| // SPDX-License-Identifier: GPL-2.0 |
| /* |
| * Workingset detection |
| * |
| * Copyright (C) 2013 Red Hat, Inc., Johannes Weiner |
| */ |
| |
| #include <linux/memcontrol.h> |
| #include <linux/mm_inline.h> |
| #include <linux/writeback.h> |
| #include <linux/shmem_fs.h> |
| #include <linux/pagemap.h> |
| #include <linux/atomic.h> |
| #include <linux/module.h> |
| #include <linux/swap.h> |
| #include <linux/dax.h> |
| #include <linux/fs.h> |
| #include <linux/mm.h> |
| #include "internal.h" |
| |
| /* |
| * Double CLOCK lists |
| * |
| * Per node, two clock lists are maintained for file pages: the |
| * inactive and the active list. Freshly faulted pages start out at |
| * the head of the inactive list and page reclaim scans pages from the |
| * tail. Pages that are accessed multiple times on the inactive list |
| * are promoted to the active list, to protect them from reclaim, |
| * whereas active pages are demoted to the inactive list when the |
| * active list grows too big. |
| * |
| * fault ------------------------+ |
| * | |
| * +--------------+ | +-------------+ |
| * reclaim <- | inactive | <-+-- demotion | active | <--+ |
| * +--------------+ +-------------+ | |
| * | | |
| * +-------------- promotion ------------------+ |
| * |
| * |
| * Access frequency and refault distance |
| * |
| * A workload is thrashing when its pages are frequently used but they |
| * are evicted from the inactive list every time before another access |
| * would have promoted them to the active list. |
| * |
| * In cases where the average access distance between thrashing pages |
| * is bigger than the size of memory there is nothing that can be |
| * done - the thrashing set could never fit into memory under any |
| * circumstance. |
| * |
| * However, the average access distance could be bigger than the |
| * inactive list, yet smaller than the size of memory. In this case, |
| * the set could fit into memory if it weren't for the currently |
| * active pages - which may be used more, hopefully less frequently: |
| * |
| * +-memory available to cache-+ |
| * | | |
| * +-inactive------+-active----+ |
| * a b | c d e f g h i | J K L M N | |
| * +---------------+-----------+ |
| * |
| * It is prohibitively expensive to accurately track access frequency |
| * of pages. But a reasonable approximation can be made to measure |
| * thrashing on the inactive list, after which refaulting pages can be |
| * activated optimistically to compete with the existing active pages. |
| * |
| * Approximating inactive page access frequency - Observations: |
| * |
| * 1. When a page is accessed for the first time, it is added to the |
| * head of the inactive list, slides every existing inactive page |
| * towards the tail by one slot, and pushes the current tail page |
| * out of memory. |
| * |
| * 2. When a page is accessed for the second time, it is promoted to |
| * the active list, shrinking the inactive list by one slot. This |
| * also slides all inactive pages that were faulted into the cache |
| * more recently than the activated page towards the tail of the |
| * inactive list. |
| * |
| * Thus: |
| * |
| * 1. The sum of evictions and activations between any two points in |
| * time indicate the minimum number of inactive pages accessed in |
| * between. |
| * |
| * 2. Moving one inactive page N page slots towards the tail of the |
| * list requires at least N inactive page accesses. |
| * |
| * Combining these: |
| * |
| * 1. When a page is finally evicted from memory, the number of |
| * inactive pages accessed while the page was in cache is at least |
| * the number of page slots on the inactive list. |
| * |
| * 2. In addition, measuring the sum of evictions and activations (E) |
