linux-kernel - Re: [PATCH v4 11/11] memcg: check memcg dirty limits in page writeback

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Message-ID: <xr93eib9nfue.fsf@ninji.mtv.corp.google.com>
Date:	Fri, 29 Oct 2010 09:06:33 -0700
From:	Greg Thelen <gthelen@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	containers@...ts.osdl.org, Andrea Righi <arighi@...eler.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Minchan Kim <minchan.kim@...il.com>,
	Ciju Rajan K <ciju@...ux.vnet.ibm.com>,
	David Rientjes <rientjes@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [PATCH v4 11/11] memcg: check memcg dirty limits in page writeback

KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> writes:

> On Fri, 29 Oct 2010 00:09:14 -0700
> Greg Thelen <gthelen@...gle.com> wrote:
>
>> If the current process is in a non-root memcg, then
>> balance_dirty_pages() will consider the memcg dirty limits
>> as well as the system-wide limits.  This allows different
>> cgroups to have distinct dirty limits which trigger direct
>> and background writeback at different levels.
>> 
>> Signed-off-by: Andrea Righi <arighi@...eler.com>
>> Signed-off-by: Greg Thelen <gthelen@...gle.com>
>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> Ideally, I think some comments in the code for "why we need double-check system's
> dirty limit and memcg's dirty limit" will be appreciated.

I will add to the balance_dirty_pages() comment.  It will read:
/*
 * balance_dirty_pages() must be called by processes which are generating dirty
 * data.  It looks at the number of dirty pages in the machine and will force
 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
 * If we're over `background_thresh' then the writeback threads are woken to
 * perform some writeout.  The current task may have per-memcg dirty
 * limits, which are also checked.
 */
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