* + * 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; + } + } while ((memcg = mem_cgroup_iter(root, memcg, &reclaim))); + + /* + * Shrink the slab caches in the same proportion that + * the eligible LRU pages were scanned. + */ + if (global_reclaim(sc) && is_classzone) + shrink_slab(sc->gfp_mask, zone_to_nid(zone), NULL, + sc->nr_scanned - nr_scanned, + zone_lru_pages); + + if (reclaim_state) { + sc->nr_reclaimed += reclaim_state->reclaimed_slab; + reclaim_state->reclaimed_slab = 0; + } + + vmpressure(sc->gfp_mask, sc->target_mem_cgroup, + sc->nr_scanned - nr_scanned, + sc->nr_reclaimed - nr_reclaimed); + + if (sc->nr_reclaimed - nr_reclaimed) + reclaimable = true; + + } while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed, + sc->nr_scanned - nr_scanned, sc)); + + return reclaimable; +} + +/* + * Returns true if compaction should go ahead for a high-order request, or + * the high-order allocation would succeed without compaction. + */ +static inline bool compaction_ready(struct zone *zone, int order) +{ + unsigned long balance_gap, watermark; + bool watermark_ok; + + /* + * 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), DIV_ROUND_UP( + zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO)); + watermark = high_wmark_pages(zone) + balance_gap + (2UL << 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, order)) + return watermark_ok; + + /* + * If compaction is not ready to start and allocation is not likely + * to succeed without it, then keep reclaiming. + */ + if (compaction_suitable(zone, order, 0, 0) == COMPACT_SKIPPED) + 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. + * + * Returns true if a zone was reclaimable. + */ +static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc) +{ + struct zoneref *z; + struct zone *zone; + unsigned long nr_soft_reclaimed; + unsigned long nr_soft_scanned; + gfp_t orig_mask; + enum zone_type requested_highidx = gfp_zone(sc->gfp_mask); + bool reclaimable = false; + + /* + * If the number of buffer_heads in the machine exceeds the maximum + * allowed level, force direct reclaim to scan the highmem zone as + * highmem pages could be pinning lowmem pages storing buffer_heads + */ + orig_mask = sc->gfp_mask; + if (buffer_heads_over_limit) + sc->gfp_mask |= __GFP_HIGHMEM; + + for_each_zone_zonelist_nodemask(zone, z, zonelist, + requested_highidx, sc->nodemask) { + enum zone_type classzone_idx; + + if (!populated_zone(zone)) + continue; + + classzone_idx = requested_highidx; + while (!populated_zone(zone->zone_pgdat->node_zones + + classzone_idx)) + classzone_idx--; + + /* + * Take care memory controller reclaiming has small influence + * to global LRU. + */ + if (global_reclaim(sc)) { + if (!cpuset_zone_allowed(zone, + GFP_KERNEL | __GFP_HARDWALL)) + continue; + + if (sc->priority != DEF_PRIORITY && + !zone_reclaimable(zone)) + continue; /* Let kswapd poll it */ + + /* + * 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 + * noticeable problem, like transparent huge + * page allocations. + */ + if (IS_ENABLED(CONFIG_COMPACTION) && + sc->order > PAGE_ALLOC_COSTLY_ORDER && + zonelist_zone_idx(z) <= requested_highidx && + compaction_ready(zone, sc->order)) { + sc->compaction_ready = 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; + if (nr_soft_reclaimed) + reclaimable = true; + /* need some check for avoid more shrink_zone() */ + } + + if (shrink_zone(zone, sc, zone_idx(zone) == classzone_idx)) + reclaimable = true; + + if (global_reclaim(sc) && + !reclaimable && zone_reclaimable(zone)) + reclaimable = true; + } + + /* + * Restore to original mask to avoid the impact on the caller if we + * promoted it to __GFP_HIGHMEM. + */ + sc->gfp_mask = orig_mask; + + return reclaimable; +} + +/* + * 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) +{ + int initial_priority = sc->priority; + unsigned long total_scanned = 0; + unsigned long writeback_threshold; + bool zones_reclaimable; + +#ifdef CONFIG_FREEZER + if (unlikely(pm_freezing && !sc->hibernation_mode)) + return 0; +#endif + +retry: + delayacct_freepages_start(); + + if (global_reclaim(sc)) + count_vm_event(ALLOCSTALL); + + do { + vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup, + sc->priority); + sc->nr_scanned = 