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![Roman Gushchin](/assets/img/avatar_default.png)
Memcg counters for shadow nodes are broken because the memcg pointer is obtained in a wrong way. The following approach is used: virt_to_page(xa_node)->mem_cgroup Since commit4d96ba3530
("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages") page->mem_cgroup pointer isn't set for slab pages, so memcg_from_slab_page() should be used instead. Also I doubt that it ever worked correctly: virt_to_head_page() should be used instead of virt_to_page(). Otherwise objects residing on tail pages are not accounted, because only the head page contains a valid mem_cgroup pointer. That was a case since the introduction of these counters by the commit68d48e6a2d
("mm: workingset: add vmstat counter for shadow nodes"). Link: http://lkml.kernel.org/r/20190801233532.138743-1-guro@fb.com Fixes:4d96ba3530
("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages") Signed-off-by: Roman Gushchin <guro@fb.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Michal Hocko <mhocko@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
571 lines
19 KiB
C
571 lines
19 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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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/shmem_fs.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/dax.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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* Refaulting inactive 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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* That means if inactive cache is refaulting with a suitable refault
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* distance, we assume the cache workingset is transitioning and put
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* pressure on the current active list.
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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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* Refaulting active pages
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*
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* If on the other hand the refaulting pages have recently been
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* deactivated, it means that the active list is no longer protecting
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* actively used cache from reclaim. The cache is NOT transitioning to
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* a different workingset; the existing workingset is thrashing in the
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* space allocated to the page 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
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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 ((BITS_PER_LONG - BITS_PER_XA_VALUE) + \
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1 + NODES_SHIFT + 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 xarray
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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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bool workingset)
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{
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eviction >>= bucket_order;
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eviction &= EVICTION_MASK;
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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 << 1) | workingset;
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return xa_mk_value(eviction);
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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, bool *workingsetp)
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{
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unsigned long entry = xa_to_value(shadow);
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int memcgid, nid;
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bool workingset;
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workingset = entry & 1;
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entry >>= 1;
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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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*workingsetp = workingset;
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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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* @page: the page being evicted
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*
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* Returns a shadow entry to be stored in @page->mapping->i_pages 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 page *page)
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{
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struct pglist_data *pgdat = page_pgdat(page);
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struct mem_cgroup *memcg = page_memcg(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, PageWorkingset(page));
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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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* @page: the freshly allocated replacement 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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void workingset_refault(struct page *page, void *shadow)
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{
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unsigned long refault_distance;
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struct pglist_data *pgdat;
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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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bool workingset;
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int memcgid;
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unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
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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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goto out;
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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, MAX_NR_ZONES);
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/*
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* Calculate the refault distance
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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. There is a
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* special case: usually, shadow entries have a short lifetime
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* and are either refaulted or reclaimed along with the inode
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* before they get too old. But it is not impossible for the
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* inactive_age to lap a shadow entry in the field, which can
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* then result in a false small refault distance, leading to a
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* false activation should this old entry actually refault
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* again. However, earlier kernels used to deactivate
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* unconditionally with *every* reclaim invocation for the
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* longest time, so the occasional inappropriate activation
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* leading to pressure on the active list is not a problem.
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*/
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refault_distance = (refault - eviction) & EVICTION_MASK;
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inc_lruvec_state(lruvec, WORKINGSET_REFAULT);
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/*
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* Compare the distance to the existing workingset size. We
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* don't act on pages that couldn't stay resident even if all
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* the memory was available to the page cache.
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*/
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if (refault_distance > active_file)
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goto out;
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SetPageActive(page);
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atomic_long_inc(&lruvec->inactive_age);
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inc_lruvec_state(lruvec, WORKINGSET_ACTIVATE);
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/* Page was active prior to eviction */
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if (workingset) {
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SetPageWorkingset(page);
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inc_lruvec_state(lruvec, WORKINGSET_RESTORE);
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}
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out:
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rcu_read_unlock();
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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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static struct list_lru shadow_nodes;
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void workingset_update_node(struct xa_node *node)
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{
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/*
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* Track non-empty nodes that contain only shadow entries;
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* unlink those that contain pages or are being freed.
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*
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* Avoid acquiring the list_lru lock when the nodes are
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* already where they should be. The list_empty() test is safe
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* as node->private_list is protected by the i_pages lock.
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*/
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VM_WARN_ON_ONCE(!irqs_disabled()); /* For __inc_lruvec_page_state */
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if (node->count && node->count == node->nr_values) {
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if (list_empty(&node->private_list)) {
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list_lru_add(&shadow_nodes, &node->private_list);
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__inc_lruvec_slab_state(node, WORKINGSET_NODES);
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}
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} else {
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if (!list_empty(&node->private_list)) {
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list_lru_del(&shadow_nodes, &node->private_list);
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__dec_lruvec_slab_state(node, WORKINGSET_NODES);
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}
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}
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}
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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 max_nodes;
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unsigned long nodes;
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unsigned long pages;
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nodes = list_lru_shrink_count(&shadow_nodes, sc);
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/*
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* Approximate a reasonable limit for the nodes
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* containing shadow entries. We don't need to keep more
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* shadow entries than possible pages on the active list,
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* since refault distances bigger than that are dismissed.
