LCOV - code coverage report
Current view: top level - mm - workingset.c (source / functions) Hit Total Coverage
Test: coverage.info Lines: 11 113 9.7 %
Date: 2023-03-27 20:00:47 Functions: 1 10 10.0 %

          Line data    Source code
       1             : // SPDX-License-Identifier: GPL-2.0
       2             : /*
       3             :  * Workingset detection
       4             :  *
       5             :  * Copyright (C) 2013 Red Hat, Inc., Johannes Weiner
       6             :  */
       7             : 
       8             : #include <linux/memcontrol.h>
       9             : #include <linux/mm_inline.h>
      10             : #include <linux/writeback.h>
      11             : #include <linux/shmem_fs.h>
      12             : #include <linux/pagemap.h>
      13             : #include <linux/atomic.h>
      14             : #include <linux/module.h>
      15             : #include <linux/swap.h>
      16             : #include <linux/dax.h>
      17             : #include <linux/fs.h>
      18             : #include <linux/mm.h>
      19             : 
      20             : /*
      21             :  *              Double CLOCK lists
      22             :  *
      23             :  * Per node, two clock lists are maintained for file pages: the
      24             :  * inactive and the active list.  Freshly faulted pages start out at
      25             :  * the head of the inactive list and page reclaim scans pages from the
      26             :  * tail.  Pages that are accessed multiple times on the inactive list
      27             :  * are promoted to the active list, to protect them from reclaim,
      28             :  * whereas active pages are demoted to the inactive list when the
      29             :  * active list grows too big.
      30             :  *
      31             :  *   fault ------------------------+
      32             :  *                                 |
      33             :  *              +--------------+   |            +-------------+
      34             :  *   reclaim <- |   inactive   | <-+-- demotion |    active   | <--+
      35             :  *              +--------------+                +-------------+    |
      36             :  *                     |                                           |
      37             :  *                     +-------------- promotion ------------------+
      38             :  *
      39             :  *
      40             :  *              Access frequency and refault distance
      41             :  *
      42             :  * A workload is thrashing when its pages are frequently used but they
      43             :  * are evicted from the inactive list every time before another access
      44             :  * would have promoted them to the active list.
      45             :  *
      46             :  * In cases where the average access distance between thrashing pages
      47             :  * is bigger than the size of memory there is nothing that can be
      48             :  * done - the thrashing set could never fit into memory under any
      49             :  * circumstance.
      50             :  *
      51             :  * However, the average access distance could be bigger than the
      52             :  * inactive list, yet smaller than the size of memory.  In this case,
      53             :  * the set could fit into memory if it weren't for the currently
      54             :  * active pages - which may be used more, hopefully less frequently:
      55             :  *
      56             :  *      +-memory available to cache-+
      57             :  *      |                           |
      58             :  *      +-inactive------+-active----+
      59             :  *  a b | c d e f g h i | J K L M N |
      60             :  *      +---------------+-----------+
      61             :  *
      62             :  * It is prohibitively expensive to accurately track access frequency
      63             :  * of pages.  But a reasonable approximation can be made to measure
      64             :  * thrashing on the inactive list, after which refaulting pages can be
      65             :  * activated optimistically to compete with the existing active pages.
      66             :  *
      67             :  * Approximating inactive page access frequency - Observations:
      68             :  *
      69             :  * 1. When a page is accessed for the first time, it is added to the
      70             :  *    head of the inactive list, slides every existing inactive page
      71             :  *    towards the tail by one slot, and pushes the current tail page
      72             :  *    out of memory.
      73             :  *
      74             :  * 2. When a page is accessed for the second time, it is promoted to
      75             :  *    the active list, shrinking the inactive list by one slot.  This
      76             :  *    also slides all inactive pages that were faulted into the cache
      77             :  *    more recently than the activated page towards the tail of the
      78             :  *    inactive list.
      79             :  *
      80             :  * Thus:
      81             :  *
      82             :  * 1. The sum of evictions and activations between any two points in
      83             :  *    time indicate the minimum number of inactive pages accessed in
      84             :  *    between.
      85             :  *
      86             :  * 2. Moving one inactive page N page slots towards the tail of the
      87             :  *    list requires at least N inactive page accesses.
