linux-kernel - Re: [patch 1/3] mm: memcontrol: take a css reference for each charged page

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Message-ID: <20140922082402.GA18526@esperanza>
Date:	Mon, 22 Sep 2014 12:24:02 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	<linux-mm@...ck.org>, Michal Hocko <mhocko@...e.cz>,
	Greg Thelen <gthelen@...gle.com>, Tejun Heo <tj@...nel.org>,
	<cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [patch 1/3] mm: memcontrol: take a css reference for each
 charged page

On Sat, Sep 20, 2014 at 04:00:33PM -0400, Johannes Weiner wrote:
> Charges currently pin the css indirectly by playing tricks during
> css_offline(): user pages stall the offlining process until all of
> them have been reparented, whereas kmemcg acquires a keep-alive
> reference if outstanding kernel pages are detected at that point.
> 
> In preparation for removing all this complexity, make the pinning
> explicit and acquire a css references for every charged page.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Reviewed-by: Vladimir Davydov <vdavydov@...allels.com>

Nit: In __mem_cgroup_clear_mc, we have the following hunk:

>		for (i = 0; i < mc.moved_swap; i++)
>			css_put(&mc.from->css);

Now we can simplify it using css_put_many.

Thanks,
Vladimir
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