linux-kernel - Re: [PATCH] mm: memcontrol: do not recurse in direct reclaim

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Date:   Tue, 25 Oct 2016 17:07:59 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Tejun Heo <tj@...nel.org>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH] mm: memcontrol: do not recurse in direct reclaim

On Tue 25-10-16 11:01:42, Johannes Weiner wrote:
> On Tue, Oct 25, 2016 at 04:45:44PM +0200, Michal Hocko wrote:
> > On Tue 25-10-16 10:10:50, Johannes Weiner wrote:
> > > Like other direct reclaimers, mark tasks in memcg reclaim PF_MEMALLOC
> > > to avoid recursing into any other form of direct reclaim. Then let
> > > recursive charges from PF_MEMALLOC contexts bypass the cgroup limit.
> > 
> > Should we mark this for stable (up to 4.5) which changed the out-out to
> > opt-in?
> 
> Yes, good point.
> 
> Internally, we're pulling it into our 4.6 tree as well. The commit
> that fixes the particular bug we encountered in btrfs is a9bb7e620efd
> ("memcg: only account kmem allocations marked as __GFP_ACCOUNT") in
> 4.5+, so you could argue that we don't need the backport in kernels
> with this commit. And I'm not aware of other manifestations of this
> problem. But the unbounded recursion hole is still there, technically,
> so we might just want to put it into all stable kernels and be safe.
> 
> So either
> 
> Cc: <stable@...r.kernel.org>	# up to and including 4.5

As the patch was released in 4.5 it shouldn't be needed in 4.5 stable
tree but

> or, and I'm leaning toward that, simply
> 
> Cc: <stable@...r.kernel.org>

this sounds less confusing I guess.

-- 
Michal Hocko
SUSE Labs