Re: RFC - how to balance Dirty+Writeback in the face of slow writeback.

David Chinner
2006-08-28T01:28:56Z

On Fri, Aug 25, 2006 at 08:37:24AM +0200, Jens Axboe wrote:
> On Fri, Aug 25 2006, Neil Brown wrote:
>
> > I'm beginning to think that the current scheme really works very well
> > - except for a few 'bugs'(*).
>
> It works ok, but it makes it hard to experiment with larger queue depths
> when the vm falls apart :-). It's not a big deal, though, even if the
> design isn't very nice - nr_requests is not a well defined entity. It
> can be anywhere from 512b to megabyte(s) in size. So throttling on X
> number of requests tends to be pretty vague and depends hugely on the
> workload (random vs sequential IO).

So maybe we need a different control parameter - the amount of memory we
allow to be backed up in a queue rather than the number of requests the
queue can take...

Cheers,

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