linux-kernel - Re: OOM: Better, but still there on 4.9

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Message-ID: <20161216221420.GF7645@dhcp22.suse.cz>
Date:   Fri, 16 Dec 2016 23:14:20 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Chris Mason <clm@...com>
Cc:     Nils Holland <nholland@...ys.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, David Sterba <dsterba@...e.cz>,
        linux-btrfs@...r.kernel.org
Subject: Re: OOM: Better, but still there on 4.9

On Fri 16-12-16 13:15:18, Chris Mason wrote:
> On 12/16/2016 02:39 AM, Michal Hocko wrote:
[...]
> > I believe the right way to go around this is to pursue what I've started
> > in [1]. I will try to prepare something for testing today for you. Stay
> > tuned. But I would be really happy if somebody from the btrfs camp could
> > check the NOFS aspect of this allocation. We have already seen
> > allocation stalls from this path quite recently
> 
> Just double checking, are you asking why we're using GFP_NOFS to avoid going
> into btrfs from the btrfs writepages call, or are you asking why we aren't
> allowing highmem?

I am more interested in the NOFS part. Why cannot this be a full
GFP_KERNEL context? What kind of locks we would lock up when recursing
to the fs via slab shrinkers?
-- 
Michal Hocko
SUSE Labs