Re: [PATCH] mm: Implement swap prefetching tweaks

[Con Kolivas <kernel@kolivas.org>]

On Saturday 11 March 2006 15:28, Peter Williams wrote:
> Con Kolivas wrote:
> > Because despite what anyone seems to want to believe, reading from disk
> > hurts. Why it hurts so much I'm not really sure, but it's not a SCSI vs
> > IDE with or without DMA issue. It's not about tweaking parameters. It
> > doesn't seem to be only about cpu cycles. This is not a mistuned system
> > that it happens on. It just plain hurts if we do lots of disk i/o,
> > perhaps it's saturating the bus or something. Whatever it is, as much as
> > I'd _like_ swap prefetch to just keep working quietly at ultra ultra low
> > priority, the disk reads that swap prefetch does are not innocuous so I
> > really do want them to only be done when nothing else wants cpu.

I didn't make it clear here the things affected are not even doing any I/O of 
their own. It's not about I/O resource allocation. However they are using 
100% cpu and probably doing a lot of gpu bus traffic.

> Would you like to try a prototype version of the soft caps patch I'm
> working on to see if it will help?

What happens if it's using .01% cpu and spends most of its time in 
uninterruptible sleep?

Cheers,
Con