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

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Date:	Wed, 16 Jan 2008 17:07:20 +0800
From:	Fengguang Wu <wfg@...l.ustc.edu.cn>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	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 09:51:49PM -0800, Andrew Morton wrote:
> On Wed, 16 Jan 2008 12:55:07 +0800 Fengguang Wu <wfg@...l.ustc.edu.cn> wrote:
> 
> > On Tue, Jan 15, 2008 at 08:42:36PM -0800, Andrew Morton wrote:
> > > On Wed, 16 Jan 2008 12:25:53 +0800 Fengguang Wu <wfg@...l.ustc.edu.cn> wrote:
> > > 
> > > > list_heads are OK if we use them for one and only function.
> > > 
> > > Not really.  They're inappropriate when you wish to remember your
> > > position in the list while you dropped the lock (as we must do in
> > > writeback).
> > > 
> > > A data structure which permits us to interate across the search key rather
> > > than across the actual storage locations is more appropriate.
> > 
> > I totally agree with you. What I mean is to first do the split of
> > functions - into three: ordering, starvation prevention, and blockade
> > waiting.
> 
> Does "ordering" here refer to ordering bt time-of-first-dirty?

Ordering by dirtied_when or i_ino, either is OK.

> What is "blockade waiting"?

Some inodes/pages cannot be synced now for some reason and should be
retried after a while.

> > Then to do better ordering by adopting radix tree(or rbtree
> > if radix tree is not enough),
> 
> ordering of what?

Switch from time to location.

> > and lastly get rid of the list_heads to
> > avoid locking. Does it sound like a good path?
> 
> I'd have thaought that replacing list_heads with another data structure
> would be a simgle commit.

That would be easy. s_more_io and s_more_io_wait can all be converted
to radix trees.

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