      88             :  *
      89             :  * Combining these:
      90             :  *
      91             :  * 1. When a page is finally evicted from memory, the number of
      92             :  *    inactive pages accessed while the page was in cache is at least
      93             :  *    the number of page slots on the inactive list.
      94             :  *
      95             :  * 2. In addition, measuring the sum of evictions and activations (E)
      96             :  *    at the time of a page's eviction, and comparing it to another
      97             :  *    reading (R) at the time the page faults back into memory tells
      98             :  *    the minimum number of accesses while the page was not cached.
      99             :  *    This is called the refault distance.
     100             :  *
     101             :  * Because the first access of the page was the fault and the second
     102             :  * access the refault, we combine the in-cache distance with the
     103             :  * out-of-cache distance to get the complete minimum access distance
     104             :  * of this page:
     105             :  *
     106             :  *      NR_inactive + (R - E)
     107             :  *
     108             :  * And knowing the minimum access distance of a page, we can easily
     109             :  * tell if the page would be able to stay in cache assuming all page
     110             :  * slots in the cache were available:
     111             :  *
     112             :  *   NR_inactive + (R - E) <= NR_inactive + NR_active
     113             :  *
     114             :  * which can be further simplified to
     115             :  *
     116             :  *   (R - E) <= NR_active
     117             :  *
     118             :  * Put into words, the refault distance (out-of-cache) can be seen as
     119             :  * a deficit in inactive list space (in-cache).  If the inactive list
     120             :  * had (R - E) more page slots, the page would not have been evicted
     121             :  * in between accesses, but activated instead.  And on a full system,
     122             :  * the only thing eating into inactive list space is active pages.
     123             :  *
     124             :  *
     125             :  *              Refaulting inactive pages
     126             :  *
     127             :  * All that is known about the active list is that the pages have been
     128             :  * accessed more than once in the past.  This means that at any given
     129             :  * time there is actually a good chance that pages on the active list
     130             :  * are no longer in active use.
     131             :  *
     132             :  * So when a refault distance of (R - E) is observed and there are at
     133             :  * least (R - E) active pages, the refaulting page is activated
     134             :  * optimistically in the hope that (R - E) active pages are actually
     135             :  * used less frequently than the refaulting page - or even not used at
     136             :  * all anymore.
     137             :  *
     138             :  * That means if inactive cache is refaulting with a suitable refault
     139             :  * distance, we assume the cache workingset is transitioning and put
     140             :  * pressure on the current active list.
     141             :  *
     142             :  * If this is wrong and demotion kicks in, the pages which are truly
     143             :  * used more frequently will be reactivated while the less frequently
     144             :  * used once will be evicted from memory.
     145             :  *
     146             :  * But if this is right, the stale pages will be pushed out of memory
     147             :  * and the used pages get to stay in cache.
     148             :  *
     149             :  *              Refaulting active pages
     150             :  *
     151             :  * If on the other hand the refaulting pages have recently been
     152             :  * deactivated, it means that the active list is no longer protecting
     153             :  * actively used cache from reclaim. The cache is NOT transitioning to
     154             :  * a different workingset; the existing workingset is thrashing in the
     155             :  * space allocated to the page cache.
     156             :  *
     157             :  *
     158             :  *              Implementation
     159             :  *
     160             :  * For each node's LRU lists, a counter for inactive evictions and
     161             :  * activations is maintained (node->nonresident_age).
     162             :  *
     163             :  * On eviction, a snapshot of this counter (along with some bits to
     164             :  * identify the node) is stored in the now empty page cache
     165             :  * slot of the evicted page.  This is called a shadow entry.
     166             :  *
     167             :  * On cache misses for which there are shadow entries, an eligible
     168             :  * refault distance will immediately activate the refaulting page.
     169             :  */
     170             : 
     171             : #define WORKINGSET_SHIFT 1
     172             : #define EVICTION_SHIFT  ((BITS_PER_LONG - BITS_PER_XA_VALUE) +  \
     173             :                          WORKINGSET_SHIFT + NODES_SHIFT + \
     174             :                          MEM_CGROUP_ID_SHIFT)
     175             : #define EVICTION_MASK   (~0UL >> EVICTION_SHIFT)
     176             : 
     177             : /*
     178             :  * Eviction timestamps need to be able to cover the full range of
     179             :  * actionable refaults. However, bits are tight in the xarray
     180             :  * entry, and after storing the identifier for the lruvec there might
     181             :  * not be enough left to represent every single actionable refault. In
     182             :  * that case, we have to sacrifice granularity for distance, and group
     183             :  * evictions into coarser buckets by shaving off lower timestamp bits.
