[lkml]   [2004]   [Jul]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: clearing filesystem cache for I/O benchmarks
Andrew Morton <> writes:

> Benjamin Rutt <> 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

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2005-03-22 14:04    [from the cache]
©2003-2014 Jasper Spaans. hosted at Digital Ocean