linux-kernel - Re: [BUGFIX][PATCH 5/5] memcg: fix percpu cached charge draining frequency

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Date:	Mon, 13 Jun 2011 14:25:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"bsingharora@...il.com" <bsingharora@...il.com>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>, Ying Han <yinghan@...gle.com>
Subject: Re: [BUGFIX][PATCH 5/5] memcg: fix percpu cached charge draining
 frequency

On Mon, 13 Jun 2011 12:16:48 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> >From 18b12e53f1cdf6d7feed1f9226c189c34866338c Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Date: Mon, 13 Jun 2011 11:25:43 +0900
> Subject: [PATCH 5/5] memcg: fix percpu cached charge draining frequency
> 
>  For performance, memory cgroup caches some "charge" from res_counter
>  into per cpu cache. This works well but because it's cache,
>  it needs to be flushed in some cases. Typical cases are
>          1. when someone hit limit.
>          2. when rmdir() is called and need to charges to be 0.
> 
> But "1" has problem.
> 
> Recently, with large SMP machines, we see many kworker runs because
> of flushing memcg's cache. Bad things in implementation are
> that even if a cpu contains a cache for memcg not related to
> a memcg which hits limit, drain code is called.
> 
> This patch does
> 	A) check percpu cache contains a useful data or not.
> 	B) check other asynchronous percpu draining doesn't run.
> 	C) don't call local cpu callback.
> 	D) don't call at softlimit reclaim.
> 
>
> ...
>
> +DEFINE_MUTEX(percpu_charge_mutex);

I made this static.  If we later wish to give it kernel-wide scope then
"percpu_charge_mutex" will not be a good choice of name.

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