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    SubjectRe: Clearing the I/O caches? (for benchmark tests)
    "Stephen C. Tweedie" <> writes:
    > Hi,
    Hey Stephen,

    > On 13 Jul 1999 16:10:38 -0700, (Tom M. Kroeger) said:
    > > My problem is that while I'm able to apparently clear the page
    > > directory and inode caches, I'm unable to completely clear the buffer
    > > cache. This is indicated by the fact that my benchmark sees a buffer
    > > cache hit ratio of 74% right after a reboot, but after the test has
    > > been run once I'm unable to get the buffer cache hit ratio below 78%.
    > > I understand that data that some data (e.g. open file meta data) can't
    > > be cleared, but once my benchmark test is finished, all of the data
    > > should be unlocked and freeable? correct?
    > Nearly. The ext2 filesystem keeps a cache of recently-accessed bitmap
    > buffers pinned in memory, and once that cache is primed you can't flush
    > it unless you unmount the filesystem. If you have any processes still
    > cd'ed to the active filesystem, then they will also be keeping directory
    > inodes pinned in the inode cache.

    ahhh.... ;-) thank you for the light!

    OK I can unmount /home, but is it reasonable to unmount /usr. I
    suspect a reboot might be the simplest thing.

    In any case the memory exhausting approach still cleared far more
    space than sys_sync & invalidate_buffers etc... (are these buffers
    taken from ext2 when memory becomes very low?) Any idea as to why?

    You said ext2 keeps "recently-accessed bitmap buffers pinned", can
    I just wait 30 second ( or however long) and then re-run the test?

    Again thanks for you time and help,



    Tom M. Kroeger Pray for wind
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