Re: Linux responsiveness under heavy load

[Jamie Lokier <lk@tantalophile.demon.co.uk>]

Rik van Riel wrote:
> > A larger priority for page-in I/O due to interactive process too
> > might help too.  Some modification of Andrea's elevator.  But
> > that doesn't seem so easy.
> 
> Read requests are easily tied to a process, so this could
> be relatively easy. Doing it properly before 2.5 may be a
> little difficult though ...

A simple flag with each I/O request meaning "high priority due to
interactive process I/O".  Make the elevator select high priority
requests before low ones, with the same sequence number bound for
fairness as has recently been implemented.

Maybe even a small holdoff time when going from handling a high priority
to a low priority request, to give the interactive process a few
microseconds to stimulate another page in.  (Actually a small holdoff in
general between I/O "here" and I/O "far away" might improve overall seek
times, orthogonal to priority issues).

It does seem too simple to work, but has anyone tried it?

-- Jamie
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