From: Roman Gushchin guro@fb.com
mainline inclusion from mainline-v5.3-rc7 commit bee07b33db78d4ee7ed6a2fe810b9473d5471fe4 category: bugfix bugzilla: 34611 CVE: NA
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I've noticed that the "slab" value in memory.stat is sometimes 0, even if some children memory cgroups have a non-zero "slab" value. The following investigation showed that this is the result of the kmem_cache reparenting in combination with the per-cpu batching of slab vmstats.
At the offlining some vmstat value may leave in the percpu cache, not being propagated upwards by the cgroup hierarchy. It means that stats on ancestor levels are lower than actual. Later when slab pages are released, the precise number of pages is substracted on the parent level, making the value negative. We don't show negative values, 0 is printed instead.
To fix this issue, let's flush percpu slab memcg and lruvec stats on memcg offlining. This guarantees that numbers on all ancestor levels are accurate and match the actual number of outstanding slab pages.
Link: http://lkml.kernel.org/r/20190819202338.363363-3-guro@fb.com Fixes: fb2f2b0adb98 ("mm: memcg/slab: reparent memcg kmem_caches on cgroup removal") Signed-off-by: Roman Gushchin guro@fb.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Michal Hocko mhocko@kernel.org Cc: Vladimir Davydov vdavydov.dev@gmail.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Chen Zhou chenzhou10@huawei.com Signed-off-by: Liu Shixin liushixin2@huawei.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- include/linux/mmzone.h | 5 +++-- mm/memcontrol.c | 35 +++++++++++++++++++++++++++-------- 2 files changed, 30 insertions(+), 10 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 8c546c5b0f21..c9a826979e8b 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -158,8 +158,9 @@ enum node_stat_item { NR_INACTIVE_FILE, /* " " " " " */ NR_ACTIVE_FILE, /* " " " " " */ NR_UNEVICTABLE, /* " " " " " */ - NR_SLAB_RECLAIMABLE, - NR_SLAB_UNRECLAIMABLE, + NR_SLAB_RECLAIMABLE, /* Please do not reorder this item */ + NR_SLAB_UNRECLAIMABLE, /* and this one without looking at + * memcg_flush_percpu_vmstats() first. */ NR_ISOLATED_ANON, /* Temporary isolated pages from anon lru */ NR_ISOLATED_FILE, /* Temporary isolated pages from file lru */ WORKINGSET_REFAULT, diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 5a2da8787f36..42dd131581b8 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3263,37 +3263,49 @@ static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css, } }
-static void memcg_flush_percpu_vmstats(struct mem_cgroup *memcg) +static void memcg_flush_percpu_vmstats(struct mem_cgroup *memcg, bool slab_only) { unsigned long stat[MEMCG_NR_STAT]; struct mem_cgroup *mi; int node, cpu, i; + int min_idx, max_idx;
- for (i = 0; i < MEMCG_NR_STAT; i++) + if (slab_only) { + min_idx = NR_SLAB_RECLAIMABLE; + max_idx = NR_SLAB_UNRECLAIMABLE; + } else { + min_idx = 0; + max_idx = MEMCG_NR_STAT; + } + + for (i = min_idx; i < max_idx; i++) stat[i] = 0;
for_each_online_cpu(cpu) - for (i = 0; i < MEMCG_NR_STAT; i++) + for (i = min_idx; i < max_idx; i++) stat[i] += raw_cpu_read(memcg->vmstats_percpu->stat[i]);
for (mi = memcg; mi; mi = parent_mem_cgroup(mi)) - for (i = 0; i < MEMCG_NR_STAT; i++) + for (i = min_idx; i < max_idx; i++) atomic_long_add(stat[i], &mi->vmstats[i]);
+ if (!slab_only) + max_idx = NR_VM_NODE_STAT_ITEMS; + for_each_node(node) { struct mem_cgroup_per_node *pn = memcg->nodeinfo[node]; struct mem_cgroup_per_node *pi;
- for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) + for (i = min_idx; i < max_idx; i++) stat[i] = 0;
for_each_online_cpu(cpu) - for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) + for (i = min_idx; i < max_idx; i++) stat[i] += raw_cpu_read( pn->lruvec_stat_cpu->count[i]);
for (pi = pn; pi; pi = parent_nodeinfo(pi, node)) - for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) + for (i = min_idx; i < max_idx; i++) atomic_long_add(stat[i], &pi->lruvec_stat[i]); } } @@ -3366,7 +3378,14 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg) if (!parent) parent = root_mem_cgroup;
+ /* + * Deactivate and reparent kmem_caches. Then flush percpu + * slab statistics to have precise values at the parent and + * all ancestor levels. It's required to keep slab stats + * accurate after the reparenting of kmem_caches. + */ memcg_deactivate_kmem_caches(memcg, parent); + memcg_flush_percpu_vmstats(memcg, true);
kmemcg_id = memcg->kmemcg_id; BUG_ON(kmemcg_id < 0); @@ -4734,7 +4753,7 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg) * Flush percpu vmstats and vmevents to guarantee the value correctness * on parent's and all ancestor levels. */ - memcg_flush_percpu_vmstats(memcg); + memcg_flush_percpu_vmstats(memcg, false); memcg_flush_percpu_vmevents(memcg); for_each_node(node) free_mem_cgroup_per_node_info(memcg, node);