     184             :  */
     185             : static unsigned int bucket_order __read_mostly;
     186             : 
     187           0 : static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
     188             :                          bool workingset)
     189             : {
     190           0 :         eviction &= EVICTION_MASK;
     191           0 :         eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
     192           0 :         eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
     193           0 :         eviction = (eviction << WORKINGSET_SHIFT) | workingset;
     194             : 
     195           0 :         return xa_mk_value(eviction);
     196             : }
     197             : 
     198             : static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
     199             :                           unsigned long *evictionp, bool *workingsetp)
     200             : {
     201           0 :         unsigned long entry = xa_to_value(shadow);
     202             :         int memcgid, nid;
     203             :         bool workingset;
     204             : 
     205           0 :         workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1);
     206           0 :         entry >>= WORKINGSET_SHIFT;
     207           0 :         nid = entry & ((1UL << NODES_SHIFT) - 1);
     208           0 :         entry >>= NODES_SHIFT;
     209           0 :         memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
     210           0 :         entry >>= MEM_CGROUP_ID_SHIFT;
     211             : 
     212           0 :         *memcgidp = memcgid;
     213           0 :         *pgdat = NODE_DATA(nid);
     214           0 :         *evictionp = entry;
     215           0 :         *workingsetp = workingset;
     216             : }
     217             : 
     218             : #ifdef CONFIG_LRU_GEN
     219             : 
     220             : static void *lru_gen_eviction(struct folio *folio)
     221             : {
     222             :         int hist;
     223             :         unsigned long token;
     224             :         unsigned long min_seq;
     225             :         struct lruvec *lruvec;
     226             :         struct lru_gen_folio *lrugen;
     227             :         int type = folio_is_file_lru(folio);
     228             :         int delta = folio_nr_pages(folio);
     229             :         int refs = folio_lru_refs(folio);
     230             :         int tier = lru_tier_from_refs(refs);
     231             :         struct mem_cgroup *memcg = folio_memcg(folio);
     232             :         struct pglist_data *pgdat = folio_pgdat(folio);
     233             : 
     234             :         BUILD_BUG_ON(LRU_GEN_WIDTH + LRU_REFS_WIDTH > BITS_PER_LONG - EVICTION_SHIFT);
     235             : 
     236             :         lruvec = mem_cgroup_lruvec(memcg, pgdat);
     237             :         lrugen = &lruvec->lrugen;
     238             :         min_seq = READ_ONCE(lrugen->min_seq[type]);
     239             :         token = (min_seq << LRU_REFS_WIDTH) | max(refs - 1, 0);
     240             : 
     241             :         hist = lru_hist_from_seq(min_seq);
     242             :         atomic_long_add(delta, &lrugen->evicted[hist][type][tier]);
     243             : 
     244             :         return pack_shadow(mem_cgroup_id(memcg), pgdat, token, refs);
     245             : }
     246             : 
     247             : static void lru_gen_refault(struct folio *folio, void *shadow)
     248             : {
     249             :         int hist, tier, refs;
     250             :         int memcg_id;
     251             :         bool workingset;
     252             :         unsigned long token;
     253             :         unsigned long min_seq;
     254             :         struct lruvec *lruvec;
     255             :         struct lru_gen_folio *lrugen;
     256             :         struct mem_cgroup *memcg;
     257             :         struct pglist_data *pgdat;
     258             :         int type = folio_is_file_lru(folio);
     259             :         int delta = folio_nr_pages(folio);
     260             : 
     261             :         unpack_shadow(shadow, &memcg_id, &pgdat, &token, &workingset);
     262             : 
     263             :         if (pgdat != folio_pgdat(folio))
     264             :                 return;
     265             : 
     266             :         rcu_read_lock();
     267             : 
     268             :         memcg = folio_memcg_rcu(folio);
     269             :         if (memcg_id != mem_cgroup_id(memcg))
     270             :                 goto unlock;
     271             : 
     272             :         lruvec = mem_cgroup_lruvec(memcg, pgdat);
     273             :         lrugen = &lruvec->lrugen;
     274             : 
     275             :         min_seq = READ_ONCE(lrugen->min_seq[type]);
     276             :         if ((token >> LRU_REFS_WIDTH) != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)))
     277             :                 goto unlock;
     278             : 
     279             :         hist = lru_hist_from_seq(min_seq);
     280             :         /* see the comment in folio_lru_refs() */
     281             :         refs = (token & (BIT(LRU_REFS_WIDTH) - 1)) + workingset;
     282             :         tier = lru_tier_from_refs(refs);
     283             : 
     284             :         atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]);
     285             :         mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + type, delta);
     286             : 
     287             :         /*
     288             :          * Count the following two cases as stalls:
     289             :          * 1. For pages accessed through page tables, hotter pages pushed out
     290             :          *    hot pages which refaulted immediately.
