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 <khlebni...@yandex-team.ru>
Acked-by: Michal Hocko <mho...@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.
> +
> 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
--
Michal Hocko
SUSE Labs
