linux-kernel - Re: [PATCH] memcg: fix memory.high target

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Message-ID: <20151123161754.GA13000@cmpxchg.org>
Date:	Mon, 23 Nov 2015 11:17:54 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...nel.org>, Tejun Heo <tj@...nel.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memcg: fix memory.high target

On Mon, Nov 23, 2015 at 03:22:31PM +0300, Vladimir Davydov wrote:
> When the memory.high threshold is exceeded, try_charge() schedules a
> task_work to reclaim the excess. The reclaim target is set to the number
> of pages requested by try_charge(). This is wrong, because try_charge()
> usually charges more pages than requested (batch > nr_pages) in order to
> refill per cpu stocks. As a result, a process in a cgroup can easily
> exceed memory.high significantly when doing a lot of charges w/o
> returning to userspace (e.g. reading a file in big chunks).
> 
> Fix this issue by assuring that when exceeding memory.high a process
> reclaims as many pages as were actually charged (i.e. batch).
> 
> Signed-off-by: Vladimir Davydov <vdavydov@...tuozzo.com>

Acked-by: Johannes Weiner <hannes@...xchg.org>
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