     291             :          * 2. For pages accessed multiple times through file descriptors,
     292             :          *    numbers of accesses might have been out of the range.
     293             :          */
     294             :         if (lru_gen_in_fault() || refs == BIT(LRU_REFS_WIDTH)) {
     295             :                 folio_set_workingset(folio);
     296             :                 mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta);
     297             :         }
     298             : unlock:
     299             :         rcu_read_unlock();
     300             : }
     301             : 
     302             : #else /* !CONFIG_LRU_GEN */
     303             : 
     304             : static void *lru_gen_eviction(struct folio *folio)
     305             : {
     306             :         return NULL;
     307             : }
     308             : 
     309             : static void lru_gen_refault(struct folio *folio, void *shadow)
     310             : {
     311             : }
     312             : 
     313             : #endif /* CONFIG_LRU_GEN */
     314             : 
     315             : /**
     316             :  * workingset_age_nonresident - age non-resident entries as LRU ages
     317             :  * @lruvec: the lruvec that was aged
     318             :  * @nr_pages: the number of pages to count
     319             :  *
     320             :  * As in-memory pages are aged, non-resident pages need to be aged as
     321             :  * well, in order for the refault distances later on to be comparable
     322             :  * to the in-memory dimensions. This function allows reclaim and LRU
     323             :  * operations to drive the non-resident aging along in parallel.
     324             :  */
     325           0 : void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages)
     326             : {
     327             :         /*
     328             :          * Reclaiming a cgroup means reclaiming all its children in a
     329             :          * round-robin fashion. That means that each cgroup has an LRU
     330             :          * order that is composed of the LRU orders of its child
     331             :          * cgroups; and every page has an LRU position not just in the
     332             :          * cgroup that owns it, but in all of that group's ancestors.
     333             :          *
     334             :          * So when the physical inactive list of a leaf cgroup ages,
     335             :          * the virtual inactive lists of all its parents, including
     336             :          * the root cgroup's, age as well.
     337             :          */
     338             :         do {
     339           0 :                 atomic_long_add(nr_pages, &lruvec->nonresident_age);
     340           0 :         } while ((lruvec = parent_lruvec(lruvec)));
     341           0 : }
     342             : 
     343             : /**
     344             :  * workingset_eviction - note the eviction of a folio from memory
     345             :  * @target_memcg: the cgroup that is causing the reclaim
     346             :  * @folio: the folio being evicted
     347             :  *
     348             :  * Return: a shadow entry to be stored in @folio->mapping->i_pages in place
     349             :  * of the evicted @folio so that a later refault can be detected.
     350             :  */
     351           0 : void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
     352             : {
     353           0 :         struct pglist_data *pgdat = folio_pgdat(folio);
     354             :         unsigned long eviction;
     355             :         struct lruvec *lruvec;
     356             :         int memcgid;
     357             : 
     358             :         /* Folio is fully exclusive and pins folio's memory cgroup pointer */
     359             :         VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
     360             :         VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
     361             :         VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
     362             : 
     363             :         if (lru_gen_enabled())
     364             :                 return lru_gen_eviction(folio);
     365             : 
     366           0 :         lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
     367             :         /* XXX: target_memcg can be NULL, go through lruvec */
     368           0 :         memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
     369           0 :         eviction = atomic_long_read(&lruvec->nonresident_age);
     370           0 :         eviction >>= bucket_order;
     371           0 :         workingset_age_nonresident(lruvec, folio_nr_pages(folio));
     372           0 :         return pack_shadow(memcgid, pgdat, eviction,
     373           0 :                                 folio_test_workingset(folio));
     374             : }
     375             : 
     376             : /**
     377             :  * workingset_refault - Evaluate the refault of a previously evicted folio.
