strict allocate

[Jeremy Allison]

On Tue, Dec 01, 2009 at 05:56:59PM +0100, Björn JACKE wrote:
> Hi,
> 
> bug 6942 beamed by attention to this article:
> 
> http://software.intel.com/en-us/articles/windows-client-cifs-behavior-can-slow-linux-nas-performance/
> 
> It might be a good idea to change the default of strict allocate to "yes". This
> makes out-of-quota situation less error prone and scenarios like in that article
> will improve, too.
> 
> Has anyone strong feelings against that change of defaults?

Yes, don't do this. It's improves performance for some
cases, but kills performance for others. It's an ext3-only
fix as well, which doesn't work for ext4. Admittedly ext3
is our most common filesystem for now, but that won't always
be the case.

> In addition to that: When available, we could do allocation with
> posix_fallocate(), which has the additional benefit that with recent
> Linux
> kernels and advanced filesystems, allocation is being done at
> kernel/filesystem
> layer via fallocate with quasi zero overhead.

Look at https://bugzilla.samba.org/show_bug.cgi?id=6942
where there is a patch I did a while ago (modified since
then I think) that changes strict allocate to a tri-state
where the setting "partial" does most of what you want.

Jeremy.