Re: Bug#605009: serious performance regression with ext4
On Tue, Nov 30, 2010 at 10:35:11AM +0100, Samuel Thibault wrote:
> Mike Hommey, le Tue 30 Nov 2010 10:07:55 +0100, a écrit :
> > On Mon, Nov 29, 2010 at 07:18:17AM +0100, Guillem Jover wrote:
> > > Hmm, ok so what about posix_fadvise(fd, 0, 0, POSIX_FADV_DONTNEED)
> > > instead, skimming over the kernel source seems to indicate it might
> > > end up doing more or less the same thing but in a portable way?
> > On the other hand, there is no guarantee that other kernels do the same,
> Err, that's posix.
What is POSIX? What exactly is written in the standard? Please quote.
Okay, here is the quote[1]:
| POSIX_FADV_DONTNEED
| Specifies that the application expects that it will not access the
| specified data in the near future.
sync_file_range is Linux-specific and documented to do exactly what we
want[2]. posix_fadvise with POSIX_FADV_DONTNEED is not documented to do
what we want but only does it as a side-effect (and may hurt others
because it evicts anything of the cache).
Bastian
[1]: http://www.opengroup.org/onlinepubs/9699919799/functions/posix_fadvise.html
[2]: fs/sync.c
--
"That unit is a woman."
"A mass of conflicting impulses."
-- Spock and Nomad, "The Changeling", stardate 3541.9
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