LCOV - code coverage report
Current view: top level - mm - workingset.c (source / functions) Hit Total Coverage
Test: combined.info Lines: 34 154 22.1 %
Date: 2022-03-28 13:20:08 Functions: 3 8 37.5 %
Branches: 8 42 19.0 %

           Branch data     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/writeback.h>
      10                 :            : #include <linux/shmem_fs.h>
      11                 :            : #include <linux/pagemap.h>
      12                 :            : #include <linux/atomic.h>
      13                 :            : #include <linux/module.h>
      14                 :            : #include <linux/swap.h>
      15                 :            : #include <linux/dax.h>
      16                 :            : #include <linux/fs.h>
      17                 :            : #include <linux/mm.h>
      18                 :            : 
      19                 :            : /*
      20                 :            :  *              Double CLOCK lists
      21                 :            :  *
      22                 :            :  * Per node, two clock lists are maintained for file pages: the
      23                 :            :  * inactive and the active list.  Freshly faulted pages start out at
      24                 :            :  * the head of the inactive list and page reclaim scans pages from the
      25                 :            :  * tail.  Pages that are accessed multiple times on the inactive list
      26                 :            :  * are promoted to the active list, to protect them from reclaim,
      27                 :            :  * whereas active pages are demoted to the inactive list when the
      28                 :            :  * active list grows too big.
      29                 :            :  *
      30                 :            :  *   fault ------------------------+
      31                 :            :  *                                 |
      32                 :            :  *              +--------------+   |            +-------------+
      33                 :            :  *   reclaim <- |   inactive   | <-+-- demotion |    active   | <--+
      34                 :            :  *              +--------------+                +-------------+    |
      35                 :            :  *                     |                                           |
      36                 :            :  *                     +-------------- promotion ------------------+
      37                 :            :  *
      38                 :            :  *
      39                 :            :  *              Access frequency and refault distance
      40                 :            :  *
      41                 :            :  * A workload is thrashing when its pages are frequently used but they
      42                 :            :  * are evicted from the inactive list every time before another access
      43                 :            :  * would have promoted them to the active list.
      44                 :            :  *
      45                 :            :  * In cases where the average access distance between thrashing pages
      46                 :            :  * is bigger than the size of memory there is nothing that can be
      47                 :            :  * done - the thrashing set could never fit into memory under any
      48                 :            :  * circumstance.
      49                 :            :  *
      50                 :            :  * However, the average access distance could be bigger than the
      51                 :            :  * inactive list, yet smaller than the size of memory.  In this case,
      52                 :            :  * the set could fit into memory if it weren't for the currently
      53                 :            :  * active pages - which may be used more, hopefully less frequently:
      54                 :            :  *
      55                 :            :  *      +-memory available to cache-+
      56                 :            :  *      |                           |
      57                 :            :  *      +-inactive------+-active----+
      58                 :            :  *  a b | c d e f g h i | J K L M N |
      59                 :            :  *      +---------------+-----------+
      60                 :            :  *
      61                 :            :  * It is prohibitively expensive to accurately track access frequency
      62                 :            :  * of pages.  But a reasonable approximation can be made to measure
      63                 :            :  * thrashing on the inactive list, after which refaulting pages can be
      64                 :            :  * activated optimistically to compete with the existing active pages.
      65                 :            :  *
      66                 :            :  * Approximating inactive page access frequency - Observations:
      67                 :            :  *
      68                 :            :  * 1. When a page is accessed for the first time, it is added to the
      69                 :            :  *    head of the inactive list, slides every existing inactive page
      70                 :            :  *    towards the tail by one slot, and pushes the current tail page
      71                 :            :  *    out of memory.
      72                 :            :  *
      73                 :            :  * 2. When a page is accessed for the second time, it is promoted to
      74                 :            :  *    the active list, shrinking the inactive list by one slot.  This
      75                 :            :  *    also slides all inactive pages that were faulted into the cache
      76                 :            :  *    more recently than the activated page towards the tail of the
      77                 :            :  *    inactive list.
