linux-kernel - Re: [patch] Converting writeback linked lists to a tree based data structure

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Message-ID: <20080116075538.GW155407@sgi.com>
Date:	Wed, 16 Jan 2008 18:55:38 +1100
From:	David Chinner <dgc@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Fengguang Wu <wfg@...l.ustc.edu.cn>,
	Michael Rubin <mrubin@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch] Converting writeback linked lists to a tree based data structure

On Tue, Jan 15, 2008 at 07:44:15PM -0800, Andrew Morton wrote:
> On Wed, 16 Jan 2008 11:01:08 +0800 Fengguang Wu <wfg@...l.ustc.edu.cn> wrote:
> 
> > On Tue, Jan 15, 2008 at 09:53:42AM -0800, Michael Rubin wrote:
> > > On Jan 15, 2008 12:46 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > > > Just a quick question, how does this interact/depend-uppon etc.. with
> > > > Fengguangs patches I still have in my mailbox? (Those from Dec 28th)
> > > 
> > > They don't. They apply to a 2.6.24rc7 tree. This is a candidte for 2.6.25.
> > > 
> > > This work was done before Fengguang's patches. I am trying to test
> > > Fengguang's for comparison but am having problems with getting mm1 to
> > > boot on my systems.
> > 
> > Yeah, they are independent ones. The initial motivation is to fix the
> > bug "sluggish writeback on small+large files". Michael introduced
> > a new rbtree, and me introduced a new list(s_more_io_wait).
> > 
> > Basically I think rbtree is an overkill to do time based ordering.
> > Sorry, Michael. But s_dirty would be enough for that. Plus, s_more_io
> > provides fair queuing between small/large files, and s_more_io_wait
> > provides waiting mechanism for blocked inodes.
> > 
> > The time ordered rbtree may delay io for a blocked inode simply by
> > modifying its dirtied_when and reinsert it. But it would no longer be
> > that easy if it is to be ordered by location.
> 
> What does the term "ordered by location" mean?  Attemting to sort inodes by
> physical disk address?  By using their i_ino as a key?
> 
> That sounds optimistic.

In XFS, inode number is an encoding of it's location on disk, so
ordering inode writeback by inode number *does* make sense.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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