xfs: enable extent size hints for CoW when rtextsize > 1

CoW extent size hints are not allowed on filesystems that have large
realtime extents because we only want to perform the minimum required
amount of write-around (aka write amplification) for shared extents.

On filesystems where rtextsize > 1, allocations can only be done in
units of full rt extents, which means that we can only map an entire rt
extent's worth of blocks into the data fork.  Hole punch requests become
conversions to unwritten if the request isn't aligned properly.

Because a copy-write fundamentally requires remapping, this means that
we also can only do copy-writes of a full rt extent.  This is too
expensive for large hint sizes, since it's all or nothing.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>

0 files changed, 0 insertions, 0 deletions