      78                 :            :  *
      79                 :            :  * Thus:
      80                 :            :  *
      81                 :            :  * 1. The sum of evictions and activations between any two points in
      82                 :            :  *    time indicate the minimum number of inactive pages accessed in
      83                 :            :  *    between.
      84                 :            :  *
      85                 :            :  * 2. Moving one inactive page N page slots towards the tail of the
      86                 :            :  *    list requires at least N inactive page accesses.
      87                 :            :  *
      88                 :            :  * Combining these:
      89                 :            :  *
      90                 :            :  * 1. When a page is finally evicted from memory, the number of
      91                 :            :  *    inactive pages accessed while the page was in cache is at least
      92                 :            :  *    the number of page slots on the inactive list.
      93                 :            :  *
      94                 :            :  * 2. In addition, measuring the sum of evictions and activations (E)
      95                 :            :  *    at the time of a page's eviction, and comparing it to another
      96                 :            :  *    reading (R) at the time the page faults back into memory tells
      97                 :            :  *    the minimum number of accesses while the page was not cached.
      98                 :            :  *    This is called the refault distance.
      99                 :            :  *
     100                 :            :  * Because the first access of the page was the fault and the second
     101                 :            :  * access the refault, we combine the in-cache distance with the
     102                 :            :  * out-of-cache distance to get the complete minimum access distance
     103                 :            :  * of this page:
     104                 :            :  *
     105                 :            :  *      NR_inactive + (R - E)
     106                 :            :  *
     107                 :            :  * And knowing the minimum access distance of a page, we can easily
     108                 :            :  * tell if the page would be able to stay in cache assuming all page
     109                 :            :  * slots in the cache were available:
     110                 :            :  *
     111                 :            :  *   NR_inactive + (R - E) <= NR_inactive + NR_active
     112                 :            :  *
     113                 :            :  * which can be further simplified to
     114                 :            :  *
     115                 :            :  *   (R - E) <= NR_active
     116                 :            :  *
     117                 :            :  * Put into words, the refault distance (out-of-cache) can be seen as
     118                 :            :  * a deficit in inactive list space (in-cache).  If the inactive list
     119                 :            :  * had (R - E) more page slots, the page would not have been evicted
     120                 :            :  * in between accesses, but activated instead.  And on a full system,
     121                 :            :  * the only thing eating into inactive list space is active pages.
     122                 :            :  *
     123                 :            :  *
     124                 :            :  *              Refaulting inactive pages
     125                 :            :  *
     126                 :            :  * All that is known about the active list is that the pages have been
     127                 :            :  * accessed more than once in the past.  This means that at any given
     128                 :            :  * time there is actually a good chance that pages on the active list
     129                 :            :  * are no longer in active use.
     130                 :            :  *
     131                 :            :  * So when a refault distance of (R - E) is observed and there are at
     132                 :            :  * least (R - E) active pages, the refaulting page is activated
     133                 :            :  * optimistically in the hope that (R - E) active pages are actually
     134                 :            :  * used less frequently than the refaulting page - or even not used at
     135                 :            :  * all anymore.
     136                 :            :  *
     137                 :            :  * That means if inactive cache is refaulting with a suitable refault
     138                 :            :  * distance, we assume the cache workingset is transitioning and put
     139                 :            :  * pressure on the current active list.
     140                 :            :  *
     141                 :            :  * If this is wrong and demotion kicks in, the pages which are truly
     142                 :            :  * used more frequently will be reactivated while the less frequently
     143                 :            :  * used once will be evicted from memory.
     144                 :            :  *
     145                 :            :  * But if this is right, the stale pages will be pushed out of memory
     146                 :            :  * and the used pages get to stay in cache.
     147                 :            :  *
     148                 :            :  *              Refaulting active pages
     149                 :            :  *
     150                 :            :  * If on the other hand the refaulting pages have recently been
     151                 :            :  * deactivated, it means that the active list is no longer protecting
     152                 :            :  * actively used cache from reclaim. The cache is NOT transitioning to
     153                 :            :  * a different workingset; the existing workingset is thrashing in the
     154                 :            :  * space allocated to the page cache.