     378             :  * @folio: The freshly allocated replacement folio.
     379             :  * @shadow: Shadow entry of the evicted folio.
     380             :  *
     381             :  * Calculates and evaluates the refault distance of the previously
     382             :  * evicted folio in the context of the node and the memcg whose memory
     383             :  * pressure caused the eviction.
     384             :  */
     385           0 : void workingset_refault(struct folio *folio, void *shadow)
     386             : {
     387           0 :         bool file = folio_is_file_lru(folio);
     388             :         struct mem_cgroup *eviction_memcg;
     389             :         struct lruvec *eviction_lruvec;
     390             :         unsigned long refault_distance;
     391             :         unsigned long workingset_size;
     392             :         struct pglist_data *pgdat;
     393             :         struct mem_cgroup *memcg;
     394             :         unsigned long eviction;
     395             :         struct lruvec *lruvec;
     396             :         unsigned long refault;
     397             :         bool workingset;
     398             :         int memcgid;
     399             :         long nr;
     400             : 
     401             :         if (lru_gen_enabled()) {
     402             :                 lru_gen_refault(folio, shadow);
     403             :                 return;
     404             :         }
     405             : 
     406           0 :         unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
     407           0 :         eviction <<= bucket_order;
     408             : 
     409             :         rcu_read_lock();
     410             :         /*
     411             :          * Look up the memcg associated with the stored ID. It might
     412             :          * have been deleted since the folio's eviction.
     413             :          *
     414             :          * Note that in rare events the ID could have been recycled
     415             :          * for a new cgroup that refaults a shared folio. This is
     416             :          * impossible to tell from the available data. However, this
     417             :          * should be a rare and limited disturbance, and activations
     418             :          * are always speculative anyway. Ultimately, it's the aging
     419             :          * algorithm's job to shake out the minimum access frequency
     420             :          * for the active cache.
     421             :          *
     422             :          * XXX: On !CONFIG_MEMCG, this will always return NULL; it
     423             :          * would be better if the root_mem_cgroup existed in all
     424             :          * configurations instead.
     425             :          */
     426           0 :         eviction_memcg = mem_cgroup_from_id(memcgid);
     427             :         if (!mem_cgroup_disabled() && !eviction_memcg)
     428             :                 goto out;
     429           0 :         eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
     430           0 :         refault = atomic_long_read(&eviction_lruvec->nonresident_age);
     431             : 
     432             :         /*
     433             :          * Calculate the refault distance
     434             :          *
     435             :          * The unsigned subtraction here gives an accurate distance
     436             :          * across nonresident_age overflows in most cases. There is a
     437             :          * special case: usually, shadow entries have a short lifetime
     438             :          * and are either refaulted or reclaimed along with the inode
     439             :          * before they get too old.  But it is not impossible for the
     440             :          * nonresident_age to lap a shadow entry in the field, which
     441             :          * can then result in a false small refault distance, leading
     442             :          * to a false activation should this old entry actually
     443             :          * refault again.  However, earlier kernels used to deactivate
     444             :          * unconditionally with *every* reclaim invocation for the
     445             :          * longest time, so the occasional inappropriate activation
     446             :          * leading to pressure on the active list is not a problem.
     447             :          */
     448           0 :         refault_distance = (refault - eviction) & EVICTION_MASK;
     449             : 
     450             :         /*
     451             :          * The activation decision for this folio is made at the level
     452             :          * where the eviction occurred, as that is where the LRU order
     453             :          * during folio reclaim is being determined.
     454             :          *
     455             :          * However, the cgroup that will own the folio is the one that
     456             :          * is actually experiencing the refault event.
