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

From: Andrew Morton
Date: Fri Aug 18 2006 - 03:09:29 EST

On Fri, 18 Aug 2006 09:03:15 +0200
Jens Axboe <axboe@xxxxxxx> wrote:

> On Thu, Aug 17 2006, Andrew Morton wrote:
> > It seems that the many-writers-to-different-disks workloads don't happen
> > very often. We know this because
> >
> > a) The 2.4 performance is utterly awful, and I never saw anybody
> > complain and
> Talk to some of the people that used DVD-RAM devices (or other
> excruciatingly slow writers) on their system, and they would disagree
> violently :-)

umm, OK, I guess that has the same cause: buffer_heads from different
devices all on the same single queue. In this case the problem is that one
device is slow. In the same-speed-devices case the problem is that all
writeback threads get stuck on the same device, allowing others to go idle.

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