Re: [patch 3/8] per backing_dev dirty and writeback page accounting

[David Chinner]

On Tue, Mar 06, 2007 at 07:04:46PM +0100, Miklos Szeredi wrote:
> From: Andrew Morton <akpm@xxxxxxxx>
> 
> [tomoki.sekiyama.qu@xxxxxxxxxxx: bugfix]
> 
> Miklos Szeredi <mszeredi@xxxxxxx>:
> 
> Changes:
>  - updated to apply after clear_page_dirty_for_io() race fix
> 
> This is needed for
> 
>  - balance_dirty_pages() deadlock fix
>  - fuse dirty page accounting
> 
> I have no idea how serious the scalability problems with this are.  If
> they are serious, different solutions can probably be found for the
> above, but this is certainly the simplest.

Atomic operations to a single per-backing device from all CPUs at once?
That's a pretty serious scalability issue and it will cause a major
performance regression for XFS.

I'd call this a showstopper right now - maybe you need to look at
something like the ZVC code that Christoph Lameter wrote, perhaps?

Cheers,

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