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*
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* The size of the active list converges toward 100% of
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* overall page cache as memory grows, with only a tiny
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* inactive list. Assume the total cache size for that.
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*
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* Nodes might be sparsely populated, with only one shadow
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* entry in the extreme case. Obviously, we cannot keep one
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* node for every eligible shadow entry, so compromise on a
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* worst-case density of 1/8th. Below that, not all eligible
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* refaults can be detected anymore.
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*
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* On 64-bit with 7 xa_nodes per page and 64 slots
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* each, this will reclaim shadow entries when they consume
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* ~1.8% of available memory:
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*
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* PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
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*/
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#ifdef CONFIG_MEMCG
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if (sc->memcg) {
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struct lruvec *lruvec;
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int i;
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lruvec = mem_cgroup_lruvec(NODE_DATA(sc->nid), sc->memcg);
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for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
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pages += lruvec_page_state_local(lruvec,
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NR_LRU_BASE + i);
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pages += lruvec_page_state_local(lruvec, NR_SLAB_RECLAIMABLE);
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pages += lruvec_page_state_local(lruvec, NR_SLAB_UNRECLAIMABLE);
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} else
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#endif
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pages = node_present_pages(sc->nid);
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max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
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if (!nodes)
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return SHRINK_EMPTY;
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if (nodes <= max_nodes)
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return 0;
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return 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) __must_hold(lru_lock)
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{
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struct xa_node *node = container_of(item, struct xa_node, private_list);
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XA_STATE(xas, node->array, 0);
|
|
struct address_space *mapping;
|
|
int ret;
|
|
|
|
/*
|
|
* Page cache insertions and deletions synchroneously maintain
|
|
* the shadow node LRU under the i_pages lock and the
|
|
* lru_lock. Because the page cache tree is emptied before
|
|
* the inode can be destroyed, holding the lru_lock pins any
|
|
* address_space that has nodes on the LRU.
|
|
*
|
|
* We can then safely transition to the i_pages lock to
|
|
* pin only the address_space of the particular node we want
|
|
* to reclaim, take the node off-LRU, and drop the lru_lock.
|
|
*/
|
|
|
|
mapping = container_of(node->array, struct address_space, i_pages);
|
|
|
|
/* Coming from the list, invert the lock order */
|
|
if (!xa_trylock(&mapping->i_pages)) {
|
|
spin_unlock_irq(lru_lock);
|
|
ret = LRU_RETRY;
|
|
goto out;
|
|
}
|
|
|
|
list_lru_isolate(lru, item);
|
|
__dec_lruvec_slab_state(node, WORKINGSET_NODES);
|
|
|
|
spin_unlock(lru_lock);
|
|
|
|
/*
|
|
* The nodes should only contain one or more shadow entries,
|
|
* no pages, so we expect to be able to remove them all and
|
|
* delete and free the empty node afterwards.
|
|
*/
|
|
if (WARN_ON_ONCE(!node->nr_values))
|
|
goto out_invalid;
|
|
if (WARN_ON_ONCE(node->count != node->nr_values))
|
|
goto out_invalid;
|
|
mapping->nrexceptional -= node->nr_values;
|
|
xas.xa_node = xa_parent_locked(&mapping->i_pages, node);
|
|
xas.xa_offset = node->offset;
|
|
xas.xa_shift = node->shift + XA_CHUNK_SHIFT;
|
|
xas_set_update(&xas, workingset_update_node);
|
|
/*
|
|
* We could store a shadow entry here which was the minimum of the
|
|
* shadow entries we were tracking ...
|
|
*/
|
|
xas_store(&xas, NULL);
|
|
__inc_lruvec_slab_state(node, WORKINGSET_NODERECLAIM);
|
|
|
|
out_invalid:
|
|
xa_unlock_irq(&mapping->i_pages);
|
|
ret = LRU_REMOVED_RETRY;
|
|
out:
|
|
cond_resched();
|
|
spin_lock_irq(lru_lock);
|
|
return ret;
|
|
}
|
|
|
|
static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
|
|
struct shrink_control *sc)
|
|
{
|
|
/* list_lru lock nests inside the IRQ-safe i_pages lock */
|
|
return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
|
|
NULL);
|
|
}
|
|
|
|
static struct shrinker workingset_shadow_shrinker = {
|
|
.count_objects = count_shadow_nodes,
|
|
.scan_objects = scan_shadow_nodes,
|
|
.seeks = 0, /* ->count reports only fully expendable nodes */
|
|
.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
|
|
};
|
|
|
|
/*
|
|
* Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
|
|
* i_pages lock.
|
|
*/
|
|
static struct lock_class_key shadow_nodes_key;
|
|
|
|
static int __init workingset_init(void)
|
|
{
|
|
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 = prealloc_shrinker(&workingset_shadow_shrinker);
|
|
if (ret)
|
|
goto err;
|
|
ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
|
|
&workingset_shadow_shrinker);
|
|
if (ret)
|
|
goto err_list_lru;
|
|
register_shrinker_prepared(&workingset_shadow_shrinker);
|
|
return 0;
|
|
err_list_lru:
|
|
free_prealloced_shrinker(&workingset_shadow_shrinker);
|
|
err:
|
|
return ret;
|
|
}
|
|
module_init(workingset_init);
|