     155                 :            :  *
     156                 :            :  *
     157                 :            :  *              Implementation
     158                 :            :  *
     159                 :            :  * For each node's file LRU lists, a counter for inactive evictions
     160                 :            :  * and activations is maintained (node->inactive_age).
     161                 :            :  *
     162                 :            :  * On eviction, a snapshot of this counter (along with some bits to
     163                 :            :  * identify the node) is stored in the now empty page cache
     164                 :            :  * slot of the evicted page.  This is called a shadow entry.
     165                 :            :  *
     166                 :            :  * On cache misses for which there are shadow entries, an eligible
     167                 :            :  * refault distance will immediately activate the refaulting page.
     168                 :            :  */
     169                 :            : 
     170                 :            : #define EVICTION_SHIFT  ((BITS_PER_LONG - BITS_PER_XA_VALUE) +  \
     171                 :            :                          1 + NODES_SHIFT + MEM_CGROUP_ID_SHIFT)
     172                 :            : #define EVICTION_MASK   (~0UL >> EVICTION_SHIFT)
     173                 :            : 
     174                 :            : /*
     175                 :            :  * Eviction timestamps need to be able to cover the full range of
     176                 :            :  * actionable refaults. However, bits are tight in the xarray
     177                 :            :  * entry, and after storing the identifier for the lruvec there might
     178                 :            :  * not be enough left to represent every single actionable refault. In
     179                 :            :  * that case, we have to sacrifice granularity for distance, and group
     180                 :            :  * evictions into coarser buckets by shaving off lower timestamp bits.
     181                 :            :  */
     182                 :            : static unsigned int bucket_order __read_mostly;
     183                 :            : 
     184                 :          0 : static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
     185                 :            :                          bool workingset)
     186                 :            : {
     187                 :          0 :         eviction >>= bucket_order;
     188                 :          0 :         eviction &= EVICTION_MASK;
     189                 :          0 :         eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
     190                 :          0 :         eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
     191                 :          0 :         eviction = (eviction << 1) | workingset;
     192                 :            : 
     193         [ #  # ]:          0 :         return xa_mk_value(eviction);
     194                 :            : }
     195                 :            : 
     196                 :          0 : static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
     197                 :            :                           unsigned long *evictionp, bool *workingsetp)
     198                 :            : {
     199                 :          0 :         unsigned long entry = xa_to_value(shadow);
     200                 :          0 :         int memcgid, nid;
     201                 :          0 :         bool workingset;
     202                 :            : 
     203                 :          0 :         workingset = entry & 1;
     204                 :          0 :         entry >>= 1;
     205                 :          0 :         nid = entry & ((1UL << NODES_SHIFT) - 1);
     206                 :          0 :         entry >>= NODES_SHIFT;
     207                 :          0 :         memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
     208                 :          0 :         entry >>= MEM_CGROUP_ID_SHIFT;
     209                 :            : 
     210                 :          0 :         *memcgidp = memcgid;
     211                 :          0 :         *pgdat = NODE_DATA(nid);
     212                 :          0 :         *evictionp = entry << bucket_order;
     213                 :          0 :         *workingsetp = workingset;
     214                 :            : }
     215                 :            : 
     216                 :     138850 : static void advance_inactive_age(struct mem_cgroup *memcg, pg_data_t *pgdat)
     217                 :            : {
     218                 :            :         /*
     219                 :            :          * Reclaiming a cgroup means reclaiming all its children in a
     220                 :            :          * round-robin fashion. That means that each cgroup has an LRU
     221                 :            :          * order that is composed of the LRU orders of its child
     222                 :            :          * cgroups; and every page has an LRU position not just in the
     223                 :            :          * cgroup that owns it, but in all of that group's ancestors.
     224                 :            :          *
     225                 :            :          * So when the physical inactive list of a leaf cgroup ages,
     226                 :            :          * the virtual inactive lists of all its parents, including
     227                 :            :          * the root cgroup's, age as well.
