Message-ID: <387963704.05674@ustc.edu.cn>
Date: Fri, 24 Aug 2007 21:55:04 +0800
From: Fengguang Wu <wfg@mail.ustc.edu.cn>
To: David Chinner <dgc@sgi.com>
Cc: Chris Mason <chris.mason@oracle.com>, Andrew Morton <akpm@osdl.org>,
       Ken Chen <kenchen@google.com>, linux-kernel@vger.kernel.org,
       linux-fsdevel@vger.kernel.org, Jens Axboe <jens.axboe@oracle.com>
Subject: Re: [PATCH 0/6] writeback time order/delay fixes take 3
Message-ID: <20070824135504.GA9029@mail.ustc.edu.cn>
References: <386910467.21100@ustc.edu.cn> <20070821202314.335e86ec@think.oraclecorp.com> <20070822011841.GA8090@mail.ustc.edu.cn> <20070823023306.GM61154114@sgi.com>
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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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