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![Mel Gorman](/assets/img/avatar_default.png)
Working set and refault detection is still zone-based, fix it. Link: http://lkml.kernel.org/r/1467970510-21195-16-git-send-email-mgorman@techsingularity.net Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Hillf Danton <hillf.zj@alibaba-inc.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Minchan Kim <minchan@kernel.org> Cc: Rik van Riel <riel@surriel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
509 lines
17 KiB
C
509 lines
17 KiB
C
/*
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* Workingset detection
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*
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* Copyright (C) 2013 Red Hat, Inc., Johannes Weiner
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*/
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#include <linux/memcontrol.h>
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#include <linux/writeback.h>
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#include <linux/pagemap.h>
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#include <linux/atomic.h>
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#include <linux/module.h>
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#include <linux/swap.h>
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#include <linux/fs.h>
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#include <linux/mm.h>
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/*
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* Double CLOCK lists
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*
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* Per node, two clock lists are maintained for file pages: the
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* inactive and the active list. Freshly faulted pages start out at
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* the head of the inactive list and page reclaim scans pages from the
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* tail. Pages that are accessed multiple times on the inactive list
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* are promoted to the active list, to protect them from reclaim,
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* whereas active pages are demoted to the inactive list when the
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* active list grows too big.
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*
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* fault ------------------------+
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* |
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* +--------------+ | +-------------+
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* reclaim <- | inactive | <-+-- demotion | active | <--+
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* +--------------+ +-------------+ |
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* | |
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* +-------------- promotion ------------------+
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*
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*
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* Access frequency and refault distance
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*
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* A workload is thrashing when its pages are frequently used but they
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* are evicted from the inactive list every time before another access
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* would have promoted them to the active list.
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*
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* In cases where the average access distance between thrashing pages
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* is bigger than the size of memory there is nothing that can be
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* done - the thrashing set could never fit into memory under any
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* circumstance.
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*
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* However, the average access distance could be bigger than the
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* inactive list, yet smaller than the size of memory. In this case,
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* the set could fit into memory if it weren't for the currently
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* active pages - which may be used more, hopefully less frequently:
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*
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* +-memory available to cache-+
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* | |
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* +-inactive------+-active----+
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* a b | c d e f g h i | J K L M N |
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* +---------------+-----------+
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*
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* It is prohibitively expensive to accurately track access frequency
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* of pages. But a reasonable approximation can be made to measure
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* thrashing on the inactive list, after which refaulting pages can be
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* activated optimistically to compete with the existing active pages.
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*
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* Approximating inactive page access frequency - Observations:
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*
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* 1. When a page is accessed for the first time, it is added to the
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* head of the inactive list, slides every existing inactive page
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* towards the tail by one slot, and pushes the current tail page
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* out of memory.
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*
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* 2. When a page is accessed for the second time, it is promoted to
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* the active list, shrinking the inactive list by one slot. This
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* also slides all inactive pages that were faulted into the cache
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* more recently than the activated page towards the tail of the
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* inactive list.
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*
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* Thus:
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*
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* 1. The sum of evictions and activations between any two points in
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* time indicate the minimum number of inactive pages accessed in
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* between.
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*
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* 2. Moving one inactive page N page slots towards the tail of the
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* list requires at least N inactive page accesses.
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*
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* Combining these:
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*
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* 1. When a page is finally evicted from memory, the number of
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* inactive pages accessed while the page was in cache is at least
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* the number of page slots on the inactive list.
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*
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* 2. In addition, measuring the sum of evictions and activations (E)
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* at the time of a page's eviction, and comparing it to another
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* reading (R) at the time the page faults back into memory tells
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* the minimum number of accesses while the page was not cached.
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* This is called the refault distance.
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*
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* Because the first access of the page was the fault and the second
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* access the refault, we combine the in-cache distance with the
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* out-of-cache distance to get the complete minimum access distance
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* of this page:
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*
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* NR_inactive + (R - E)
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*
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* And knowing the minimum access distance of a page, we can easily
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* tell if the page would be able to stay in cache assuming all page
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* slots in the cache were available:
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*
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* NR_inactive + (R - E) <= NR_inactive + NR_active
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*
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* which can be further simplified to
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*
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* (R - E) <= NR_active
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*
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* Put into words, the refault distance (out-of-cache) can be seen as
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* a deficit in inactive list space (in-cache). If the inactive list
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* had (R - E) more page slots, the page would not have been evicted
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* in between accesses, but activated instead. And on a full system,
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* the only thing eating into inactive list space is active pages.
