linux-kernel - Re: [patch 01/10] mm: memcg: fix compaction/migration failing due to memcg limits

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Date:	Thu, 12 Jul 2012 11:12:27 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	Wanpeng Li <liwp.linux@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 01/10] mm: memcg: fix compaction/migration failing due to
 memcg limits

On Thu, Jul 12, 2012 at 04:54:07PM +0800, Wanpeng Li wrote:
> On Wed, Jul 11, 2012 at 07:02:13PM +0200, Johannes Weiner wrote:
> >Compaction (and page migration in general) can currently be hindered
> >through pages being owned by memory cgroups that are at their limits
> >and unreclaimable.
> >
> >The reason is that the replacement page is being charged against the
> >limit while the page being replaced is also still charged.  But this
> >seems unnecessary, given that only one of the two pages will still be
> >in use after migration finishes.
> >
> >This patch changes the memcg migration sequence so that the
> >replacement page is not charged.  Whatever page is still in use after
> >successful or failed migration gets to keep the charge of the page
> >that was going to be replaced.
> >
> >The replacement page will still show up temporarily in the rss/cache
> >statistics, this can be fixed in a later patch as it's less urgent.
> 
> So I want to know after this patch be merged if mem_cgroup_wait_acct_move
> still make sense, if the answer is no, I will send a patch to remove it.

This change is about migrating a charge from one physical page to
another, account moving is about migrating charges between groups.
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