linux-kernel - Re: [PATCH] fs, mm: account filp and names caches to kmemcg

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Date:   Thu, 26 Oct 2017 09:49:58 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Greg Thelen <gthelen@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>, linux-fsdevel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs, mm: account filp and names caches to kmemcg

On Wed 25-10-17 15:49:21, Greg Thelen wrote:
> Johannes Weiner <hannes@...xchg.org> wrote:
> 
> > On Wed, Oct 25, 2017 at 09:00:57PM +0200, Michal Hocko wrote:
[...]
> >> So just to make it clear you would be OK with the retry on successful
> >> OOM killer invocation and force charge on oom failure, right?
> >
> > Yeah, that sounds reasonable to me.
> 
> Assuming we're talking about retrying within try_charge(), then there's
> a detail to iron out...
> 
> If there is a pending oom victim blocked on a lock held by try_charge() caller
> (the "#2 Locks" case), then I think repeated calls to out_of_memory() will
> return true until the victim either gets MMF_OOM_SKIP or disappears.

true. And oom_reaper guarantees that MMF_OOM_SKIP gets set in the finit
amount of time.

> So a force
> charge fallback might be a needed even with oom killer successful invocations.
> Or we'll need to teach out_of_memory() to return three values (e.g. NO_VICTIM,
> NEW_VICTIM, PENDING_VICTIM) and try_charge() can loop on NEW_VICTIM.

No we, really want to wait for the oom victim to do its job. The only
thing we should be worried about is when out_of_memory doesn't invoke
the reaper. There is only one case like that AFAIK - GFP_NOFS request. I
have to think about this case some more. We currently fail in that case
the request.

-- 
Michal Hocko
SUSE Labs