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

Fengguang Wu
2007-08-24T13:55:25Z

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