linux-kernel - Re: [PATCH] mm/memcontrol: update documentation about invoking oom killer

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Message-ID: <alpine.DEB.2.21.1911021654020.34229@chino.kir.corp.google.com>
Date:   Sat, 2 Nov 2019 16:55:37 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] mm/memcontrol: update documentation about invoking oom
 killer

On Sat, 2 Nov 2019, Konstantin Khlebnikov wrote:

> Since commit 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the
> charge path") memcg invokes oom killer not only for user page-faults.
> This means 0-order allocation will either succeed or task get killed.
> 
> Fixes: 8e675f7af507 ("mm/oom_kill: count global and memory cgroup oom kills")
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> ---
>  Documentation/admin-guide/cgroup-v2.rst |    9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 5361ebec3361..eb47815e137b 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1219,8 +1219,13 @@ PAGE_SIZE multiple when read back.
>  
>  		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.
> +		disk readahead.
> +
> +		Before 4.19 OOM in memory cgroup killed tasks iff
> +		shortage has happened inside page fault, random
> +		syscall may fail with ENOMEM or EFAULT. Since 4.19
> +		failed memory cgroup allocation invokes oom killer and
> +		keeps retrying until it succeeds.
>  
>  		This event is not raised if the OOM killer is not
>  		considered as an option, e.g. for failed high-order

The previous text is obviously incorrect for today's kernels, but I'm 
curious if we should be conflating the documentation here by describing 
the pre-4.19 behavior.  OOM killing no longer happens only on page fault 
so maybe better to document the exact behavior today and not attempt to 
describe differences with previous versions?