Messages in this thread | | | Date | Mon, 26 May 2008 15:33:18 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH -mm 00/16] VM pageout scalability improvements (V8) |
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On Mon, 26 May 2008 23:54:55 +0530 Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> Rik van Riel wrote: > > On large memory systems, the VM can spend way too much time scanning > > through pages that it cannot (or should not) evict from memory. Not > > only does it use up CPU time, but it also provokes lock contention > > and can leave large systems under memory presure in a catatonic state. > > Hi, Rik, > > This patchset looks good (I did a brief scan). I'll go ahead and play with it? > What is a good memory size to test the patches on (to see improvements).
The larger, the better. One known problem with the current upstream VM is large numbers of anonymous pages, or a mix of mlocked and anon pages.
Once the system needs to swap something out, every single anon page will have the referenced bit set and the system needs to do lots of scanning before it can evict the first page. This scanning causes multiple CPUs to pile up and things slow down exponentially and/or catastrophically :)
Unfortunately the largest system I have access to on a regular basis has "only" 16GB of RAM :(
I am also making 2.6.25 based kernel RPMs available with the split LRU patch set, at http://people.redhat.com/riel/splitvm/
The most recently posted patches are newer, though...
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