     457             :          */
     458           0 :         nr = folio_nr_pages(folio);
     459           0 :         memcg = folio_memcg(folio);
     460           0 :         pgdat = folio_pgdat(folio);
     461           0 :         lruvec = mem_cgroup_lruvec(memcg, pgdat);
     462             : 
     463           0 :         mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
     464             : 
     465             :         mem_cgroup_flush_stats_delayed();
     466             :         /*
     467             :          * Compare the distance to the existing workingset size. We
     468             :          * don't activate pages that couldn't stay resident even if
     469             :          * all the memory was available to the workingset. Whether
     470             :          * workingset competition needs to consider anon or not depends
     471             :          * on having swap.
     472             :          */
     473           0 :         workingset_size = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);
     474           0 :         if (!file) {
     475           0 :                 workingset_size += lruvec_page_state(eviction_lruvec,
     476             :                                                      NR_INACTIVE_FILE);
     477             :         }
     478           0 :         if (mem_cgroup_get_nr_swap_pages(eviction_memcg) > 0) {
     479           0 :                 workingset_size += lruvec_page_state(eviction_lruvec,
     480             :                                                      NR_ACTIVE_ANON);
     481           0 :                 if (file) {
     482           0 :                         workingset_size += lruvec_page_state(eviction_lruvec,
     483             :                                                      NR_INACTIVE_ANON);
     484             :                 }
     485             :         }
     486           0 :         if (refault_distance > workingset_size)
     487             :                 goto out;
     488             : 
     489           0 :         folio_set_active(folio);
     490           0 :         workingset_age_nonresident(lruvec, nr);
     491           0 :         mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file, nr);
     492             : 
     493             :         /* Folio was active prior to eviction */
     494           0 :         if (workingset) {
     495           0 :                 folio_set_workingset(folio);
     496             :                 /*
     497             :                  * XXX: Move to folio_add_lru() when it supports new vs
     498             :                  * putback
     499             :                  */
     500           0 :                 lru_note_cost_refault(folio);
     501           0 :                 mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
     502             :         }
     503             : out:
     504             :         rcu_read_unlock();
     505             : }
     506             : 
     507             : /**
     508             :  * workingset_activation - note a page activation
     509             :  * @folio: Folio that is being activated.
     510             :  */
     511           0 : void workingset_activation(struct folio *folio)
     512             : {
     513             :         struct mem_cgroup *memcg;
     514             : 
     515             :         rcu_read_lock();
     516             :         /*
     517             :          * Filter non-memcg pages here, e.g. unmap can call
     518             :          * mark_page_accessed() on VDSO pages.
     519             :          *
     520             :          * XXX: See workingset_refault() - this should return
     521             :          * root_mem_cgroup even for !CONFIG_MEMCG.
     522             :          */
     523           0 :         memcg = folio_memcg_rcu(folio);
     524             :         if (!mem_cgroup_disabled() && !memcg)
     525             :                 goto out;
     526           0 :         workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio));
     527             : out:
     528             :         rcu_read_unlock();
     529           0 : }
     530             : 
     531             : /*
     532             :  * Shadow entries reflect the share of the working set that does not
     533             :  * fit into memory, so their number depends on the access pattern of
     534             :  * the workload.  In most cases, they will refault or get reclaimed
     535             :  * along with the inode, but a (malicious) workload that streams
     536             :  * through files with a total size several times that of available
     537             :  * memory, while preventing the inodes from being reclaimed, can
     538             :  * create excessive amounts of shadow nodes.  To keep a lid on this,
     539             :  * track shadow nodes and reclaim them when they grow way past the
     540             :  * point where they would still be useful.
     541             :  */
     542             : 
     543             : struct list_lru shadow_nodes;
     544             : 
     545           0 : void workingset_update_node(struct xa_node *node)
     546             : {
     547             :         struct address_space *mapping;
     548             : 
     549             :         /*
     550             :          * Track non-empty nodes that contain only shadow entries;
     551             :          * unlink those that contain pages or are being freed.
     552             :          *
     553             :          * Avoid acquiring the list_lru lock when the nodes are
     554             :          * already where they should be. The list_empty() test is safe
     555             :          * as node->private_list is protected by the i_pages lock.