| * at the time of a page's eviction, and comparing it to another |
| * reading (R) at the time the page faults back into memory tells |
| * the minimum number of accesses while the page was not cached. |
| * This is called the refault distance. |
| * |
| * Because the first access of the page was the fault and the second |
| * access the refault, we combine the in-cache distance with the |
| * out-of-cache distance to get the complete minimum access distance |
| * of this page: |
| * |
| * NR_inactive + (R - E) |
| * |
| * And knowing the minimum access distance of a page, we can easily |
| * tell if the page would be able to stay in cache assuming all page |
| * slots in the cache were available: |
| * |
| * NR_inactive + (R - E) <= NR_inactive + NR_active |
| * |
| * If we have swap we should consider about NR_inactive_anon and |
| * NR_active_anon, so for page cache and anonymous respectively: |
| * |
| * NR_inactive_file + (R - E) <= NR_inactive_file + NR_active_file |
| * + NR_inactive_anon + NR_active_anon |
| * |
| * NR_inactive_anon + (R - E) <= NR_inactive_anon + NR_active_anon |
| * + NR_inactive_file + NR_active_file |
| * |
| * Which can be further simplified to: |
| * |
| * (R - E) <= NR_active_file + NR_inactive_anon + NR_active_anon |
| * |
| * (R - E) <= NR_active_anon + NR_inactive_file + NR_active_file |
| * |
| * Put into words, the refault distance (out-of-cache) can be seen as |
| * a deficit in inactive list space (in-cache). If the inactive list |
| * had (R - E) more page slots, the page would not have been evicted |
| * in between accesses, but activated instead. And on a full system, |
| * the only thing eating into inactive list space is active pages. |
| * |
| * |
| * Refaulting inactive pages |
| * |
| * All that is known about the active list is that the pages have been |
| * accessed more than once in the past. This means that at any given |
| * time there is actually a good chance that pages on the active list |
| * are no longer in active use. |
| * |
| * So when a refault distance of (R - E) is observed and there are at |
| * least (R - E) pages in the userspace workingset, the refaulting page |
| * is activated optimistically in the hope that (R - E) pages are actually |
| * used less frequently than the refaulting page - or even not used at |
| * all anymore. |
| * |
| * That means if inactive cache is refaulting with a suitable refault |
| * distance, we assume the cache workingset is transitioning and put |
| * pressure on the current workingset. |
| * |
| * If this is wrong and demotion kicks in, the pages which are truly |
| * used more frequently will be reactivated while the less frequently |
| * used once will be evicted from memory. |
| * |
| * But if this is right, the stale pages will be pushed out of memory |
| * and the used pages get to stay in cache. |
| * |
| * Refaulting active pages |
| * |
| * If on the other hand the refaulting pages have recently been |
| * deactivated, it means that the active list is no longer protecting |
| * actively used cache from reclaim. The cache is NOT transitioning to |
| * a different workingset; the existing workingset is thrashing in the |
| * space allocated to the page cache. |
| * |
| * |
| * Implementation |
| * |
| * For each node's LRU lists, a counter for inactive evictions and |
| * activations is maintained (node->nonresident_age). |
| * |
| * On eviction, a snapshot of this counter (along with some bits to |
| * identify the node) is stored in the now empty page cache |
| * slot of the evicted page. This is called a shadow entry. |
| * |
| * On cache misses for which there are shadow entries, an eligible |
