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SubjectRe: Clearing the I/O caches? (for benchmark tests)

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.


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