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*
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*
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* Activating refaulting pages
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*
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* All that is known about the active list is that the pages have been
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* accessed more than once in the past. This means that at any given
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* time there is actually a good chance that pages on the active list
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* are no longer in active use.
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*
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* So when a refault distance of (R - E) is observed and there are at
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* least (R - E) active pages, the refaulting page is activated
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* optimistically in the hope that (R - E) active pages are actually
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* used less frequently than the refaulting page - or even not used at
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* all anymore.
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*
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* If this is wrong and demotion kicks in, the pages which are truly
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* used more frequently will be reactivated while the less frequently
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* used once will be evicted from memory.
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*
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* But if this is right, the stale pages will be pushed out of memory
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* and the used pages get to stay in cache.
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*
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*
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* Implementation
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*
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* For each node's file LRU lists, a counter for inactive evictions
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* and activations is maintained (node->inactive_age).
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*
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* On eviction, a snapshot of this counter (along with some bits to
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* identify the node) is stored in the now empty page cache radix tree
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* slot of the evicted page. This is called a shadow entry.
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*
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* On cache misses for which there are shadow entries, an eligible
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* refault distance will immediately activate the refaulting page.
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*/
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#define EVICTION_SHIFT (RADIX_TREE_EXCEPTIONAL_ENTRY + \
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NODES_SHIFT + \
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MEM_CGROUP_ID_SHIFT)
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#define EVICTION_MASK (~0UL >> EVICTION_SHIFT)
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/*
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* Eviction timestamps need to be able to cover the full range of
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* actionable refaults. However, bits are tight in the radix tree
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* entry, and after storing the identifier for the lruvec there might
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* not be enough left to represent every single actionable refault. In
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* that case, we have to sacrifice granularity for distance, and group
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* evictions into coarser buckets by shaving off lower timestamp bits.
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*/
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static unsigned int bucket_order __read_mostly;
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static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction)
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{
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eviction >>= bucket_order;
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eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
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eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
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eviction = (eviction << RADIX_TREE_EXCEPTIONAL_SHIFT);
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return (void *)(eviction | RADIX_TREE_EXCEPTIONAL_ENTRY);
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}
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static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
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unsigned long *evictionp)
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{
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unsigned long entry = (unsigned long)shadow;
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int memcgid, nid;
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entry >>= RADIX_TREE_EXCEPTIONAL_SHIFT;
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nid = entry & ((1UL << NODES_SHIFT) - 1);
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entry >>= NODES_SHIFT;
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memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
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entry >>= MEM_CGROUP_ID_SHIFT;
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*memcgidp = memcgid;
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*pgdat = NODE_DATA(nid);
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*evictionp = entry << bucket_order;
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}
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/**
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* workingset_eviction - note the eviction of a page from memory
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* @mapping: address space the page was backing
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* @page: the page being evicted
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*
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* Returns a shadow entry to be stored in @mapping->page_tree in place
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* of the evicted @page so that a later refault can be detected.
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*/
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void *workingset_eviction(struct address_space *mapping, struct page *page)
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{
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struct mem_cgroup *memcg = page_memcg(page);
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struct pglist_data *pgdat = page_pgdat(page);
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int memcgid = mem_cgroup_id(memcg);
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unsigned long eviction;
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struct lruvec *lruvec;
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/* Page is fully exclusive and pins page->mem_cgroup */
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VM_BUG_ON_PAGE(PageLRU(page), page);
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VM_BUG_ON_PAGE(page_count(page), page);
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VM_BUG_ON_PAGE(!PageLocked(page), page);
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lruvec = mem_cgroup_lruvec(pgdat, memcg);
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eviction = atomic_long_inc_return(&lruvec->inactive_age);
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return pack_shadow(memcgid, pgdat, eviction);
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}
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/**
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* workingset_refault - evaluate the refault of a previously evicted page
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* @shadow: shadow entry of the evicted page
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*
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* Calculates and evaluates the refault distance of the previously
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* evicted page in the context of the node it was allocated in.
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*
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* Returns %true if the page should be activated, %false otherwise.
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*/
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bool workingset_refault(void *shadow)
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{
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unsigned long refault_distance;
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unsigned long active_file;
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struct mem_cgroup *memcg;
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unsigned long eviction;
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struct lruvec *lruvec;
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unsigned long refault;
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struct pglist_data *pgdat;
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int memcgid;
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unpack_shadow(shadow, &memcgid, &pgdat, &eviction);
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rcu_read_lock();
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/*
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* Look up the memcg associated with the stored ID. It might
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* have been deleted since the page's eviction.
