Re: [PATCHSET v6.0 5/5] xfs: reflink with large realtime extents

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Dec 13, 2024 at 12:30:56AM -0800, Christoph Hellwig wrote:
> On Thu, Dec 12, 2024 at 04:57:58PM -0800, Darrick J. Wong wrote:
> > Hi all,
> > 
> > Now that we've landed support for reflink on the realtime device for
> > cases where the rt extent size is the same as the fs block size, enhance
> > the reflink code further to support cases where the rt extent size is a
> > power-of-two multiple of the fs block size.  This enables us to do data
> > block sharing (for example) for much larger allocation units by dirtying
> > pagecache around shared extents and expanding writeback to write back
> > shared extents fully.
> 
> FYI, I'd really like to avoid us pushing the large allocation sizes
> further than we have to.  Or in other words, unless we have a really
> important use case for this I'd prefer not to merge this code.

It's basically there in case (a) someone really wants cow amplification
on the realtime device or (b) something to base forcealign cow off of.
AFAICT it works, but seems a bit gross.

--D