Messages in this thread | | | Subject | Re: [PATCH] doc: cgroup: update note about conditions when oom killer is invoked | From | Konstantin Khlebnikov <> | Date | Mon, 11 May 2020 12:34:00 +0300 |
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On 11/05/2020 11.39, Michal Hocko wrote: > On Fri 08-05-20 17:16:29, Konstantin Khlebnikov wrote: >> Starting from v4.19 commit 29ef680ae7c2 ("memcg, oom: move out_of_memory >> back to the charge path") cgroup oom killer is no longer invoked only from >> page faults. Now it implements the same semantics as global OOM killer: >> allocation context invokes OOM killer and keeps retrying until success. >> >> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> > > Acked-by: Michal Hocko <mhocko@suse.com> > >> --- >> Documentation/admin-guide/cgroup-v2.rst | 17 ++++++++--------- >> 1 file changed, 8 insertions(+), 9 deletions(-) >> >> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst >> index bcc80269bb6a..1bb9a8f6ebe1 100644 >> --- a/Documentation/admin-guide/cgroup-v2.rst >> +++ b/Documentation/admin-guide/cgroup-v2.rst >> @@ -1172,6 +1172,13 @@ PAGE_SIZE multiple when read back. >> Under certain circumstances, the usage may go over the limit >> temporarily. >> >> + In default configuration regular 0-order allocation always >> + succeed unless OOM killer choose current task as a victim. >> + >> + Some kinds of allocations don't invoke the OOM killer. >> + Caller could retry them differently, return into userspace >> + as -ENOMEM or silently ignore in cases like disk readahead. > > I would probably add -EFAULT but the less error codes we document the > better.
Yeah, EFAULT was a most obscure result of memory shortage. Fortunately with new behaviour this shouldn't happens a lot.
Actually where it is still possible? THP always fallback to 0-order. I mean EFAULT could appear inside kernel only if task is killed so nobody would see it.
> >> + >> This is the ultimate protection mechanism. As long as the >> high limit is used and monitored properly, this limit's >> utility is limited to providing the final safety net. >> @@ -1228,17 +1235,9 @@ PAGE_SIZE multiple when read back. >> The number of time the cgroup's memory usage was >> reached the limit and allocation was about to fail. >> >> - Depending on context result could be invocation of OOM >> - killer and retrying allocation or failing allocation. >> - >> - Failed allocation in its turn could be returned into >> - userspace as -ENOMEM or silently ignored in cases like >> - disk readahead. For now OOM in memory cgroup kills >> - tasks iff shortage has happened inside page fault. >> - >> This event is not raised if the OOM killer is not >> considered as an option, e.g. for failed high-order >> - allocations. >> + allocations or if caller asked to not retry attempts. >> >> oom_kill >> The number of processes belonging to this cgroup >
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