     228                 :            :          */
     229                 :     138850 :         do {
     230                 :     138850 :                 struct lruvec *lruvec;
     231                 :            : 
     232                 :     138850 :                 lruvec = mem_cgroup_lruvec(memcg, pgdat);
     233                 :     138850 :                 atomic_long_inc(&lruvec->inactive_age);
     234                 :     138850 :         } while (memcg && (memcg = parent_mem_cgroup(memcg)));
     235                 :            : }
     236                 :            : 
     237                 :            : /**
     238                 :            :  * workingset_eviction - note the eviction of a page from memory
     239                 :            :  * @target_memcg: the cgroup that is causing the reclaim
     240                 :            :  * @page: the page being evicted
     241                 :            :  *
     242                 :            :  * Returns a shadow entry to be stored in @page->mapping->i_pages in place
     243                 :            :  * of the evicted @page so that a later refault can be detected.
     244                 :            :  */
     245                 :          0 : void *workingset_eviction(struct page *page, struct mem_cgroup *target_memcg)
     246                 :            : {
     247                 :          0 :         struct pglist_data *pgdat = page_pgdat(page);
     248                 :          0 :         unsigned long eviction;
     249                 :          0 :         struct lruvec *lruvec;
     250                 :          0 :         int memcgid;
     251                 :            : 
     252                 :            :         /* Page is fully exclusive and pins page->mem_cgroup */
     253                 :          0 :         VM_BUG_ON_PAGE(PageLRU(page), page);
     254                 :          0 :         VM_BUG_ON_PAGE(page_count(page), page);
     255                 :          0 :         VM_BUG_ON_PAGE(!PageLocked(page), page);
     256                 :            : 
     257                 :          0 :         advance_inactive_age(page_memcg(page), pgdat);
     258                 :            : 
     259                 :          0 :         lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
     260                 :            :         /* XXX: target_memcg can be NULL, go through lruvec */
     261                 :          0 :         memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
     262                 :          0 :         eviction = atomic_long_read(&lruvec->inactive_age);
     263         [ #  # ]:          0 :         return pack_shadow(memcgid, pgdat, eviction, PageWorkingset(page));
     264                 :            : }
     265                 :            : 
     266                 :            : /**
     267                 :            :  * workingset_refault - evaluate the refault of a previously evicted page
     268                 :            :  * @page: the freshly allocated replacement page
     269                 :            :  * @shadow: shadow entry of the evicted page
     270                 :            :  *
     271                 :            :  * Calculates and evaluates the refault distance of the previously
     272                 :            :  * evicted page in the context of the node and the memcg whose memory
     273                 :            :  * pressure caused the eviction.
     274                 :            :  */
     275                 :          0 : void workingset_refault(struct page *page, void *shadow)
     276                 :            : {
     277                 :          0 :         struct mem_cgroup *eviction_memcg;
     278                 :          0 :         struct lruvec *eviction_lruvec;
     279                 :          0 :         unsigned long refault_distance;
     280                 :          0 :         struct pglist_data *pgdat;
     281                 :          0 :         unsigned long active_file;
     282                 :          0 :         struct mem_cgroup *memcg;
     283                 :          0 :         unsigned long eviction;
     284                 :          0 :         struct lruvec *lruvec;
     285                 :          0 :         unsigned long refault;
     286                 :          0 :         bool workingset;
     287                 :          0 :         int memcgid;
     288                 :            : 
     289                 :          0 :         unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
     290                 :            : 
     291                 :          0 :         rcu_read_lock();
     292                 :            :         /*
     293                 :            :          * Look up the memcg associated with the stored ID. It might
     294                 :            :          * have been deleted since the page's eviction.
     295                 :            :          *
     296                 :            :          * Note that in rare events the ID could have been recycled
     297                 :            :          * for a new cgroup that refaults a shared page. This is
     298                 :            :          * impossible to tell from the available data. However, this
     299                 :            :          * should be a rare and limited disturbance, and activations
     300                 :            :          * are always speculative anyway. Ultimately, it's the aging
     301                 :            :          * algorithm's job to shake out the minimum access frequency
     302                 :            :          * for the active cache.
