linux-kernel - Re: [PATCH 3/6] memcg: remove PCG_MOVE_LOCK flag from page

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Message-ID: <20120220085617.GC1677@cmpxchg.org>
Date:	Mon, 20 Feb 2012 09:56:17 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>,
	Greg Thelen <gthelen@...gle.com>, Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH 3/6] memcg: remove PCG_MOVE_LOCK flag from page_cgroup

On Fri, Feb 17, 2012 at 06:26:51PM +0900, KAMEZAWA Hiroyuki wrote:
> >From 62a96c625be0c30fc5828d88685b6873ed254060 Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Date: Thu, 2 Feb 2012 11:49:59 +0900
> Subject: [PATCH 3/6] memcg: remove PCG_MOVE_LOCK flag from page_cgroup.
> 
> PCG_MOVE_LOCK is used for bit spinlock to avoid race between overwriting
> pc->mem_cgroup and page statistics accounting per memcg.
> This lock helps to avoid the race but the race is very rare because moving
> tasks between cgroup is not a usual job.
> So, it seems using 1bit per page is too costly.
> 
> This patch changes this lock as per-memcg spinlock and removes PCG_MOVE_LOCK.
> 
> If smaller lock is required, we'll be able to add some hashes but
> I'd like to start from this.
> 
> Changelog:
>   - fixed to pass memcg as an argument rather than page_cgroup.
>     and renamed from move_lock_page_cgroup() to move_lock_mem_cgroup()
> 
> Acked-by: Greg Thelen <gthelen@...gle.com>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

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