linux-kernel - Re: [PATCH 6/6] writeback: refill b

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Date:	Thu, 5 May 2011 18:37:08 +0200
From:	Jan Kara <jack@...e.cz>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mel@...ux.vnet.ibm.com>,
	Mel Gorman <mel@....ul.ie>, Dave Chinner <david@...morbit.com>,
	Itaru Kitayama <kitayama@...bb4u.ne.jp>,
	Minchan Kim <minchan.kim@...il.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/6] writeback: refill b_io iff empty

On Wed 04-05-11 15:39:31, Wu Fengguang wrote:
> To help understand the behavior change, I wrote the writeback_queue_io
> trace event, and found very different patterns between
> - vanilla kernel
> - this patchset plus the sync livelock fixes
> 
> Basically the vanilla kernel each time pulls a random number of inodes
> from b_dirty, while the patched kernel tends to pull a fixed number of
> inodes (enqueue=1031) from b_dirty. The new behavior is very interesting...
  This regularity is really strange. Did you have a chance to look more into
it? I find it highly unlikely that there would be exactly 1031 dirty inodes
in b_dirty list every time you call move_expired_inodes()...

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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