Messages in this thread | | | Subject | Re: Clearing the I/O caches? (for benchmark tests) | From | (Tom M. Kroeger) | Date | 14 Jul 1999 16:42:47 -0700 |
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"Stephen C. Tweedie" <sct@redhat.com> writes: > Hi, Hey Stephen,
> On 13 Jul 1999 16:10:38 -0700, tmk@cse.ucsc.edu (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,
--
tmk
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