linux-kernel - Re: [PATCH] writeback: Per-block device bdi->dirty_writeback_interval and bdi->dirty_expire

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Date:	Fri, 19 Aug 2011 14:55:43 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Kautuk Consul <consul.kautuk@...il.com>,
	Mel Gorman <mgorman@...e.de>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
	Greg Thelen <gthelen@...gle.com>
Subject: Re: [PATCH] writeback: Per-block device
 bdi->dirty_writeback_interval and bdi->dirty_expire_interval.

On Thu, 2011-08-18 at 21:13 +0800, Wu Fengguang wrote:
> Thinking twice about it, I find that the different requirements for
> interval flash/external microSD can also be solved by this scheme.
> 
> Introduce a per-bdi dirty_background_time (and optionally dirty_time)
> as the counterpart of (and works in parallel to) global dirty[_background]_ratio,
> however with unit "milliseconds worth of data".
> 
> The per-bdi dirty_background_time will be set low for external microSD
> and high for internal flash. Then you get timely writeouts for microSD
> and reasonably delayed writes for internal flash (controllable by the
> global dirty_expire_centisecs).
> 
> The dirty_background_time will actually work more reliable than
> dirty_expire_centisecs because it will checked immediately after the
> application dirties more pages. And the dirty_time could provide
> strong data integrity guarantee -- much stronger than
> dirty_expire_centisecs -- if used.
> 
> Does that sound reasonable?

Yes, this would probably work. But note, we do not have this problem
anymore, I was just talking about the past experience, so I cannot
validate any possible patch.

Thanks.

-- 
Best Regards,
Artem Bityutskiy

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