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Date:   Thu, 18 Feb 2021 12:39:09 +0000
From:   Chris Down <chris@chrisdown.name>
To:     Eiichi Tsukata <eiichi.tsukata@nutanix.com>
Cc:     Michal Hocko <mhocko@suse.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        "corbet@lwn.net" <corbet@lwn.net>,
        "mcgrof@kernel.org" <mcgrof@kernel.org>,
        "keescook@chromium.org" <keescook@chromium.org>,
        "yzaikin@google.com" <yzaikin@google.com>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        Felipe Franciosi <felipe@nutanix.com>,
        "shakeelb@google.com" <shakeelb@google.com>
Subject: Re: [RFC PATCH] mm, oom: introduce vm.sacrifice_hugepage_on_oom
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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.