Messages in this thread | | | Date | Tue, 9 Dec 2003 17:31:49 +0100 | From | Roger Luethi <> | Subject | Re: 2.6.0-test9 - poor swap performance on low end machines |
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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.
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