hole punching performance

[Dave Chinner]

On Tue, Jan 15, 2013 at 06:33:54PM -0500, Bradley C. Kuszmaul wrote:
> So my understanding is that the first time I do a read() I'll have to read
> the extents.  My writes are on the order of a megabyte, a 250MB file will
> likely require an extra I/O to open.  That's fine.

write size != extent size.

Extents on XFS on a 4k block size filesystem can be up to 8GB in
size. It's entirely likely that your 250MB file is a single extent
an dhence has no extra overhead on read.  Use xfs_bmap to check.

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com