linux-kernel - Re: [patch 4/5] mm: memcontrol: continue cache reclaim from offlined groups

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Date:	Thu, 16 Oct 2014 23:02:21 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vladimir Davydov <vdavydov@...allels.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 4/5] mm: memcontrol: continue cache reclaim from offlined
 groups

On Wed, Oct 15, 2014 at 05:25:55PM +0200, Michal Hocko wrote:
> On Tue 14-10-14 12:20:36, Johannes Weiner wrote:
> > On cgroup deletion, outstanding page cache charges are moved to the
> > parent group so that they're not lost and can be reclaimed during
> > pressure on/inside said parent.  But this reparenting is fairly tricky
> > and its synchroneous nature has led to several lock-ups in the past.
> > 
> > Since css iterators now also include offlined css, memcg iterators can
> > be changed to include offlined children during reclaim of a group, and
> > leftover cache can just stay put.
> 
> I think it would be nice to mention c2931b70a32c (cgroup: iterate
> cgroup_subsys_states directly) here to have a full context about the
> tryget vs tryget_online.

Yes, that commit is probably the most direct dependency.

Andrew, could you update the changelog in place to have that paragraph
read

Since c2931b70a32c ("cgroup: iterate cgroup_subsys_states directly")
css iterators now also include offlined css, so memcg iterators can be
changed to include offlined children during reclaim of a group, and
leftover cache can just stay put.

please?  Thanks!

> > There is a slight change of behavior in that charges of deleted groups
> > no longer show up as local charges in the parent.  But they are still
> > included in the parent's hierarchical statistics.
> 
> Thank you for pulling drain_stock cleanup out. This made the patch so
> much easier to review.
>  
> > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> 
> Acked-by: Michal Hocko <mhocko@...e.cz>

Thanks you!
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