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

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Date:   Wed, 17 Feb 2021 08:54:55 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Eiichi Tsukata <eiichi.tsukata@...anix.com>, corbet@....net,
        mike.kravetz@...cle.com, mcgrof@...nel.org, keescook@...omium.org,
        yzaikin@...gle.com, akpm@...ux-foundation.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        felipe.franciosi@...anix.com
Subject: Re: [RFC PATCH] mm, oom: introduce vm.sacrifice_hugepage_on_oom

On Tue 16-02-21 13:53:12, David Rientjes wrote:
> On Tue, 16 Feb 2021, Michal Hocko wrote:
[...]
> > Overall, I am not really happy about this feature even when above is
> > fixed, but let's hear more the actual problem first.
> 
> Shouldn't this behavior be possible as an oomd plugin instead, perhaps 
> triggered by psi?  I'm not sure if oomd is intended only to kill something 
> (oomkilld? lol) or if it can be made to do sysadmin level behavior, such 
> as shrinking the hugetlb pool, to solve the oom condition.

It should be under control of an admin who knows what the pool is
preallocated for and whether a decrease (e.g. a temporal one) is
tolerable.
 
> If so, it seems like we want to do this at the absolute last minute.  In 
> other words, reclaim has failed to free memory by other means so we would 
> like to shrink the hugetlb pool.  (It's the reason why it's implemented as 
> a predecessor to oom as opposed to part of reclaim in general.)
> 
> Do we have the ability to suppress the oom killer until oomd has a chance 
> to react in this scenario?

We don't and I do not think we want to bind the kernel oom behavior to
any userspace process. We have extensively discussed things like this in
the past IIRC.

-- 
Michal Hocko
SUSE Labs