Re: [RFC PATCH v4 8/8] xfs: improve truncate on a realtime inode with huge extsize

[Christoph Hellwig]

On Fri, May 31, 2024 at 07:12:10AM -0700, Darrick J. Wong wrote:
> There are <cough> some users that want 1G extents.
> 
> For the rest of us who don't live in the stratosphere, it's convenient
> for fsdax to have rt extents that match the PMD size, which could be
> large on arm64 (e.g. 512M, or two smr sectors).

That's fine.  Maybe to rephrase my question.  With this series we
have 3 different truncate path:

 1) unmap all blocks (!rt || rtextsizse == 1)
 2) zero leftover blocks in an rtextent (small rtextsize, but > 1)
 3) converted leftover block in an rtextent to unwritten (large
   rtextsize)

What is the right threshold to switch between 2 and 3?  And do we
really need 2) at all?