| * refault distance will immediately activate the refaulting page. |
| */ |
| |
| #define WORKINGSET_SHIFT 1 |
| #define EVICTION_SHIFT ((BITS_PER_LONG - BITS_PER_XA_VALUE) + \ |
| WORKINGSET_SHIFT + NODES_SHIFT + \ |
| MEM_CGROUP_ID_SHIFT) |
| #define EVICTION_MASK (~0UL >> EVICTION_SHIFT) |
| |
| /* |
| * Eviction timestamps need to be able to cover the full range of |
| * actionable refaults. However, bits are tight in the xarray |
| * entry, and after storing the identifier for the lruvec there might |
| * not be enough left to represent every single actionable refault. In |
| * that case, we have to sacrifice granularity for distance, and group |
| * evictions into coarser buckets by shaving off lower timestamp bits. |
| */ |
| static unsigned int bucket_order __read_mostly; |
| |
| static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction, |
| bool workingset) |
| { |
| eviction &= EVICTION_MASK; |
| eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid; |
| eviction = (eviction << NODES_SHIFT) | pgdat->node_id; |
| eviction = (eviction << WORKINGSET_SHIFT) | workingset; |
| |
| return xa_mk_value(eviction); |
| } |
| |
| static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat, |
| unsigned long *evictionp, bool *workingsetp) |
| { |
| unsigned long entry = xa_to_value(shadow); |
| int memcgid, nid; |
| bool workingset; |
| |
| workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1); |
| entry >>= WORKINGSET_SHIFT; |
| nid = entry & ((1UL << NODES_SHIFT) - 1); |
| entry >>= NODES_SHIFT; |
| memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1); |
| entry >>= MEM_CGROUP_ID_SHIFT; |
| |
| *memcgidp = memcgid; |
| *pgdat = NODE_DATA(nid); |
| *evictionp = entry; |
| *workingsetp = workingset; |
| } |
| |
| #ifdef CONFIG_LRU_GEN |
| |
| static void *lru_gen_eviction(struct folio *folio) |
| { |
| int hist; |
| unsigned long token; |
| unsigned long min_seq; |
| struct lruvec *lruvec; |
| struct lru_gen_folio *lrugen; |
| int type = folio_is_file_lru(folio); |
| int delta = folio_nr_pages(folio); |
| int refs = folio_lru_refs(folio); |
| int tier = lru_tier_from_refs(refs); |
| struct mem_cgroup *memcg = folio_memcg(folio); |
| struct pglist_data *pgdat = folio_pgdat(folio); |
| |
| BUILD_BUG_ON(LRU_GEN_WIDTH + LRU_REFS_WIDTH > BITS_PER_LONG - EVICTION_SHIFT); |
| |
| lruvec = mem_cgroup_lruvec(memcg, pgdat); |
| lrugen = &lruvec->lrugen; |
| min_seq = READ_ONCE(lrugen->min_seq[type]); |
| token = (min_seq << LRU_REFS_WIDTH) | max(refs - 1, 0); |
| |
| hist = lru_hist_from_seq(min_seq); |
| atomic_long_add(delta, &lrugen->evicted[hist][type][tier]); |
| |
| return pack_shadow(mem_cgroup_id(memcg), pgdat, token, refs); |
| } |
| |
| /* |
| * Tests if the shadow entry is for a folio that was recently evicted. |
| * Fills in @lruvec, @token, @workingset with the values unpacked from shadow. |
| */ |
| static bool lru_gen_test_recent(void *shadow, bool file, struct lruvec **lruvec, |
| unsigned long *token, bool *workingset) |
| { |
| int memcg_id; |
| unsigned long min_seq; |
| struct mem_cgroup *memcg; |
| struct pglist_data *pgdat; |
| |
| unpack_shadow(shadow, &memcg_id, &pgdat, token, workingset); |
| |
| memcg = mem_cgroup_from_id(memcg_id); |
| *lruvec = mem_cgroup_lruvec(memcg, pgdat); |
| |
| min_seq = READ_ONCE((*lruvec)->lrugen.min_seq[file]); |
| return (*token >> LRU_REFS_WIDTH) == (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)); |
| } |
| |
| static void lru_gen_refault(struct folio *folio, void *shadow) |
| { |
| bool recent; |
| int hist, tier, refs; |
| bool workingset; |
| unsigned long token; |
| struct lruvec *lruvec; |
| struct lru_gen_folio *lrugen; |
| int type = folio_is_file_lru(folio); |
| int delta = folio_nr_pages(folio); |
