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

[David Chinner <dgc@sgi.com>]

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@mail.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@chello.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