     556             :          */
     557           0 :         mapping = container_of(node->array, struct address_space, i_pages);
     558             :         lockdep_assert_held(&mapping->i_pages.xa_lock);
     559             : 
     560           0 :         if (node->count && node->count == node->nr_values) {
     561           0 :                 if (list_empty(&node->private_list)) {
     562           0 :                         list_lru_add(&shadow_nodes, &node->private_list);
     563             :                         __inc_lruvec_kmem_state(node, WORKINGSET_NODES);
     564             :                 }
     565             :         } else {
     566           0 :                 if (!list_empty(&node->private_list)) {
     567           0 :                         list_lru_del(&shadow_nodes, &node->private_list);
     568             :                         __dec_lruvec_kmem_state(node, WORKINGSET_NODES);
     569             :                 }
     570             :         }
     571           0 : }
     572             : 
     573           0 : static unsigned long count_shadow_nodes(struct shrinker *shrinker,
     574             :                                         struct shrink_control *sc)
     575             : {
     576             :         unsigned long max_nodes;
     577             :         unsigned long nodes;
     578             :         unsigned long pages;
     579             : 
     580           0 :         nodes = list_lru_shrink_count(&shadow_nodes, sc);
     581           0 :         if (!nodes)
     582             :                 return SHRINK_EMPTY;
     583             : 
     584             :         /*
     585             :          * Approximate a reasonable limit for the nodes
     586             :          * containing shadow entries. We don't need to keep more
     587             :          * shadow entries than possible pages on the active list,
     588             :          * since refault distances bigger than that are dismissed.
     589             :          *
     590             :          * The size of the active list converges toward 100% of
     591             :          * overall page cache as memory grows, with only a tiny
     592             :          * inactive list. Assume the total cache size for that.
     593             :          *
     594             :          * Nodes might be sparsely populated, with only one shadow
     595             :          * entry in the extreme case. Obviously, we cannot keep one
     596             :          * node for every eligible shadow entry, so compromise on a
     597             :          * worst-case density of 1/8th. Below that, not all eligible
     598             :          * refaults can be detected anymore.
     599             :          *
     600             :          * On 64-bit with 7 xa_nodes per page and 64 slots
     601             :          * each, this will reclaim shadow entries when they consume
     602             :          * ~1.8% of available memory:
     603             :          *
     604             :          * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
     605             :          */
     606             : #ifdef CONFIG_MEMCG
     607             :         if (sc->memcg) {
     608             :                 struct lruvec *lruvec;
     609             :                 int i;
     610             : 
     611             :                 lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
     612             :                 for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
     613             :                         pages += lruvec_page_state_local(lruvec,
     614             :                                                          NR_LRU_BASE + i);
     615             :                 pages += lruvec_page_state_local(
     616             :                         lruvec, NR_SLAB_RECLAIMABLE_B) >> PAGE_SHIFT;
     617             :                 pages += lruvec_page_state_local(
     618             :                         lruvec, NR_SLAB_UNRECLAIMABLE_B) >> PAGE_SHIFT;
     619             :         } else
     620             : #endif
     621           0 :                 pages = node_present_pages(sc->nid);
     622             : 
     623           0 :         max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
     624             : 
     625           0 :         if (nodes <= max_nodes)
     626             :                 return 0;
     627           0 :         return nodes - max_nodes;
     628             : }
     629             : 
     630           0 : static enum lru_status shadow_lru_isolate(struct list_head *item,
     631             :                                           struct list_lru_one *lru,
     632             :                                           spinlock_t *lru_lock,
     633             :                                           void *arg) __must_hold(lru_lock)
     634             : {
     635           0 :         struct xa_node *node = container_of(item, struct xa_node, private_list);
     636             :         struct address_space *mapping;
     637             :         int ret;
     638             : 
     639             :         /*
     640             :          * Page cache insertions and deletions synchronously maintain
     641             :          * the shadow node LRU under the i_pages lock and the
     642             :          * lru_lock.  Because the page cache tree is emptied before
     643             :          * the inode can be destroyed, holding the lru_lock pins any
     644             :          * address_space that has nodes on the LRU.
     645             :          *
     646             :          * We can then safely transition to the i_pages lock to
     647             :          * pin only the address_space of the particular node we want
     648             :          * to reclaim, take the node off-LRU, and drop the lru_lock.