| |
| rcu_read_lock(); |
| |
| recent = lru_gen_test_recent(shadow, type, &lruvec, &token, &workingset); |
| if (lruvec != folio_lruvec(folio)) |
| goto unlock; |
| |
| mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + type, delta); |
| |
| if (!recent) |
| goto unlock; |
| |
| lrugen = &lruvec->lrugen; |
| |
| hist = lru_hist_from_seq(READ_ONCE(lrugen->min_seq[type])); |
| /* see the comment in folio_lru_refs() */ |
| refs = (token & (BIT(LRU_REFS_WIDTH) - 1)) + workingset; |
| tier = lru_tier_from_refs(refs); |
| |
| atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]); |
| mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta); |
| |
| /* |
| * Count the following two cases as stalls: |
| * 1. For pages accessed through page tables, hotter pages pushed out |
| * hot pages which refaulted immediately. |
| * 2. For pages accessed multiple times through file descriptors, |
| * they would have been protected by sort_folio(). |
| */ |
| if (lru_gen_in_fault() || refs >= BIT(LRU_REFS_WIDTH) - 1) { |
| set_mask_bits(&folio->flags, 0, LRU_REFS_MASK | BIT(PG_workingset)); |
| mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta); |
| } |
| unlock: |
| rcu_read_unlock(); |
| } |
| |
| #else /* !CONFIG_LRU_GEN */ |
| |
| static void *lru_gen_eviction(struct folio *folio) |
| { |
| return NULL; |
| } |
| |
| static bool lru_gen_test_recent(void *shadow, bool file, struct lruvec **lruvec, |
| unsigned long *token, bool *workingset) |
| { |
| return false; |
| } |
| |
| static void lru_gen_refault(struct folio *folio, void *shadow) |
| { |
| } |
| |
| #endif /* CONFIG_LRU_GEN */ |
| |
| /** |
| * workingset_age_nonresident - age non-resident entries as LRU ages |
| * @lruvec: the lruvec that was aged |
| * @nr_pages: the number of pages to count |
| * |
| * As in-memory pages are aged, non-resident pages need to be aged as |
| * well, in order for the refault distances later on to be comparable |
| * to the in-memory dimensions. This function allows reclaim and LRU |
| * operations to drive the non-resident aging along in parallel. |
| */ |
| void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages) |
| { |
| /* |
| * Reclaiming a cgroup means reclaiming all its children in a |
| * round-robin fashion. That means that each cgroup has an LRU |
| * order that is composed of the LRU orders of its child |
| * cgroups; and every page has an LRU position not just in the |
| * cgroup that owns it, but in all of that group's ancestors. |
| * |
| * So when the physical inactive list of a leaf cgroup ages, |
| * the virtual inactive lists of all its parents, including |
| * the root cgroup's, age as well. |
| */ |
| do { |
| atomic_long_add(nr_pages, &lruvec->nonresident_age); |
| } while ((lruvec = parent_lruvec(lruvec))); |
| } |
| |
| /** |
| * workingset_eviction - note the eviction of a folio from memory |
| * @target_memcg: the cgroup that is causing the reclaim |
| * @folio: the folio being evicted |
| * |
| * Return: a shadow entry to be stored in @folio->mapping->i_pages in place |
| * of the evicted @folio so that a later refault can be detected. |
| */ |
| void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg) |
| { |
| struct pglist_data *pgdat = folio_pgdat(folio); |
| unsigned long eviction; |
| struct lruvec *lruvec; |
| int memcgid; |
| |
| /* Folio is fully exclusive and pins folio's memory cgroup pointer */ |
| VM_BUG_ON_FOLIO(folio_test_lru(folio), folio); |
| VM_BUG_ON_FOLIO(folio_ref_count(folio), folio); |
| VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); |
| |
| if (lru_gen_enabled()) |
| return lru_gen_eviction(folio); |
| |
| lruvec = mem_cgroup_lruvec(target_memcg, pgdat); |
