Date: Wed, 6 Dec 2000 11:05:33 -0800 (PST) From: Matt Dillon <dillon@earth.backplane.com> To: News History File User <newsuser@free-pr0n.netscum.dk> Cc: hackers@freebsd.org, usenet@tdk.net Subject: Re: vm_pageout_scan badness Message-ID: <200012061905.eB6J5XV96902@earth.backplane.com> References: <200012011918.eB1JIol53670@earth.backplane.com> <200012020525.eB25PPQ92768@newsmangler.inet.tele.dk> <200012021904.eB2J4An63970@earth.backplane.com> <200012030700.eB370XJ22476@newsmangler.inet.tele.dk> <200012040053.eB40rnm69425@earth.backplane.com> <200012050545.eB55jL453889@crotchety.newsbastards.org> <200012060519.eB65JS910042@crotchety.newsbastards.org> <200012060713.eB67D8I91529@earth.backplane.com> <200012061355.eB6DtGS34255@crotchety.newsbastards.org>
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Excellent.
What I believe is going on is that without the madvise()/mlock() the
general accesses to the 1 GB main history file are causing the pages to be
flushed from the .hash and .index files too quickly. The performance
problems in general appear to be due to the system trying to cache more
of the (essentially uncacheable) main history file at the expense of
not caching as much of the (emminently cacheable) .index and .hash files.
One possible fix would be to have the kernel track cache hits and misses
on a file and implement a heuristic from those statistics which is used
to reduce the 'initial page weighting' for pages read-in from the
'generally uncacheable file'. This would cause the kernel to reuse
those cache pages more quickly and prevent it from throwing away (reusing)
cache pages associated with more cacheable files like the .index and
.hash files. I don't have time to do this now, but it's definitely
something I am going to keep in mind for a later release.
-Matt
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