hole punching performance

[Bradley C. Kuszmaul]

But if I populate the file with a collection of near-1MB writes at random
offsets, I'm likely to end up with one extent per write.  Each non-hole
line in xfs_bmap is an extent, right?

-Bradley

On Tue, Jan 15, 2013 at 7:00 PM, Dave Chinner <david at fromorbit.com> wrote:

> 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
>
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