Messages in this thread | | | From | Heinz Mauelshagen <> | Subject | Re: [patch] dynamic buffer cache hash table size | Date | Fri, 22 Jan 1999 15:18:05 MET |
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> > On Thu, 21 Jan 1999, Andrea Arcangeli wrote: > > > On Thu, 21 Jan 1999, Heinz Mauelshagen wrote: > > > > > - buffermem is 200M of my 256M system afterwards > > > - minimum swap. > > > - lots of system time searching the buffer cache with > > > commands afterwards. > > > > so the problem is just only the ~O(n) search in the buffer cache right? > > > > > - commands running 50 to 100!!! times slower than before filling buffercache > > > > No this is a workaround of the problem I think that right now I should > > enlarge the buffer hash table of the buffer headers for high memory > > machines. > > I've done that now. Worked fine here so far. I am allocating now 65 pages > for my 128Mbyte RAM machine. In 64Mbyte the pages allocated for the buffer > hash table will be 33 (continue linear...). Maybe it's too much? > > Could you try out if this patch against pre-8.gz (in testing) fix the `too > much allocated buffers' problem without having to set max limit on the > buffer cache? > > BTW, since I was there I also enlarged the page cache hash table from > 8kbyte (2k entry) to 32kbyte (8k entries) since with 128Mbyte I don't care > to lose 1 page and half to go 4 time faster (if I guess the math right) > while browsing the cache.
Added the patch.
The bad performance nearly stays the same, when the buffermem is large 8*( Only adding my artificial limitation for the buffermem to limit it to for eg. 20M is almost fine.
The mke2fs of the 12G devices nearly works twice as fast (2:35 minutes vs 4:50 minutes) and the command performance only drops from 0.4s real to 2.3 real and not to more than 30s real.
I think that CPU cache trashing with a buffer amount of 200M might be the big issue for my performance loss?!
Regards, Heinz
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Systemmanagement Entwicklungsbereich 2 Deutsche Telekom AG Entwicklungszentrum Darmstadt Heinz Mauelshagen Otto-Roehm-Strasse 71c Postfach 10 05 41 mge@ez-darmstadt.telekom.de 64205 Darmstadt Germany +49 6151 886-425 FAX-386 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
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Systemmanagement Entwicklungsbereich 2 Deutsche Telekom AG Entwicklungszentrum Darmstadt Heinz Mauelshagen Otto-Roehm-Strasse 71c Postfach 10 05 41 mge@ez-darmstadt.telekom.de 64205 Darmstadt Germany +49 6151 886-425 FAX-386 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
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