     303                 :            :          *
     304                 :            :          * XXX: On !CONFIG_MEMCG, this will always return NULL; it
     305                 :            :          * would be better if the root_mem_cgroup existed in all
     306                 :            :          * configurations instead.
     307                 :            :          */
     308                 :          0 :         eviction_memcg = mem_cgroup_from_id(memcgid);
     309                 :          0 :         if (!mem_cgroup_disabled() && !eviction_memcg)
     310                 :            :                 goto out;
     311                 :          0 :         eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
     312                 :          0 :         refault = atomic_long_read(&eviction_lruvec->inactive_age);
     313                 :          0 :         active_file = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);
     314                 :            : 
     315                 :            :         /*
     316                 :            :          * Calculate the refault distance
     317                 :            :          *
     318                 :            :          * The unsigned subtraction here gives an accurate distance
     319                 :            :          * across inactive_age overflows in most cases. There is a
     320                 :            :          * special case: usually, shadow entries have a short lifetime
     321                 :            :          * and are either refaulted or reclaimed along with the inode
     322                 :            :          * before they get too old.  But it is not impossible for the
     323                 :            :          * inactive_age to lap a shadow entry in the field, which can
     324                 :            :          * then result in a false small refault distance, leading to a
     325                 :            :          * false activation should this old entry actually refault
     326                 :            :          * again.  However, earlier kernels used to deactivate
     327                 :            :          * unconditionally with *every* reclaim invocation for the
     328                 :            :          * longest time, so the occasional inappropriate activation
     329                 :            :          * leading to pressure on the active list is not a problem.
     330                 :            :          */
     331                 :          0 :         refault_distance = (refault - eviction) & EVICTION_MASK;
     332                 :            : 
     333                 :            :         /*
     334                 :            :          * The activation decision for this page is made at the level
     335                 :            :          * where the eviction occurred, as that is where the LRU order
     336                 :            :          * during page reclaim is being determined.
     337                 :            :          *
     338                 :            :          * However, the cgroup that will own the page is the one that
     339                 :            :          * is actually experiencing the refault event.
     340                 :            :          */
     341                 :          0 :         memcg = page_memcg(page);
     342                 :          0 :         lruvec = mem_cgroup_lruvec(memcg, pgdat);
     343                 :            : 
     344                 :          0 :         inc_lruvec_state(lruvec, WORKINGSET_REFAULT);
     345                 :            : 
     346                 :            :         /*
     347                 :            :          * Compare the distance to the existing workingset size. We
     348                 :            :          * don't act on pages that couldn't stay resident even if all
     349                 :            :          * the memory was available to the page cache.
     350                 :            :          */
     351         [ #  # ]:          0 :         if (refault_distance > active_file)
     352                 :          0 :                 goto out;
     353                 :            : 
     354         [ #  # ]:          0 :         SetPageActive(page);
     355                 :          0 :         advance_inactive_age(memcg, pgdat);
     356                 :          0 :         inc_lruvec_state(lruvec, WORKINGSET_ACTIVATE);
     357                 :            : 
     358                 :            :         /* Page was active prior to eviction */
     359         [ #  # ]:          0 :         if (workingset) {
     360         [ #  # ]:          0 :                 SetPageWorkingset(page);
     361                 :          0 :                 inc_lruvec_state(lruvec, WORKINGSET_RESTORE);
     362                 :            :         }
     363                 :          0 : out:
     364                 :          0 :         rcu_read_unlock();
     365                 :          0 : }
     366                 :            : 
     367                 :            : /**
     368                 :            :  * workingset_activation - note a page activation
     369                 :            :  * @page: page that is being activated
     370                 :            :  */
     371                 :     138850 : void workingset_activation(struct page *page)
     372                 :            : {
     373                 :     138850 :         struct mem_cgroup *memcg;
     374                 :            : 
     375                 :     138850 :         rcu_read_lock();
     376                 :            :         /*
     377                 :            :          * Filter non-memcg pages here, e.g. unmap can call
     378                 :            :          * mark_page_accessed() on VDSO pages.
     379                 :            :          *
     380                 :            :          * XXX: See workingset_refault() - this should return
     381                 :            :          * root_mem_cgroup even for !CONFIG_MEMCG.