0; + zones_reclaimable = shrink_zones(zonelist, sc); + + total_scanned += sc->nr_scanned; + if (sc->nr_reclaimed >= sc->nr_to_reclaim) + break; + + if (sc->compaction_ready) + break; + + /* + * If we're getting trouble reclaiming, start doing + * writepage even in laptop mode. + */ + if (sc->priority < DEF_PRIORITY - 2) + sc->may_writepage = 1; + + /* + * 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, + WB_REASON_TRY_TO_FREE_PAGES); + sc->may_writepage = 1; + } + } while (--sc->priority >= 0); + + delayacct_freepages_end(); + + if (sc->nr_reclaimed) + return sc->nr_reclaimed; + + /* Aborted reclaim to try compaction? don't OOM, then */ + if (sc->compaction_ready) + return 1; + + /* Untapped cgroup reserves? Don't OOM, retry. */ + if (!sc->may_thrash) { + sc->priority = initial_priority; + sc->may_thrash = 1; + goto retry; + } + + /* Any of the zones still reclaimable? Don't OOM. */ + if (zones_reclaimable) + return 1; + + return 0; +} + +static bool pfmemalloc_watermark_ok(pg_data_t *pgdat) +{ + struct zone *zone; + unsigned long pfmemalloc_reserve = 0; + unsigned long free_pages = 0; + int i; + bool wmark_ok; + + for (i = 0; i <= ZONE_NORMAL; i++) { + zone = &pgdat->node_zones[i]; + if (!populated_zone(zone)) + continue; + + pfmemalloc_reserve += min_wmark_pages(zone); + free_pages += zone_page_state(zone, NR_FREE_PAGES); + } + + /* If there are no reserves (unexpected config) then do not throttle */ + if (!pfmemalloc_reserve) + return true; + + wmark_ok = free_pages > pfmemalloc_reserve / 2; + + /* kswapd must be awake if processes are being throttled */ + if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) { + pgdat->classzone_idx = min(pgdat->classzone_idx, + (enum zone_type)ZONE_NORMAL); + wake_up_interruptible(&pgdat->kswapd_wait); + } + + return wmark_ok; +} + +/* + * Throttle direct reclaimers if backing storage is backed by the network + * and the PFMEMALLOC reserve for the preferred node is getting dangerously + * depleted. kswapd will continue to make progress and wake the processes + * when the low watermark is reached. + * + * Returns true if a fatal signal was delivered during throttling. If this + * happens, the page allocator should not consider triggering the OOM killer. + */ +static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist, + nodemask_t *nodemask) +{ + struct zoneref *z; + struct zone *zone; + pg_data_t *pgdat = NULL; + + /* + * Kernel threads should not be throttled as they may be indirectly + * responsible for cleaning pages necessary for reclaim to make forward + * progress. kjournald for example may enter direct reclaim while + * committing a transaction where throttling it could forcing other + * processes to block on log_wait_commit(). + */ + if (current->flags & PF_KTHREAD) + goto out; + + /* + * If a fatal signal is pending, this process should not throttle. + * It should return quickly so it can exit and free its memory + */ + if (fatal_signal_pending(current)) + goto out; + + /* + * Check if the pfmemalloc reserves are ok by finding the first node + * with a usable ZONE_NORMAL or lower zone. The expectation is that + * GFP_KERNEL will be required for allocating network buffers when + * swapping over the network so ZONE_HIGHMEM is unusable. + * + * Throttling is based on the first usable node and throttled processes + * wait on a queue until kswapd makes progress and wakes them. There + * is an affinity then between processes waking up and where reclaim + * progress has been made assuming the process wakes on the same node. + * More importantly, processes running on remote nodes will not compete + * for remote pfmemalloc reserves and processes on different nodes + * should make reasonable progress. + */ + for_each_zone_zonelist_nodemask(zone, z, zonelist, + gfp_zone(gfp_mask), nodemask) { + if (zone_idx(zone) > ZONE_NORMAL) + continue; + + /* Throttle based on the first usable node */ + pgdat = zone->zone_pgdat; + if (pfmemalloc_watermark_ok(pgdat)) + goto out; + break; + } + + /* If no zone was usable by the allocation flags then do not throttle */ + if (!pgdat) + goto out; + + /* Account for the throttling */ + count_vm_event(PGSCAN_DIRECT_THROTTLE); + + /* + * If the caller cannot enter the filesystem, it's possible that it + * is due to the caller holding an FS lock or performing a journal + * transaction in the case of a filesystem like ext[3|4]. In this case, + * it is not safe to block on pfmemalloc_wait as kswapd could be + * blocked waiting on the same lock. Instead, throttle for up to a + * second before continuing. + */ + if (!