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*
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* Note that in rare events the ID could have been recycled
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* for a new cgroup that refaults a shared page. This is
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* impossible to tell from the available data. However, this
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* should be a rare and limited disturbance, and activations
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* are always speculative anyway. Ultimately, it's the aging
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* algorithm's job to shake out the minimum access frequency
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* for the active cache.
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*
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* XXX: On !CONFIG_MEMCG, this will always return NULL; it
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* would be better if the root_mem_cgroup existed in all
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* configurations instead.
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*/
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memcg = mem_cgroup_from_id(memcgid);
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if (!mem_cgroup_disabled() && !memcg) {
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rcu_read_unlock();
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return false;
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}
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lruvec = mem_cgroup_lruvec(pgdat, memcg);
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refault = atomic_long_read(&lruvec->inactive_age);
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active_file = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE);
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rcu_read_unlock();
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/*
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* The unsigned subtraction here gives an accurate distance
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* across inactive_age overflows in most cases.
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*
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* There is a special case: usually, shadow entries have a
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* short lifetime and are either refaulted or reclaimed along
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* with the inode before they get too old. But it is not
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* impossible for the inactive_age to lap a shadow entry in
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* the field, which can then can result in a false small
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* refault distance, leading to a false activation should this
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* old entry actually refault again. However, earlier kernels
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* used to deactivate unconditionally with *every* reclaim
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* invocation for the longest time, so the occasional
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* inappropriate activation leading to pressure on the active
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* list is not a problem.
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*/
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refault_distance = (refault - eviction) & EVICTION_MASK;
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inc_node_state(pgdat, WORKINGSET_REFAULT);
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if (refault_distance <= active_file) {
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inc_node_state(pgdat, WORKINGSET_ACTIVATE);
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return true;
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}
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return false;
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}
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/**
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* workingset_activation - note a page activation
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* @page: page that is being activated
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*/
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void workingset_activation(struct page *page)
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{
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struct mem_cgroup *memcg;
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struct lruvec *lruvec;
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rcu_read_lock();
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/*
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* Filter non-memcg pages here, e.g. unmap can call
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* mark_page_accessed() on VDSO pages.
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*
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* XXX: See workingset_refault() - this should return
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* root_mem_cgroup even for !CONFIG_MEMCG.
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*/
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memcg = page_memcg_rcu(page);
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if (!mem_cgroup_disabled() && !memcg)
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goto out;
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lruvec = mem_cgroup_lruvec(page_pgdat(page), memcg);
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atomic_long_inc(&lruvec->inactive_age);
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out:
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rcu_read_unlock();
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}
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/*
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* Shadow entries reflect the share of the working set that does not
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* fit into memory, so their number depends on the access pattern of
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* the workload. In most cases, they will refault or get reclaimed
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* along with the inode, but a (malicious) workload that streams
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* through files with a total size several times that of available
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* memory, while preventing the inodes from being reclaimed, can
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* create excessive amounts of shadow nodes. To keep a lid on this,
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* track shadow nodes and reclaim them when they grow way past the
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* point where they would still be useful.
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*/
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struct list_lru workingset_shadow_nodes;
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static unsigned long count_shadow_nodes(struct shrinker *shrinker,
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struct shrink_control *sc)
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{
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unsigned long shadow_nodes;
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unsigned long max_nodes;
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unsigned long pages;
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/* list_lru lock nests inside IRQ-safe mapping->tree_lock */
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local_irq_disable();
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shadow_nodes = list_lru_shrink_count(&workingset_shadow_nodes, sc);
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local_irq_enable();
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if (memcg_kmem_enabled()) {
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pages = mem_cgroup_node_nr_lru_pages(sc->memcg, sc->nid,
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LRU_ALL_FILE);
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} else {
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pages = node_page_state(NODE_DATA(sc->nid), NR_ACTIVE_FILE) +
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node_page_state(NODE_DATA(sc->nid), NR_INACTIVE_FILE);
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}
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/*
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* Active cache pages are limited to 50% of memory, and shadow
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* entries that represent a refault distance bigger than that
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* do not have any effect. Limit the number of shadow nodes
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* such that shadow entries do not exceed the number of active
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* cache pages, assuming a worst-case node population density
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* of 1/8th on average.
