Messages in this thread | | | Date | Thu, 28 Jun 2001 13:27:39 +0200 | From | Helge Hafting <> | Subject | Re: VM Requirement Document - v0.0 |
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Martin Knoblauch wrote:
> > maybe more specific: If the hit-rate is low and the cache is already > 70+% of the systems memory, the chances maybe slim that more cache is > going to improve the hit-rate. > Oh, but this is posible. You can get into situations where the (file cache) working set needs 80% or so of memory to get a near-perfect hitrate, and where using 70% of memory will trash madly due to the file access pattern. And this won't be a problem either, if the working set of "other" (non-file) stuff is below 20% of memory. The total size of non-file stuff may be above 20% though, so something goes into swap.
I definitely want the machine to work under such circumstances, so an arbitrary limit of 70% won't work.
Preventing swap-trashing at all cost doesn't help if the machine loose to io-trashing instead. Performance will be just as much down, although perhaps more satisfying because people aren't that surprised if explicit file operations take a long time. They hate it when moving the mouse or something cause a disk access even if their apps runs faster. :-(
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