linux-kernel - Re: [PATCH 0/6] writeback time order/delay fixes take 3

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Message-ID: <20070824135504.GA9029@mail.ustc.edu.cn>
Date:	Fri, 24 Aug 2007 21:55:04 +0800
From:	Fengguang Wu <wfg@...l.ustc.edu.cn>
To:	David Chinner <dgc@....com>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Andrew Morton <akpm@...l.org>, Ken Chen <kenchen@...gle.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH 0/6] writeback time order/delay fixes take 3

On Thu, Aug 23, 2007 at 12:33:06PM +1000, David Chinner wrote:
> On Wed, Aug 22, 2007 at 09:18:41AM +0800, Fengguang Wu wrote:
> > On Tue, Aug 21, 2007 at 08:23:14PM -0400, Chris Mason wrote:
> > Notes:
> > (1) I'm not sure inode number is correlated to disk location in
> >     filesystems other than ext2/3/4. Or parent dir?
> 
> The correspond to the exact location on disk on XFS. But, XFS has it's
> own inode clustering (see xfs_iflush) and it can't be moved up
> into the generic layers because of locking and integration into
> the transaction subsystem.
>
> > (2) It duplicates some function of elevators. Why is it necessary?
> 
> The elevators have no clue as to how the filesystem might treat adjacent
> inodes. In XFS, inode clustering is a fundamental feature of the inode
> reading and writing and that is something no elevator can hope to
> acheive....
 
Thank you. That explains the linear write curve(perfect!) in Chris' graph.

I wonder if XFS can benefit any more from the general writeback clustering.
How large would be a typical XFS cluster?

-fengguang

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