     382                 :            :          */
     383                 :     138850 :         memcg = page_memcg_rcu(page);
     384                 :     138850 :         if (!mem_cgroup_disabled() && !memcg)
     385                 :            :                 goto out;
     386                 :     138850 :         advance_inactive_age(memcg, page_pgdat(page));
     387                 :            : out:
     388                 :     138850 :         rcu_read_unlock();
     389                 :     138850 : }
     390                 :            : 
     391                 :            : /*
     392                 :            :  * Shadow entries reflect the share of the working set that does not
     393                 :            :  * fit into memory, so their number depends on the access pattern of
     394                 :            :  * the workload.  In most cases, they will refault or get reclaimed
     395                 :            :  * along with the inode, but a (malicious) workload that streams
     396                 :            :  * through files with a total size several times that of available
     397                 :            :  * memory, while preventing the inodes from being reclaimed, can
     398                 :            :  * create excessive amounts of shadow nodes.  To keep a lid on this,
     399                 :            :  * track shadow nodes and reclaim them when they grow way past the
     400                 :            :  * point where they would still be useful.
     401                 :            :  */
     402                 :            : 
     403                 :            : static struct list_lru shadow_nodes;
     404                 :            : 
     405                 :     541889 : void workingset_update_node(struct xa_node *node)
     406                 :            : {
     407                 :            :         /*
     408                 :            :          * Track non-empty nodes that contain only shadow entries;
     409                 :            :          * unlink those that contain pages or are being freed.
     410                 :            :          *
     411                 :            :          * Avoid acquiring the list_lru lock when the nodes are
     412                 :            :          * already where they should be. The list_empty() test is safe
     413                 :            :          * as node->private_list is protected by the i_pages lock.
     414                 :            :          */
     415                 :     541889 :         VM_WARN_ON_ONCE(!irqs_disabled());  /* For __inc_lruvec_page_state */
     416                 :            : 
     417   [ +  +  -  + ]:     541889 :         if (node->count && node->count == node->nr_values) {
     418         [ #  # ]:          0 :                 if (list_empty(&node->private_list)) {
     419                 :          0 :                         list_lru_add(&shadow_nodes, &node->private_list);
     420                 :          0 :                         __inc_lruvec_slab_state(node, WORKINGSET_NODES);
     421                 :            :                 }
     422                 :            :         } else {
     423         [ -  + ]:     541889 :                 if (!list_empty(&node->private_list)) {
     424                 :          0 :                         list_lru_del(&shadow_nodes, &node->private_list);
     425                 :          0 :                         __dec_lruvec_slab_state(node, WORKINGSET_NODES);
     426                 :            :                 }
     427                 :            :         }
     428                 :     541889 : }
     429                 :            : 
     430                 :          0 : static unsigned long count_shadow_nodes(struct shrinker *shrinker,
     431                 :            :                                         struct shrink_control *sc)
     432                 :            : {
     433                 :          0 :         unsigned long max_nodes;
     434                 :          0 :         unsigned long nodes;
     435                 :          0 :         unsigned long pages;
     436                 :            : 
     437                 :          0 :         nodes = list_lru_shrink_count(&shadow_nodes, sc);
     438                 :            : 
     439                 :            :         /*
     440                 :            :          * Approximate a reasonable limit for the nodes
     441                 :            :          * containing shadow entries. We don't need to keep more
     442                 :            :          * shadow entries than possible pages on the active list,
     443                 :            :          * since refault distances bigger than that are dismissed.
     444                 :            :          *
     445                 :            :          * The size of the active list converges toward 100% of
     446                 :            :          * overall page cache as memory grows, with only a tiny
     447                 :            :          * inactive list. Assume the total cache size for that.
     448                 :            :          *
     449                 :            :          * Nodes might be sparsely populated, with only one shadow
     450                 :            :          * entry in the extreme case. Obviously, we cannot keep one
     451                 :            :          * node for every eligible shadow entry, so compromise on a
     452                 :            :          * worst-case density of 1/8th. Below that, not all eligible
     453                 :            :          * refaults can be detected anymore.