| /* XXX: target_memcg can be NULL, go through lruvec */ |
| memcgid = mem_cgroup_id(lruvec_memcg(lruvec)); |
| eviction = atomic_long_read(&lruvec->nonresident_age); |
| eviction >>= bucket_order; |
| workingset_age_nonresident(lruvec, folio_nr_pages(folio)); |
| return pack_shadow(memcgid, pgdat, eviction, |
| folio_test_workingset(folio)); |
| } |
| |
| /** |
| * workingset_test_recent - tests if the shadow entry is for a folio that was |
| * recently evicted. Also fills in @workingset with the value unpacked from |
| * shadow. |
| * @shadow: the shadow entry to be tested. |
| * @file: whether the corresponding folio is from the file lru. |
| * @workingset: where the workingset value unpacked from shadow should |
| * be stored. |
| * |
| * Return: true if the shadow is for a recently evicted folio; false otherwise. |
| */ |
| bool workingset_test_recent(void *shadow, bool file, bool *workingset) |
| { |
| struct mem_cgroup *eviction_memcg; |
| struct lruvec *eviction_lruvec; |
| unsigned long refault_distance; |
| unsigned long workingset_size; |
| unsigned long refault; |
| int memcgid; |
| struct pglist_data *pgdat; |
| unsigned long eviction; |
| |
| rcu_read_lock(); |
| |
| if (lru_gen_enabled()) { |
| bool recent = lru_gen_test_recent(shadow, file, |
| &eviction_lruvec, &eviction, workingset); |
| |
| rcu_read_unlock(); |
| return recent; |
| } |
| |
| |
| unpack_shadow(shadow, &memcgid, &pgdat, &eviction, workingset); |
| eviction <<= bucket_order; |
| |
| /* |
| * Look up the memcg associated with the stored ID. It might |
| * have been deleted since the folio's eviction. |
| * |
| * Note that in rare events the ID could have been recycled |
| * for a new cgroup that refaults a shared folio. This is |
| * impossible to tell from the available data. However, this |
| * should be a rare and limited disturbance, and activations |
| * are always speculative anyway. Ultimately, it's the aging |
| * algorithm's job to shake out the minimum access frequency |
| * for the active cache. |
| * |
| * XXX: On !CONFIG_MEMCG, this will always return NULL; it |
| * would be better if the root_mem_cgroup existed in all |
| * configurations instead. |
| */ |
| eviction_memcg = mem_cgroup_from_id(memcgid); |
| if (!mem_cgroup_disabled() && |
| (!eviction_memcg || !mem_cgroup_tryget(eviction_memcg))) { |
| rcu_read_unlock(); |
| return false; |
| } |
| |
| rcu_read_unlock(); |
| |
| /* |
| * Flush stats (and potentially sleep) outside the RCU read section. |
| * XXX: With per-memcg flushing and thresholding, is ratelimiting |
| * still needed here? |
| */ |
| mem_cgroup_flush_stats_ratelimited(eviction_memcg); |
| |
| eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat); |
| refault = atomic_long_read(&eviction_lruvec->nonresident_age); |
| |
| /* |
| * Calculate the refault distance |
| * |
| * The unsigned subtraction here gives an accurate distance |
| * across nonresident_age overflows in most cases. There is a |
| * special case: usually, shadow entries have a short lifetime |
| * and are either refaulted or reclaimed along with the inode |
| * before they get too old. But it is not impossible for the |
| * nonresident_age to lap a shadow entry in the field, which |
| * can then result in a false small refault distance, leading |
| * to a false activation should this old entry actually |
| * refault again. However, earlier kernels used to deactivate |
| * unconditionally with *every* reclaim invocation for the |
| * longest time, so the occasional inappropriate activation |
| * leading to pressure on the active list is not a problem. |
| */ |
| refault_distance = (refault - eviction) & EVICTION_MASK; |
| |
| /* |
| * Compare the distance to the existing workingset size. We |
