Re: [PATCH] mm: Implement swap prefetching tweaks

[Mike Galbraith <efault@gmx.de>]

On Sat, 2006-03-11 at 23:54 -0500, Lee Revell wrote:
> On Sat, 2006-03-11 at 08:51 +0100, Mike Galbraith wrote:
> > There used to be a pages in flight 'restrictor plate' in there that
> > would have probably helped this situation at least a little.  But in
> > any case, it sounds like you'll have to find a way to submit the IO in
> > itty bitty synchronous pieces. 
> 
> echo 64 > /sys/block/hd*/queue/max_sectors_kb
> 
> There is basically a straight linear relation between whatever you set
> this to and the maximum scheduling latency you see.  It was developed to
> solve the exact problem you are describing.

Ah, a very useful bit of information, thanks.

It won't help Con though, because he'll be dealing with every possible
configuration.  I think he's going to have to either submit, wait,
bandwidth limiting sleep, repeat or something clever that does that.
Even with bandwidth restriction though, seek still bites mightily, so I
suspect he's stuck with little trickles of IO started when we'd
otherwise be idle.  We'll see I suppose.

	-Mike