linux-kernel - Re: [PATCH v3 3/6] memcg: Simplify mem_cgroup_force_empty

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Date:	Wed, 14 Nov 2012 13:33:30 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Glauber Costa <glommer@...allels.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <bsingharora@...il.com>
Subject: Re: [PATCH v3 3/6] memcg: Simplify mem_cgroup_force_empty_list error
 handling

On Wed, Nov 14, 2012 at 02:59:30PM +0100, Michal Hocko wrote:
> On Tue 13-11-12 16:10:41, Johannes Weiner wrote:
> > Would it make sense to stick a wait_on_page_locked() in there just so
> > that we don't busy spin on a page under migration/reclaim?
> 
> Hmm, this would also mean that get_page_unless_zero would fail as well
> and so we would schedule in mem_cgroup_force_empty_list. It is true that
> there might be no other runnable task so we can busy loop so yes this
> would help. Care to cook the patch?

Eventually get_page_unless_zero() would fail but we could still spin
on a page while it's off the LRU and migration performs writeback on
it e.g.  cond_resched() does not necessarily schedule just because
there is another runnable task, I think, it's voluntary preemption
when the task needs rescheduling anyway, not yield.

Maybe not worth bothering...
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