     649             :          */
     650             : 
     651           0 :         mapping = container_of(node->array, struct address_space, i_pages);
     652             : 
     653             :         /* Coming from the list, invert the lock order */
     654           0 :         if (!xa_trylock(&mapping->i_pages)) {
     655             :                 spin_unlock_irq(lru_lock);
     656             :                 ret = LRU_RETRY;
     657             :                 goto out;
     658             :         }
     659             : 
     660             :         /* For page cache we need to hold i_lock */
     661           0 :         if (mapping->host != NULL) {
     662           0 :                 if (!spin_trylock(&mapping->host->i_lock)) {
     663             :                         xa_unlock(&mapping->i_pages);
     664             :                         spin_unlock_irq(lru_lock);
     665             :                         ret = LRU_RETRY;
     666             :                         goto out;
     667             :                 }
     668             :         }
     669             : 
     670           0 :         list_lru_isolate(lru, item);
     671           0 :         __dec_lruvec_kmem_state(node, WORKINGSET_NODES);
     672             : 
     673           0 :         spin_unlock(lru_lock);
     674             : 
     675             :         /*
     676             :          * The nodes should only contain one or more shadow entries,
     677             :          * no pages, so we expect to be able to remove them all and
     678             :          * delete and free the empty node afterwards.
     679             :          */
     680           0 :         if (WARN_ON_ONCE(!node->nr_values))
     681             :                 goto out_invalid;
     682           0 :         if (WARN_ON_ONCE(node->count != node->nr_values))
     683             :                 goto out_invalid;
     684           0 :         xa_delete_node(node, workingset_update_node);
     685             :         __inc_lruvec_kmem_state(node, WORKINGSET_NODERECLAIM);
     686             : 
     687             : out_invalid:
     688           0 :         xa_unlock_irq(&mapping->i_pages);
     689           0 :         if (mapping->host != NULL) {
     690           0 :                 if (mapping_shrinkable(mapping))
     691           0 :                         inode_add_lru(mapping->host);
     692           0 :                 spin_unlock(&mapping->host->i_lock);
     693             :         }
     694           0 :         ret = LRU_REMOVED_RETRY;
     695             : out:
     696           0 :         cond_resched();
     697           0 :         spin_lock_irq(lru_lock);
     698           0 :         return ret;
     699             : }
     700             : 
     701           0 : static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
     702             :                                        struct shrink_control *sc)
     703             : {
     704             :         /* list_lru lock nests inside the IRQ-safe i_pages lock */
     705           0 :         return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
     706             :                                         NULL);
     707             : }
     708             : 
     709             : static struct shrinker workingset_shadow_shrinker = {
     710             :         .count_objects = count_shadow_nodes,
     711             :         .scan_objects = scan_shadow_nodes,
     712             :         .seeks = 0, /* ->count reports only fully expendable nodes */
     713             :         .flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
     714             : };
     715             : 
     716             : /*
     717             :  * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
     718             :  * i_pages lock.
     719             :  */
     720             : static struct lock_class_key shadow_nodes_key;
     721             : 
     722           1 : static int __init workingset_init(void)
     723             : {
     724             :         unsigned int timestamp_bits;
     725             :         unsigned int max_order;
     726             :         int ret;
     727             : 
     728             :         BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
     729             :         /*
     730             :          * Calculate the eviction bucket size to cover the longest
     731             :          * actionable refault distance, which is currently half of
     732             :          * memory (totalram_pages/2). However, memory hotplug may add
     733             :          * some more pages at runtime, so keep working with up to
     734             :          * double the initial memory by using totalram_pages as-is.
     735             :          */
     736           1 :         timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
     737           2 :         max_order = fls_long(totalram_pages() - 1);
     738           1 :         if (max_order > timestamp_bits)
     739           0 :                 bucket_order = max_order - timestamp_bits;
     740           1 :         pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
     741             :                timestamp_bits, max_order, bucket_order);
     742             : 
     743           1 :         ret = prealloc_shrinker(&workingset_shadow_shrinker, "mm-shadow");
     744           1 :         if (ret)
     745             :                 goto err;
     746           1 :         ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
     747             :                               &workingset_shadow_shrinker);
     748           1 :         if (ret)
     749             :                 goto err_list_lru;
     750           1 :         register_shrinker_prepared(&workingset_shadow_shrinker);
     751           1 :         return 0;
     752             : err_list_lru:
     753           0 :         free_prealloced_shrinker(&workingset_shadow_shrinker);
     754             : err:
     755             :         return ret;
     756             : }
     757             : module_init(workingset_init);

Generated by: LCOV version 1.14