| * don't activate pages that couldn't stay resident even if |
| * all the memory was available to the workingset. Whether |
| * workingset competition needs to consider anon or not depends |
| * on having free swap space. |
| */ |
| workingset_size = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE); |
| if (!file) { |
| workingset_size += lruvec_page_state(eviction_lruvec, |
| NR_INACTIVE_FILE); |
| } |
| if (mem_cgroup_get_nr_swap_pages(eviction_memcg) > 0) { |
| workingset_size += lruvec_page_state(eviction_lruvec, |
| NR_ACTIVE_ANON); |
| if (file) { |
| workingset_size += lruvec_page_state(eviction_lruvec, |
| NR_INACTIVE_ANON); |
| } |
| } |
| |
| mem_cgroup_put(eviction_memcg); |
| return refault_distance <= workingset_size; |
| } |
| |
| /** |
| * workingset_refault - Evaluate the refault of a previously evicted folio. |
| * @folio: The freshly allocated replacement folio. |
| * @shadow: Shadow entry of the evicted folio. |
| * |
| * Calculates and evaluates the refault distance of the previously |
| * evicted folio in the context of the node and the memcg whose memory |
| * pressure caused the eviction. |
| */ |
| void workingset_refault(struct folio *folio, void *shadow) |
| { |
| bool file = folio_is_file_lru(folio); |
| struct pglist_data *pgdat; |
| struct mem_cgroup *memcg; |
| struct lruvec *lruvec; |
| bool workingset; |
| long nr; |
| |
| if (lru_gen_enabled()) { |
| lru_gen_refault(folio, shadow); |
| return; |
| } |
| |
| /* |
| * The activation decision for this folio is made at the level |
| * where the eviction occurred, as that is where the LRU order |
| * during folio reclaim is being determined. |
| * |
| * However, the cgroup that will own the folio is the one that |
| * is actually experiencing the refault event. Make sure the folio is |
| * locked to guarantee folio_memcg() stability throughout. |
| */ |
| VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); |
| nr = folio_nr_pages(folio); |
| memcg = folio_memcg(folio); |
| pgdat = folio_pgdat(folio); |
| lruvec = mem_cgroup_lruvec(memcg, pgdat); |
| |
| mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr); |
| |
| if (!workingset_test_recent(shadow, file, &workingset)) |
| return; |
| |
| folio_set_active(folio); |
| workingset_age_nonresident(lruvec, nr); |
| mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file, nr); |
| |
| /* Folio was active prior to eviction */ |
| if (workingset) { |
| folio_set_workingset(folio); |
| /* |
| * XXX: Move to folio_add_lru() when it supports new vs |
| * putback |
| */ |
| lru_note_cost_refault(folio); |
| mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr); |
| } |
| } |
| |
| /** |
| * workingset_activation - note a page activation |
| * @folio: Folio that is being activated. |
| */ |
| void workingset_activation(struct folio *folio) |
| { |
| struct mem_cgroup *memcg; |
| |
| rcu_read_lock(); |
| /* |
| * Filter non-memcg pages here, e.g. unmap can call |
| * mark_page_accessed() on VDSO pages. |
| * |
| * XXX: See workingset_refault() - this should return |
| * root_mem_cgroup even for !CONFIG_MEMCG. |
| */ |
| memcg = folio_memcg_rcu(folio); |
| if (!mem_cgroup_disabled() && !memcg) |
| goto out; |
| workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio)); |
| out: |
| rcu_read_unlock(); |
| } |
| |
| /* |
| * Shadow entries reflect the share of the working set that does not |
| * fit into memory, so their number depends on the access pattern of |
| * the workload. In most cases, they will refault or get reclaimed |
| * along with the inode, but a (malicious) workload that streams |
| * through files with a total size several times that of available |
| * memory, while preventing the inodes from being reclaimed, can |
