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

[Christoph Hellwig <hch@infradead.org>]

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.

> 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>