Re: Introduce SEEK_DATA/SEEK_HOLE to XFS V5

[Ben Myers <bpm@xxxxxxx>]

On Thu, Jan 12, 2012 at 11:41:48AM -0500, Christoph Hellwig wrote:
> On Thu, Jan 12, 2012 at 09:01:48AM -0600, Mark Tinguely wrote:
> > >Sorry, am was well understood your opinions in this point for now.
> > >IMHO, we can only find and return the data buffer offset at a dirty or
> > >unwritten page once the first page was probed.
> > >
> > 
> > From my tests, xfs_bmapi_read() can only find holes if they cross or
> > start on a 64KB boundary. It would be nice if unwritten extents were
> > at least that good at finding holes.
> 
> Are you testing on ia64 with 64k blocks? :)  xfs_bmapi_read will
> find holes down to block granularity, that's how it's implemented.
> However recent XFS does fairly aggressive preallocation, so you probably
                                                ^^^^
                                               
it is speculative delay in this case, I think.

-Ben

> won't find small holes unless you explicitly punch them out using
> XFS_IOC_UNRESVSP or fallocate with the hole punch flag.