(gfp_mask & __GFP_FS)) { + wait_event_interruptible_timeout(pgdat->pfmemalloc_wait, + pfmemalloc_watermark_ok(pgdat), HZ); + + goto check_pending; + } + + /* Throttle until kswapd wakes the process */ + wait_event_killable(zone->zone_pgdat->pfmemalloc_wait, + pfmemalloc_watermark_ok(pgdat)); + +check_pending: + if (fatal_signal_pending(current)) + return true; + +out: + return false; +} + +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 = { + .nr_to_reclaim = SWAP_CLUSTER_MAX, + .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)), + .order = order, + .nodemask = nodemask, + .priority = DEF_PRIORITY, + .may_writepage = !laptop_mode, + .may_unmap = 1, + .may_swap = 1, + }; + + /* + * Do not enter reclaim if fatal signal was delivered while throttled. + * 1 is returned so that the page allocator does not OOM kill at this + * point. + */ + if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask)) + return 1; + + trace_mm_vmscan_direct_reclaim_begin(order, + sc.may_writepage, + gfp_mask); + + nr_reclaimed = do_try_to_free_pages(zonelist, &sc); + + trace_mm_vmscan_direct_reclaim_end(nr_reclaimed); + + return nr_reclaimed; +} + +#ifdef CONFIG_MEMCG + +unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg, + gfp_t gfp_mask, bool noswap, + struct zone *zone, + unsigned long *nr_scanned) +{ + struct scan_control sc = { + .nr_to_reclaim = SWAP_CLUSTER_MAX, + .target_mem_cgroup = memcg, + .may_writepage = !laptop_mode, + .may_unmap = 1, + .may_swap = !noswap, + }; + struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg); + int swappiness = mem_cgroup_swappiness(memcg); + unsigned long lru_pages; + + sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | + (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK); + + trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order, + 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_lruvec(lruvec, swappiness, &sc, &lru_pages); + + 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 *memcg, + unsigned long nr_pages, + gfp_t gfp_mask, + bool may_swap) +{ + struct zonelist *zonelist; + unsigned long nr_reclaimed; + int nid; + struct scan_control sc = { + .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), + .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | + (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK), + .target_mem_cgroup = memcg, + .priority = DEF_PRIORITY, + .may_writepage = !laptop_mode, + .may_unmap = 1, + .may_swap = may_swap, + }; + + /* + * 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(memcg); + + 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); + + trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed); + + return nr_reclaimed; +} +#endif + +static void age_active_anon(struct zone *zone, struct scan_control *sc) +{ + struct mem_cgroup *memcg; + + if (!total_swap_pages) + return; + + memcg = mem_cgroup_iter(NULL, NULL, NULL); + do { + struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg); + + if (inactive_anon_is_low(lruvec)) + shrink_active_list(SWAP_CLUSTER_MAX, lruvec, + sc, LRU_ACTIVE_ANON); + + memcg = mem_cgroup_iter(NULL, memcg, NULL); + } while (memcg); +} + +static bool zone_balanced(struct zone *zone, int order, + unsigned long balance_gap, int classzone_idx) +{ + if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) + + balance_gap, classzone_idx, 0)) + return false; + + if (IS_ENABLED(CONFIG_COMPACTION) && order && compaction_suitable(zone, + order, 0, classzone_idx) == COMPACT_SKIPPED) + return false; + + return true; +} + +/* + * pgdat_balanced() is used when checking if a node is balanced. + * + * For order-0, all zones must be 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, int order, int classzone_idx) +{ + unsigned long managed_pages = 0; + unsigned long balanced_pages = 0; + int i; + + /* Check the watermark levels */ + for (i = 0; i <= classzone_idx; i++) { + struct zone *zone = pgdat->node_zones + i; + + if (!populated_zone(zone)) + continue; + + managed_pages += zone->managed_pages; + + /* + * A special case here: + * + * balance_pgdat() skips over all_unreclaimable after + * DEF_PRIORITY. Effectively, it considers them balanced so + * they must be considered balanced here as well! + */ + if (!zone_reclaimable(zone)) { + balanced_pages += zone->managed_pages; + continue; + } + + if (zone_balanced(zone, order, 0, i)) + balanced_pages += zone->managed_pages; + else if (!order) + return false; + } + + if (order) + return balanced_pages >= (managed_pages >> 2); + else + return true; +} + +/* + * Prepare kswapd for sleeping. This verifies that there are no processes + * waiting in throttle_direct_reclaim() and that watermarks have been met. + * + * Returns true if kswapd is ready to sleep + */ +static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining, + int classzone_idx) +{ + /* If a direct reclaimer woke kswapd within HZ/10, it's premature */ + if (remaining) + return false; + + /* + * The throttled processes are normally woken up in balance_pgdat() as + * soon as pfmemalloc_watermark_ok() is true. But there is a potential + * race between when kswapd checks the watermarks and a process gets + * throttled. There is also a potential race if processes get + * throttled, kswapd wakes, a large process exits thereby balancing the + * zones, which causes kswapd to exit balance_pgdat() before reaching + * the wake up checks. If kswapd is going to sleep, no process should + * be sleeping on pfmemalloc_wait, so wake them now if necessary. If + * the wake up is premature, processes will wake kswapd and get + * throttled again. The difference from wake ups in balance_pgdat() is + * that here we are under prepare_to_wait(). + */ + if (waitqueue_active(&pgdat->pfmemalloc_wait)) + wake_up_all(&pgdat->pfmemalloc_wait); + + return pgdat_balanced(pgdat, order, classzone_idx); +} + +/* + * kswapd shrinks the zone by the number of pages required to reach + * the high watermark. + * + * Returns true if kswapd scanned at least the requested number of pages to + * reclaim or if the lack of progress was due to pages under writeback. + * This is used to determine if the scanning priority needs to be raised. + */ +static bool kswapd_shrink_zone(struct zone *zone, + int classzone_idx, + struct scan_control *sc, + unsigned long *nr_attempted) +{ + int testorder = sc->order; + unsigned long balance_gap; + bool lowmem_pressure; + + /* Reclaim above the high watermark. */ + sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone)); + + /* + * Kswapd reclaims only single pages with compaction enabled. Trying + * too hard to reclaim until contiguous free pages have become + * available can hurt performance by evicting too much useful data + * from memory. Do not reclaim more than needed for compaction. + */ + if (IS_ENABLED(CONFIG_COMPACTION) && sc->order && + compaction_suitable(zone, sc->order, 0, classzone_idx) + != COMPACT_SKIPPED) + testorder = 0; + + /* + * 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), DIV_ROUND_UP( + zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO)); + + /* + * If there is no low memory pressure or the zone is balanced then no + * reclaim is necessary + */ + lowmem_pressure = (buffer_heads_over_limit && is_highmem(zone)); + if (!lowmem_pressure && zone_balanced(zone, testorder, + balance_gap, classzone_idx)) + return true; + + shrink_zone(zone, sc, zone_idx(zone) == classzone_idx); + + /* Account for the number of pages attempted to reclaim */ + *nr_attempted += sc->nr_to_reclaim; + + clear_bit(ZONE_WRITEBACK, &zone->flags); + + /* + * 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, speculatively avoid congestion + * waits. + */ + if (zone_reclaimable(zone) && + zone_balanced(zone, testorder, 0, classzone_idx)) { + clear_bit(ZONE_CONGESTED, &zone->flags); + clear_bit(ZONE_DIRTY, &zone->flags); + } + + return sc->nr_scanned >= sc->nr_to_reclaim; +} + +/* + * 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 i; + int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ + unsigned long nr_soft_reclaimed; + unsigned long nr_soft_scanned; + struct scan_control sc = { + .gfp_mask = GFP_KERNEL, + .order = order, + .priority = DEF_PRIORITY, + .may_writepage = !laptop_mode, + .may_unmap = 1, + .may_swap = 1, + }; + count_vm_event(PAGEOUTRUN); + + do { + unsigned long nr_attempted = 0; + bool raise_priority = true; + bool pgdat_needs_compaction = (order > 0); + + sc.nr_reclaimed = 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 (sc.priority != DEF_PRIORITY && + !zone_reclaimable(zone)) + continue; + + /* + * Do some background aging of the anon list, to give + * pages a chance to be referenced before reclaiming. + */ + age_active_anon(zone, &sc); + + /* + * If the number of buffer_heads in the machine + * exceeds the maximum allowed level and this node + * has a highmem zone, force kswapd to reclaim from + * it to relieve lowmem pressure. + */ + if (buffer_heads_over_limit && is_highmem_idx(i)) { + end_zone = i; + break; + } + + if (!zone_balanced(zone, order, 0, 0)) { + end_zone = i; + break; + } else { + /* + * If balanced, clear the dirty and congested + * flags + */ + clear_bit(ZONE_CONGESTED, &zone->flags); + clear_bit(ZONE_DIRTY, &zone->flags); + } + } + + if (i < 0) + goto out; + + for (i = 0; i <= end_zone; i++) { + struct zone *zone = pgdat->node_zones + i; + + if (!populated_zone(zone)) + continue; + + /* + * If any zone is currently balanced then kswapd will + * not call compaction as it is expected that the + * necessary pages are already available. + */ + if (pgdat_needs_compaction && + zone_watermark_ok(zone, order, + low_wmark_pages(zone), + *classzone_idx, 0)) + pgdat_needs_compaction = false; + } + + /* + * If we're getting trouble reclaiming, start doing writepage + * even in laptop mode. + */ + if (sc.priority < DEF_PRIORITY - 2) + sc.may_writepage = 1; + + /* + * 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; + + if (!populated_zone(zone)) + continue; + + if (sc.priority != DEF_PRIORITY && + !zone_reclaimable(zone)) + 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; + + /* + * There should be no need to raise the scanning + * priority if enough pages are already being scanned + * that that high watermark would be met at 100% + * efficiency. + */ + if (kswapd_shrink_zone(zone, end_zone, + &sc, &nr_attempted)) + raise_priority = false; + } + + /* + * If the low watermark is met there is no need for processes + * to be throttled on pfmemalloc_wait as they should not be + * able to safely make forward progress. Wake them + */ + if (waitqueue_active(&pgdat->pfmemalloc_wait) && + pfmemalloc_watermark_ok(pgdat)) + wake_up_all(&pgdat->pfmemalloc_wait); + + /* + * Fragmentation may mean that the system cannot be rebalanced + * for high-order allocations in all zones. If twice the + * allocation size has been reclaimed and the zones are still + * not balanced then recheck the watermarks at order-0 to + * prevent kswapd reclaiming excessively. Assume that a + * process requested a high-order can direct reclaim/compact. + */ + if (order && sc.nr_reclaimed >= 2UL << order) + order = sc.order = 0; + + /* Check if kswapd should be suspending */ + if (try_to_freeze() || kthread_should_stop()) + break; + + /* + * Compact if necessary and kswapd is reclaiming at least the + * high watermark number of pages as requsted + */ + if (pgdat_needs_compaction && sc.nr_reclaimed > nr_attempted) + compact_pgdat(pgdat, order); + + /* + * Raise priority if scanning rate is too low or there was no + * progress in reclaiming pages + */ + if (raise_priority || !sc.nr_reclaimed) + sc.priority--; + } while (sc.priority >= 1 && + !pgdat_balanced(pgdat, order, *classzone_idx)); + +out: + /* + * Return the order we were reclaiming at so prepare_kswapd_sleep() + * 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 (prepare_kswapd_sleep(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 (prepare_kswapd_sleep(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); + + /* + * Compaction records what page blocks it recently failed to + * isolate pages from and skips them in the future scanning. + * When kswapd is going to sleep, it is reasonable to assume + * that pages and compaction may succeed so reset the cache. + */ + reset_isolation_suitable(pgdat); + + 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 ( ; ; ) { + bool 