     454                 :            :          *
     455                 :            :          * On 64-bit with 7 xa_nodes per page and 64 slots
     456                 :            :          * each, this will reclaim shadow entries when they consume
     457                 :            :          * ~1.8% of available memory:
     458                 :            :          *
     459                 :            :          * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
     460                 :            :          */
     461                 :            : #ifdef CONFIG_MEMCG
     462                 :            :         if (sc->memcg) {
     463                 :            :                 struct lruvec *lruvec;
     464                 :            :                 int i;
     465                 :            : 
     466                 :            :                 lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
     467                 :            :                 for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
     468                 :            :                         pages += lruvec_page_state_local(lruvec,
     469                 :            :                                                          NR_LRU_BASE + i);
     470                 :            :                 pages += lruvec_page_state_local(lruvec, NR_SLAB_RECLAIMABLE);
     471                 :            :                 pages += lruvec_page_state_local(lruvec, NR_SLAB_UNRECLAIMABLE);
     472                 :            :         } else
     473                 :            : #endif
     474                 :          0 :                 pages = node_present_pages(sc->nid);
     475                 :            : 
     476                 :          0 :         max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
     477                 :            : 
     478         [ #  # ]:          0 :         if (!nodes)
     479                 :            :                 return SHRINK_EMPTY;
     480                 :            : 
     481         [ #  # ]:          0 :         if (nodes <= max_nodes)
     482                 :            :                 return 0;
     483                 :          0 :         return nodes - max_nodes;
     484                 :            : }
     485                 :            : 
     486                 :          0 : static enum lru_status shadow_lru_isolate(struct list_head *item,
     487                 :            :                                           struct list_lru_one *lru,
     488                 :            :                                           spinlock_t *lru_lock,
     489                 :            :                                           void *arg) __must_hold(lru_lock)
     490                 :            : {
     491                 :          0 :         struct xa_node *node = container_of(item, struct xa_node, private_list);
     492                 :          0 :         XA_STATE(xas, node->array, 0);
     493                 :          0 :         struct address_space *mapping;
     494                 :          0 :         int ret;
     495                 :            : 
     496                 :            :         /*
     497                 :            :          * Page cache insertions and deletions synchroneously maintain
     498                 :            :          * the shadow node LRU under the i_pages lock and the
     499                 :            :          * lru_lock.  Because the page cache tree is emptied before
     500                 :            :          * the inode can be destroyed, holding the lru_lock pins any
     501                 :            :          * address_space that has nodes on the LRU.
     502                 :            :          *
     503                 :            :          * We can then safely transition to the i_pages lock to
     504                 :            :          * pin only the address_space of the particular node we want
     505                 :            :          * to reclaim, take the node off-LRU, and drop the lru_lock.
     506                 :            :          */
     507                 :            : 
     508                 :          0 :         mapping = container_of(node->array, struct address_space, i_pages);
     509                 :            : 
     510                 :            :         /* Coming from the list, invert the lock order */
     511         [ #  # ]:          0 :         if (!xa_trylock(&mapping->i_pages)) {
     512                 :          0 :                 spin_unlock_irq(lru_lock);
     513                 :          0 :                 ret = LRU_RETRY;
     514                 :          0 :                 goto out;
     515                 :            :         }
     516                 :            : 
     517                 :          0 :         list_lru_isolate(lru, item);
     518                 :          0 :         __dec_lruvec_slab_state(node, WORKINGSET_NODES);
     519                 :            : 
     520                 :          0 :         spin_unlock(lru_lock);
     521                 :            : 
     522                 :            :         /*
     523                 :            :          * The nodes should only contain one or more shadow entries,
     524                 :            :          * no pages, so we expect to be able to remove them all and
     525                 :            :          * delete and free the empty node afterwards.
