Messages in this thread | | | Date | Mon, 24 Jun 2002 14:34:31 -0700 | From | "Martin J. Bligh" <> | Subject | Re: [PATCH] (1/2) reverse mapping VM for 2.5.23 (rmap-13b) |
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>> I'll try a more varied set of tests tonight, with cpu usage tabulated. > > Please do a few non-swap tests too. > > Swapping is the thing that rmap is supposed to _help_, so improvements in > that area are good (and had better happen!), but if you're only looking at > the swap performance, you're ignoring the known problems with rmap, ie the > cases where non-rmap kernels do really well. > > Comparing one but not the other doesn't give a very balanced picture..
It would also be interesting to see memory consumption figures for a benchmark with many large processes. With this type of load, memory consumption through PTEs is already a problem - as far as I can see, rmap triples the memory requirement of PTEs through the PTE chain's doubly linked list (an additional 8 bytes per entry) ... perhaps my calculations are wrong? This is particular problem for databases that tend to have thousands of processes attatched to a large shared memory area.
A quick rough calculation indicates that the Oracle test I was helping out with was consuming almost 10Gb of PTEs without rmap - 30Gb for overhead doesn't sound like fun to me ;-(
M.
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