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Date:   Sat, 2 Nov 2019 17:28:21 +0100
From:   Damian Tometzki <damian.tometzki@familie-tometzki.de>
To:     Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc:     linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH] mm/memcontrol: update documentation about invoking oom
 killer
Message-ID: <20191102162821.GB19103@freebsd.familie-tometzki.de>
Mail-Followup-To: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        Michal Hocko <mhocko@suse.com>
References: <157270779336.1961.6528158720593572480.stgit@buzz>
 <20191102160252.GA19103@freebsd.familie-tometzki.de>
 <5c85a690-4ed7-91bb-30b5-c40174534a27@yandex-team.ru>
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On Sat, 02. Nov 19:14, Konstantin Khlebnikov wrote:
> 
> 
> On 02/11/2019 19.02, Damian Tometzki wrote:
> > On Sat, 02. Nov 18:16, 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@yandex-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
> > Hello Konstantin,
> > 
> > iff --> if :-)
> > 
> 
> This "iff" is shortened "if and only if".
> https://en.wikipedia.org/wiki/If_and_only_if

good to know :-)

> 
> > Best regards
> > Damian
> > 
> > 
> >> +		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
> >>