Messages in this thread |  | | | From | Benjamin Rutt <> | | Subject | Re: clearing filesystem cache for I/O benchmarks | | Date | Mon, 26 Jul 2004 09:02:45 -0400 |
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Andrew Morton <akpm@osdl.org> writes:
> Benjamin Rutt <rutt.4+news@osu.edu> wrote: >> >> How can I purge all of the kernel's filesystem caches, so I can trust >> that my I/O (read) requests I'm trying to benchmark bypass the kernel >> filesystem cache? > > Either delete the benchmark test files or
I'm not sure I follow. If I delete the benchmark files, I'll only need to create them again later in order to do a read test, and I'll have the same problem then, of how to eliminate the just-written-data from cache. Unless you're suggesting I write using some special mode that won't enter the written data into cache? (e.g. O_DIRECT?)
> , in 2.6, use fsync+posix_fadvise(POSIX_FADV_DONTNEED);
Thanks for the reference, I wasn't aware of that one. We are running some 2.4 kernels in our storage cluster unfortunately so that won't be usable for us everywhere. I take it POSIX_FADV_DONTNEED is ignored under 2.4.
A related question...if no posix_fadvise() advice has been given, does reading sequentially every byte of an 8GB file on a machine with <= 8GB of RAM guarantee that any page cache data that existed on the machine prior to the start of the 8GB read is now gone? -- Benjamin Rutt
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