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    SubjectRe: PERF: performance tests with the split LRU VM in -mm
    Date
    Hi,

    Rik van Riel <riel@redhat.com> writes:

    > In order to get the performance of the split LRU VM (in -mm) better,
    > I have performed several performance tests with the following kernels:
    > - 2.6.26 "2.6.26"
    > - 2.6.26-rc8-mm1 "-mm"
    > - 2.6.26-rc8-mm1 w/ "evict streaming IO cache first" patch "stream"
    > Patch at: http://lkml.org/lkml/2008/7/15/465
    > - 2.6.26-rc8-mm1 w/ "fix swapout on sequential IO" patch "noforce"
    > Patch at: http://marc.info/?l=linux-mm&m=121683855132630&w=2
    >
    > I have run the performance tests on a Dell pe1950 system
    > with 2 quad-core CPUs, 16GB of RAM and a hardware RAID 1
    > array of 146GB disks.
    >
    > The tests are fairly simple, but took a fair amount of time to
    > run due to the size of the data set involved (full disk for dd,
    > 55GB innodb file for the database tests).
    >
    >
    > TEST 1: dd if=/dev/sda of=/dev/null bs=1M
    >
    > kernel speed swap used
    >
    > 2.6.26 111MB/s 500kB
    > -mm 110MB/s 59MB (ouch, system noticably slower)
    > noforce 111MB/s 128kB
    > stream 108MB/s 0 (slight regression, not sure why yet)
    >
    > This patch shows that the split LRU VM in -mm has a problem
    > with large streaming IOs: the working set gets pushed out of
    > memory, which makes doing anything else during the big streaming
    > IO kind of painful.
    >
    > However, either of the two patches posted fixes that problem,
    > though at a slight performance penalty for the "stream" patch.

    Btw, my desktop machine runs -mm (+ the patch I have posted later in
    this thread) for over a week now and I have not yet encountered any
    notable regressions in normal usage patterns.

    I have not collected hard numbers but just tried to work normally with
    it.

    I also employed a massive memory eater (besides emacs and firefox) that
    spawns children that eat, serialized, ~120% of RAM each.

    Continuing normal work on both kernels was a bit harder, sure, but not
    impossible.

    The box never died on me nor did it thrash perceivably harder/longer
    near oom than .26. The oom killer was never invoked.

    Hannes


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