Re: [PATCH v2 2/5] xfs: flush eof folio before insert range size update

[Brian Foster <bfoster@redhat.com>]

On Tue, Feb 10, 2026 at 08:16:48AM -0800, Christoph Hellwig wrote:
> On Thu, Jan 29, 2026 at 10:50:25AM -0500, Brian Foster wrote:
> > The flush in xfs_buffered_write_iomap_begin() for zero range over a
> > data fork hole fronted by COW fork prealloc is primarily designed to
> > provide correct zeroing behavior in particular pagecache conditions.
> > As it turns out, this also partially masks some odd behavior in
> > insert range (via zero range via setattr).
> > 
> > Insert range bumps i_size the length of the new range, flushes,
> > unmaps pagecache and cancels COW prealloc, and then right shifts
> > extents from the end of the file back to the target offset of the
> > insert. Since the i_size update occurs before the pagecache flush,
> > this creates a transient situation where writeback around EOF can
> > behave differently.
> 
> Eww.
> 

Yes. I'd still like to have something better here. I just don't know
what that is. I'm hoping that more eyes on this little quirk will
eventually lead to some better ideas on the insert range side.

Thanks for the review.

Brian

> > To avoid this quirk, flush the EOF folio before the i_size update
> > during insert range. The entire range will be flushed, unmapped and
> > invalidated anyways, so this should be relatively unnoticeable.
> 
> Looks good:
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
>