     526                 :            :          */
     527   [ #  #  #  # ]:          0 :         if (WARN_ON_ONCE(!node->nr_values))
     528                 :          0 :                 goto out_invalid;
     529   [ #  #  #  # ]:          0 :         if (WARN_ON_ONCE(node->count != node->nr_values))
     530                 :          0 :                 goto out_invalid;
     531                 :          0 :         mapping->nrexceptional -= node->nr_values;
     532                 :          0 :         xas.xa_node = xa_parent_locked(&mapping->i_pages, node);
     533                 :          0 :         xas.xa_offset = node->offset;
     534                 :          0 :         xas.xa_shift = node->shift + XA_CHUNK_SHIFT;
     535                 :          0 :         xas_set_update(&xas, workingset_update_node);
     536                 :            :         /*
     537                 :            :          * We could store a shadow entry here which was the minimum of the
     538                 :            :          * shadow entries we were tracking ...
     539                 :            :          */
     540                 :          0 :         xas_store(&xas, NULL);
     541                 :          0 :         __inc_lruvec_slab_state(node, WORKINGSET_NODERECLAIM);
     542                 :            : 
     543                 :          0 : out_invalid:
     544                 :          0 :         xa_unlock_irq(&mapping->i_pages);
     545                 :          0 :         ret = LRU_REMOVED_RETRY;
     546                 :          0 : out:
     547                 :          0 :         cond_resched();
     548                 :          0 :         spin_lock_irq(lru_lock);
     549                 :          0 :         return ret;
     550                 :            : }
     551                 :            : 
     552                 :          0 : static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
     553                 :            :                                        struct shrink_control *sc)
     554                 :            : {
     555                 :            :         /* list_lru lock nests inside the IRQ-safe i_pages lock */
     556                 :          0 :         return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
     557                 :            :                                         NULL);
     558                 :            : }
     559                 :            : 
     560                 :            : static struct shrinker workingset_shadow_shrinker = {
     561                 :            :         .count_objects = count_shadow_nodes,
     562                 :            :         .scan_objects = scan_shadow_nodes,
     563                 :            :         .seeks = 0, /* ->count reports only fully expendable nodes */
     564                 :            :         .flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
     565                 :            : };
     566                 :            : 
     567                 :            : /*
     568                 :            :  * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
     569                 :            :  * i_pages lock.
     570                 :            :  */
     571                 :            : static struct lock_class_key shadow_nodes_key;
     572                 :            : 
     573                 :         30 : static int __init workingset_init(void)
     574                 :            : {
     575                 :         30 :         unsigned int timestamp_bits;
     576                 :         30 :         unsigned int max_order;
     577                 :         30 :         int ret;
     578                 :            : 
     579                 :         30 :         BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
     580                 :            :         /*
     581                 :            :          * Calculate the eviction bucket size to cover the longest
     582                 :            :          * actionable refault distance, which is currently half of
     583                 :            :          * memory (totalram_pages/2). However, memory hotplug may add
     584                 :            :          * some more pages at runtime, so keep working with up to
     585                 :            :          * double the initial memory by using totalram_pages as-is.
     586                 :            :          */
     587                 :         30 :         timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
     588         [ -  + ]:         30 :         max_order = fls_long(totalram_pages() - 1);
     589         [ -  + ]:         30 :         if (max_order > timestamp_bits)
     590                 :          0 :                 bucket_order = max_order - timestamp_bits;
     591                 :         30 :         pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
     592                 :            :                timestamp_bits, max_order, bucket_order);
     593                 :            : 
     594                 :         30 :         ret = prealloc_shrinker(&workingset_shadow_shrinker);
     595         [ -  + ]:         30 :         if (ret)
     596                 :          0 :                 goto err;
     597                 :         30 :         ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
     598                 :            :                               &workingset_shadow_shrinker);
     599         [ -  + ]:         30 :         if (ret)
     600                 :          0 :                 goto err_list_lru;
     601                 :         30 :         register_shrinker_prepared(&workingset_shadow_shrinker);
     602                 :         30 :         return 0;
     603                 :            : err_list_lru:
     604                 :          0 :         free_prealloced_shrinker(&workingset_shadow_shrinker);
     605                 :            : err:
     606                 :            :         return ret;
     607                 :            : }
     608                 :            : module_init(workingset_init);

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