Re: 2.6.0-test9 - poor swap performance on low end machines

Roger Luethi
2003-12-09T16:32:55Z

On Tue, 09 Dec 2003 11:04:49 -0500, Rik van Riel wrote:
> > The classic strategies based on these criteria work for transaction and
> > batch systems. They are all but useless, though, for a workstation and
> > even most modern servers, due to assumptions that are incorrect today
> > (remember all the degrees of freedom a scheduler had 30 years ago)
> > and additional factors that only became crucial in the past few decades
> > (latency again).
>
> Don't forget that computers have gotten a lot slower
> over the years ;)
>
> Swapping out a 64kB process to a disk that does 180kB/s
> is a lot faster than swapping out a 100MB process to a
> disk that does 50MB/s ...
>
> Once you figure in seek times, the picture looks even
> worse.

Exactly -- I did mention the growing access time gap between RAM and
disks in an earlier message. Yes, there are quite a few developments in
hardware and in the way we use computers (interactive, Client/Server,
dedicated machines, etc.) that made thrashing pretty much unsolvable
at an OS level. Fortunately, fixing it in hardware by adding RAM works
for most.

What we _can_ do in software, though, is prevent thrashing as long as
possible. Comparing 2.4 and 2.6 shows that a kernel can still make a
significant difference with smart pageout algorithms, I/O scheduling etc.
But you won't get much help with that from ancient papers.

Roger