| * create excessive amounts of shadow nodes. To keep a lid on this, |
| * track shadow nodes and reclaim them when they grow way past the |
| * point where they would still be useful. |
| */ |
| |
| struct list_lru shadow_nodes; |
| |
| void workingset_update_node(struct xa_node *node) |
| { |
| struct address_space *mapping; |
| struct page *page = virt_to_page(node); |
| |
| /* |
| * Track non-empty nodes that contain only shadow entries; |
| * unlink those that contain pages or are being freed. |
| * |
| * Avoid acquiring the list_lru lock when the nodes are |
| * already where they should be. The list_empty() test is safe |
| * as node->private_list is protected by the i_pages lock. |
| */ |
| mapping = container_of(node->array, struct address_space, i_pages); |
| lockdep_assert_held(&mapping->i_pages.xa_lock); |
| |
| if (node->count && node->count == node->nr_values) { |
| if (list_empty(&node->private_list)) { |
| list_lru_add_obj(&shadow_nodes, &node->private_list); |
| __inc_node_page_state(page, WORKINGSET_NODES); |
| } |
| } else { |
| if (!list_empty(&node->private_list)) { |
| list_lru_del_obj(&shadow_nodes, &node->private_list); |
| __dec_node_page_state(page, WORKINGSET_NODES); |
| } |
| } |
| } |
| |
| static unsigned long count_shadow_nodes(struct shrinker *shrinker, |
| struct shrink_control *sc) |
| { |
| unsigned long max_nodes; |
| unsigned long nodes; |
| unsigned long pages; |
| |
| nodes = list_lru_shrink_count(&shadow_nodes, sc); |
| if (!nodes) |
| return SHRINK_EMPTY; |
| |
| /* |
| * Approximate a reasonable limit for the nodes |
| * containing shadow entries. We don't need to keep more |
| * shadow entries than possible pages on the active list, |
| * since refault distances bigger than that are dismissed. |
| * |
| * The size of the active list converges toward 100% of |
| * overall page cache as memory grows, with only a tiny |
| * inactive list. Assume the total cache size for that. |
| * |
| * Nodes might be sparsely populated, with only one shadow |
| * entry in the extreme case. Obviously, we cannot keep one |
| * node for every eligible shadow entry, so compromise on a |
| * worst-case density of 1/8th. Below that, not all eligible |
| * refaults can be detected anymore. |
| * |
| * On 64-bit with 7 xa_nodes per page and 64 slots |
| * each, this will reclaim shadow entries when they consume |
| * ~1.8% of available memory: |
| * |
| * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE |
| */ |
| #ifdef CONFIG_MEMCG |
| if (sc->memcg) { |
| struct lruvec *lruvec; |
| int i; |
| |
| mem_cgroup_flush_stats_ratelimited(sc->memcg); |
| lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid)); |
| for (pages = 0, i = 0; i < NR_LRU_LISTS; i++) |
| pages += lruvec_page_state_local(lruvec, |
| NR_LRU_BASE + i); |
| pages += lruvec_page_state_local( |
| lruvec, NR_SLAB_RECLAIMABLE_B) >> PAGE_SHIFT; |
| pages += lruvec_page_state_local( |
| lruvec, NR_SLAB_UNRECLAIMABLE_B) >> PAGE_SHIFT; |
| } else |
| #endif |
| pages = node_present_pages(sc->nid); |
| |
| max_nodes = pages >> (XA_CHUNK_SHIFT - 3); |
| |
| if (nodes <= max_nodes) |
| return 0; |
| return nodes - max_nodes; |
| } |
| |
| static enum lru_status shadow_lru_isolate(struct list_head *item, |
| struct list_lru_one *lru, |
| spinlock_t *lru_lock, |
| void *arg) __must_hold(lru_lock) |
| { |
| struct xa_node *node = container_of(item, struct xa_node, private_list); |
| struct address_space *mapping; |
| int ret; |
| |
| /* |
| * Page cache insertions and deletions synchronously maintain |
| * the shadow node LRU under the i_pages lock and the |
| * lru_lock. Because the page cache tree is emptied before |