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); + } + } + + tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD); + current->reclaim_state = NULL; + lockdep_clear_current_reclaim_state(); + + 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; + +#ifdef CONFIG_FREEZER + if (pm_freezing) + return; +#endif + + if (!cpuset_zone_allowed(zone, GFP_KERNEL | __GFP_HARDWALL)) + 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_balanced(zone, order, 0, 0)) + return; + + trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order); + wake_up_interruptible(&pgdat->kswapd_wait); +} + +#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_memory_mask(unsigned long nr_to_reclaim, gfp_t mask) +{ + struct reclaim_state reclaim_state; + struct scan_control sc = { + .nr_to_reclaim = nr_to_reclaim, + .gfp_mask = GFP_HIGHUSER_MOVABLE, + .priority = DEF_PRIORITY, + .may_writepage = 1, + .may_unmap = 1, + .may_swap = 1, + .hibernation_mode = 1, + }; + 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); + + p->reclaim_state = NULL; + lockdep_clear_current_reclaim_state(); + p->flags &= ~PF_MEMALLOC; + + return nr_reclaimed; +} + +unsigned long shrink_all_memory(unsigned long nr_to_reclaim) +{ + return shrink_memory_mask(nr_to_reclaim, GFP_HIGHUSER_MOVABLE); +} +#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 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_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); + pr_err("Failed to start kswapd on node %d\n", nid); + ret = PTR_ERR(pgdat->kswapd); + pgdat->kswapd = NULL; + } + return ret; +} + +/* + * Called by memory hotplug when all memory in a node is offlined. Caller must + * hold mem_hotplug_begin/end(). + */ +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_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; + struct scan_control sc = { + .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), + .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)), + .order = order, + .priority = ZONE_RECLAIM_PRIORITY, + .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE), + .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP), + .may_swap = 1, + }; + + 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. + */ + do { + shrink_zone(zone, &sc, true); + } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0); + } + + 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_reclaimable(zone)) + 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 (test_and_set_bit(ZONE_RECLAIM_LOCKED, &zone->flags)) + return ZONE_RECLAIM_NOSCAN; + + ret = __zone_reclaim(zone, gfp_mask, order); + clear_bit(ZONE_RECLAIM_LOCKED, &zone->flags); + + 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 + * + * Test whether page is evictable--i.e., should be placed on active/inactive + * lists vs unevictable list. + * + * 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) +{ + return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page); +} + +#ifdef CONFIG_SHMEM +/** + * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list + * @pages: array of pages to check + * @nr_pages: number of pages to check + * + * Checks pages for evictability and moves them to the appropriate lru list. + * + * This function is only used for SysV IPC SHM_UNLOCK. + */ +void check_move_unevictable_pages(struct page **pages, int nr_pages) +{ + struct lruvec *lruvec; + struct zone *zone = NULL; + int pgscanned = 0; + int pgrescued = 0; + int i; + + for (i = 0; i < nr_pages; i++) { + struct page *page = pages[i]; + struct zone *pagezone; + + pgscanned++; + pagezone = page_zone(page); + if (pagezone != zone) { + if (zone) + spin_unlock_irq(&zone->lru_lock); + zone = pagezone; + spin_lock_irq(&zone->lru_lock); + } + lruvec = mem_cgroup_page_lruvec(page, zone); + + if (!PageLRU(page) || !PageUnevictable(page)) + continue; + + if (page_evictable(page)) { + enum lru_list lru = page_lru_base_type(page); + + VM_BUG_ON_PAGE(PageActive(page), page); + ClearPageUnevictable(page); + del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE); + add_page_to_lru_list(page, lruvec, lru); + pgrescued++; + } + } + + if (zone) { + __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued); + __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned); + spin_unlock_irq(&zone->lru_lock); + } +} +#endif /* CONFIG_SHMEM */ |