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*
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* On 64-bit with 7 radix_tree_nodes per page and 64 slots
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* each, this will reclaim shadow entries when they consume
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* ~2% of available memory:
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*
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* PAGE_SIZE / radix_tree_nodes / node_entries / PAGE_SIZE
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*/
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max_nodes = pages >> (1 + RADIX_TREE_MAP_SHIFT - 3);
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if (shadow_nodes <= max_nodes)
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return 0;
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return shadow_nodes - max_nodes;
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}
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static enum lru_status shadow_lru_isolate(struct list_head *item,
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struct list_lru_one *lru,
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spinlock_t *lru_lock,
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void *arg)
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{
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struct address_space *mapping;
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struct radix_tree_node *node;
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unsigned int i;
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int ret;
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/*
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* Page cache insertions and deletions synchroneously maintain
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* the shadow node LRU under the mapping->tree_lock and the
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* lru_lock. Because the page cache tree is emptied before
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* the inode can be destroyed, holding the lru_lock pins any
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* address_space that has radix tree nodes on the LRU.
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*
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* We can then safely transition to the mapping->tree_lock to
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* pin only the address_space of the particular node we want
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* to reclaim, take the node off-LRU, and drop the lru_lock.
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*/
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node = container_of(item, struct radix_tree_node, private_list);
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mapping = node->private_data;
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/* Coming from the list, invert the lock order */
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if (!spin_trylock(&mapping->tree_lock)) {
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spin_unlock(lru_lock);
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ret = LRU_RETRY;
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goto out;
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}
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list_lru_isolate(lru, item);
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spin_unlock(lru_lock);
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/*
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* The nodes should only contain one or more shadow entries,
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* no pages, so we expect to be able to remove them all and
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* delete and free the empty node afterwards.
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*/
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BUG_ON(!node->count);
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BUG_ON(node->count & RADIX_TREE_COUNT_MASK);
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for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {
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if (node->slots[i]) {
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BUG_ON(!radix_tree_exceptional_entry(node->slots[i]));
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node->slots[i] = NULL;
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BUG_ON(node->count < (1U << RADIX_TREE_COUNT_SHIFT));
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node->count -= 1U << RADIX_TREE_COUNT_SHIFT;
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BUG_ON(!mapping->nrexceptional);
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mapping->nrexceptional--;
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}
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}
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BUG_ON(node->count);
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inc_node_state(page_pgdat(virt_to_page(node)), WORKINGSET_NODERECLAIM);
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if (!__radix_tree_delete_node(&mapping->page_tree, node))
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BUG();
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spin_unlock(&mapping->tree_lock);
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ret = LRU_REMOVED_RETRY;
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out:
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local_irq_enable();
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cond_resched();
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local_irq_disable();
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spin_lock(lru_lock);
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return ret;
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}
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static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
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struct shrink_control *sc)
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{
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unsigned long ret;
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/* list_lru lock nests inside IRQ-safe mapping->tree_lock */
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local_irq_disable();
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ret = list_lru_shrink_walk(&workingset_shadow_nodes, sc,
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shadow_lru_isolate, NULL);
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local_irq_enable();
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return ret;
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}
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static struct shrinker workingset_shadow_shrinker = {
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.count_objects = count_shadow_nodes,
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.scan_objects = scan_shadow_nodes,
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.seeks = DEFAULT_SEEKS,
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.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
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};
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/*
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* Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
|
|
* mapping->tree_lock.
|
|
*/
|
|
static struct lock_class_key shadow_nodes_key;
|
|
|
|
static int __init workingset_init(void)
|
|
{
|
|
unsigned int timestamp_bits;
|
|
unsigned int max_order;
|
|
int ret;
|
|
|
|
BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
|
|
/*
|
|
* Calculate the eviction bucket size to cover the longest
|
|
* actionable refault distance, which is currently half of
|
|
* memory (totalram_pages/2). However, memory hotplug may add
|
|
* some more pages at runtime, so keep working with up to
|
|
* double the initial memory by using totalram_pages as-is.
|
|
*/
|
|
timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
|
|
max_order = fls_long(totalram_pages - 1);
|
|
if (max_order > timestamp_bits)
|
|
bucket_order = max_order - timestamp_bits;
|
|
pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
|
|
timestamp_bits, max_order, bucket_order);
|
|
|
|
ret = list_lru_init_key(&workingset_shadow_nodes, &shadow_nodes_key);
|
|
if (ret)
|
|
goto err;
|
|
ret = register_shrinker(&workingset_shadow_shrinker);
|
|
if (ret)
|
|
goto err_list_lru;
|
|
return 0;
|
|
err_list_lru:
|
|
list_lru_destroy(&workingset_shadow_nodes);
|
|
err:
|
|
return ret;
|
|
}
|
|
module_init(workingset_init);
|