| * the inode can be destroyed, holding the lru_lock pins any |
| * address_space that has nodes on the LRU. |
| * |
| * We can then safely transition to the i_pages lock to |
| * pin only the address_space of the particular node we want |
| * to reclaim, take the node off-LRU, and drop the lru_lock. |
| */ |
| |
| mapping = container_of(node->array, struct address_space, i_pages); |
| |
| /* Coming from the list, invert the lock order */ |
| if (!xa_trylock(&mapping->i_pages)) { |
| spin_unlock_irq(lru_lock); |
| ret = LRU_RETRY; |
| goto out; |
| } |
| |
| /* For page cache we need to hold i_lock */ |
| if (mapping->host != NULL) { |
| if (!spin_trylock(&mapping->host->i_lock)) { |
| xa_unlock(&mapping->i_pages); |
| spin_unlock_irq(lru_lock); |
| ret = LRU_RETRY; |
| goto out; |
| } |
| } |
| |
| list_lru_isolate(lru, item); |
| __dec_node_page_state(virt_to_page(node), WORKINGSET_NODES); |
| |
| spin_unlock(lru_lock); |
| |
| /* |
| * The nodes should only contain one or more shadow entries, |
| * no pages, so we expect to be able to remove them all and |
| * delete and free the empty node afterwards. |
| */ |
| if (WARN_ON_ONCE(!node->nr_values)) |
| goto out_invalid; |
| if (WARN_ON_ONCE(node->count != node->nr_values)) |
| goto out_invalid; |
| xa_delete_node(node, workingset_update_node); |
| __inc_lruvec_kmem_state(node, WORKINGSET_NODERECLAIM); |
| |
| out_invalid: |
| xa_unlock_irq(&mapping->i_pages); |
| if (mapping->host != NULL) { |
| if (mapping_shrinkable(mapping)) |
| inode_add_lru(mapping->host); |
| spin_unlock(&mapping->host->i_lock); |
| } |
| ret = LRU_REMOVED_RETRY; |
| out: |
| cond_resched(); |
| spin_lock_irq(lru_lock); |
| return ret; |
| } |
| |
| static unsigned long scan_shadow_nodes(struct shrinker *shrinker, |
| struct shrink_control *sc) |
| { |
| /* list_lru lock nests inside the IRQ-safe i_pages lock */ |
| return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate, |
| NULL); |
| } |
| |
| /* |
| * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe |
| * i_pages lock. |
| */ |
| static struct lock_class_key shadow_nodes_key; |
| |
| static int __init workingset_init(void) |
| { |
| struct shrinker *workingset_shadow_shrinker; |
| unsigned int timestamp_bits; |
| unsigned int max_order; |
| int ret = -ENOMEM; |
| |
| BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT); |
| /* |
| * Calculate the eviction bucket size to cover the longest |
| * actionable refault distance, which is currently half of |
| * memory (totalram_pages/2). However, memory hotplug may add |
| * some more pages at runtime, so keep working with up to |
| * double the initial memory by using totalram_pages as-is. |
| */ |
| timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT; |
| max_order = fls_long(totalram_pages() - 1); |
| if (max_order > timestamp_bits) |
| bucket_order = max_order - timestamp_bits; |
| pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n", |
| timestamp_bits, max_order, bucket_order); |
| |
| workingset_shadow_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE | |
| SHRINKER_MEMCG_AWARE, |
| "mm-shadow"); |
| if (!workingset_shadow_shrinker) |
| goto err; |
| |
| ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key, |
| workingset_shadow_shrinker); |
| if (ret) |
| goto err_list_lru; |
| |
| workingset_shadow_shrinker->count_objects = count_shadow_nodes; |
| workingset_shadow_shrinker->scan_objects = scan_shadow_nodes; |
| /* ->count reports only fully expendable nodes */ |
| workingset_shadow_shrinker->seeks = 0; |
| |
| shrinker_register(workingset_shadow_shrinker); |
| return 0; |
| err_list_lru: |
| shrinker_free(workingset_shadow_shrinker); |
| err: |
| return ret; |
| } |
| module_init(workingset_init); |