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Subject: Re: [PATCH] doc: cgroup: update note about conditions when oom killer
 is invoked
To:     Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     cgroups@vger.kernel.org, Roman Gushchin <guro@fb.com>,
        Michal Hocko <mhocko@suse.com>
References: <158894738928.208854.5244393925922074518.stgit@buzz>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <b0242e17-c436-747a-8403-d263a16553d0@infradead.org>
Date:   Fri, 8 May 2020 09:00:15 -0700
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Hi,

On 5/8/20 7:16 AM, 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>
> ---
>  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

	                                         allocations

> +	succeed unless OOM killer choose current task as a victim.

	                          chooses

> +
> +	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.
> +
>  	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
> 


thanks for updating the docs.
-- 
~Randy