linux-kernel - Re: [RFC PATCH] mm, oom: introduce vm.sacrifice_hugepage_on

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Date:   Thu, 18 Feb 2021 12:39:09 +0000
From:   Chris Down <chris@...isdown.name>
To:     Eiichi Tsukata <eiichi.tsukata@...anix.com>
Cc:     Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "corbet@....net" <corbet@....net>,
        "mcgrof@...nel.org" <mcgrof@...nel.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "yzaikin@...gle.com" <yzaikin@...gle.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Felipe Franciosi <felipe@...anix.com>,
        "shakeelb@...gle.com" <shakeelb@...gle.com>
Subject: Re: [RFC PATCH] mm, oom: introduce vm.sacrifice_hugepage_on_oom

Eiichi Tsukata writes:
>>> But that comes with a challenge: despite listening on cgroup for
>>> pressure notifications (which happen from those runtime events we do
>>> not control),
>>
>> We do also have global pressure (PSI) counters. Have you tried to look
>> into those and try to back off even when the situation becomes critical?
>
>Yes. PSI counters help us to some extent. But we've found that in some cases
>OOM can happen before we observe memory pressure if memory bloat occurred
>rapidly. The proposed failsafe mechanism can cover even such a situation.
>Also, as I mentioned in commit message, oom notifiers doesn't work if OOM
>is triggered by memory allocation for kernel.

Hmm, do you have free swap? Without it, we can trivially go from fine to OOM in 
a totally binary fashion. As long as there's some swap space available, there 
should be a clear period where pressure is rising prior to OOM.