Re: [v5 4/4] mm, oom, docs: describe the cgroup-aware OOM killer
From: David Rientjes <rientjes@google.com>
Date: 2017-08-14 22:52:32
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On Mon, 14 Aug 2017, Roman Gushchin wrote:
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diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt index dec5afdaa36d..22108f31e09d 100644 --- a/Documentation/cgroup-v2.txt +++ b/Documentation/cgroup-v2.txt@@ -48,6 +48,7 @@ v1 is available under Documentation/cgroup-v1/. 5-2-1. Memory Interface Files 5-2-2. Usage Guidelines 5-2-3. Memory Ownership + 5-2-4. Cgroup-aware OOM Killer
Random curiousness, why cgroup-aware oom killer and not memcg-aware oom killer?
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5-3. IO 5-3-1. IO Interface Files 5-3-2. Writeback@@ -1002,6 +1003,37 @@ PAGE_SIZE multiple when read back. high limit is used and monitored properly, this limit's utility is limited to providing the final safety net. + memory.oom_kill_all_tasks + + A read-write single value file which exits on non-root
s/exits/exists/
+ cgroups. The default is "0". + + Defines whether the OOM killer should treat the cgroup + as a single entity during the victim selection.
Isn't this true independent of the memory.oom_kill_all_tasks setting? The cgroup aware oom killer will consider memcg's as logical units when deciding what to kill with or without memory.oom_kill_all_tasks, right? I think you cover this fact in the cgroup aware oom killer section below so this might result in confusion if described alongside a setting of memory.oom_kill_all_tasks.
+ + If set, OOM killer will kill all belonging tasks in + corresponding cgroup is selected as an OOM victim.
Maybe "If set, the OOM killer will kill all threads attached to the memcg if selected as an OOM victim." is better?
+ + Be default, OOM killer respect /proc/pid/oom_score_adj value + -1000, and will never kill the task, unless oom_kill_all_tasks + is set. + + memory.oom_priority + + A read-write single value file which exits on non-root
s/exits/exists/
+ cgroups. The default is "0". + + An integer number within the [-10000, 10000] range, + which defines the order in which the OOM killer selects victim + memory cgroups. + + OOM killer prefers memory cgroups with larger priority if they + are populated with elegible tasks.
s/elegible/eligible/
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+ + The oom_priority value is compared within sibling cgroups. + + The root cgroup has the oom_priority 0, which cannot be changed. + memory.events A read-only flat-keyed file which exists on non-root cgroups. The following entries are defined. Unless specified@@ -1206,6 +1238,36 @@ POSIX_FADV_DONTNEED to relinquish the ownership of memory areas belonging to the affected files to ensure correct memory ownership. +Cgroup-aware OOM Killer +~~~~~~~~~~~~~~~~~~~~~~~ + +Cgroup v2 memory controller implements a cgroup-aware OOM killer. +It means that it treats memory cgroups as first class OOM entities. + +Under OOM conditions the memory controller tries to make the best +choise of a victim, hierarchically looking for the largest memory +consumer. By default, it will look for the biggest task in the +biggest leaf cgroup. + +Be default, all cgroups have oom_priority 0, and OOM killer will +chose the largest cgroup recursively on each level. For non-root +cgroups it's possible to change the oom_priority, and it will cause +the OOM killer to look athe the priority value first, and compare +sizes only of cgroups with equal priority.
Maybe some description of "largest" would be helpful here? I think you could briefly describe what is accounted for in the decisionmaking. s/athe/at the/ Reading through this, it makes me wonder if doing s/cgroup/memcg/ over most of it would be better.
+ +But a user can change this behavior by enabling the per-cgroup +oom_kill_all_tasks option. If set, it causes the OOM killer treat +the whole cgroup as an indivisible memory consumer. In case if it's +selected as on OOM victim, all belonging tasks will be killed. + +Tasks in the root cgroup are treated as independent memory consumers, +and are compared with other memory consumers (e.g. leaf cgroups). +The root cgroup doesn't support the oom_kill_all_tasks feature. + +This affects both system- and cgroup-wide OOMs. For a cgroup-wide OOM +the memory controller considers only cgroups belonging to the sub-tree +of the OOM'ing cgroup. + IO --
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