Re: [PATCHv8 4/5] iomap: Allocate iof in ->write_begin() early

[Christoph Hellwig <hch@infradead.org>]

On Tue, Jun 06, 2023 at 05:13:51PM +0530, Ritesh Harjani (IBM) wrote:
> We dont need to allocate an iof in ->write_begin() for writes where the
> position and length completely overlap with the given folio.
> Therefore, such cases are skipped.
> 
> Currently when the folio is uptodate, we only allocate iof at writeback
> time (in iomap_writepage_map()). This is ok until now, but when we are
> going to add support for per-block dirty state bitmap in iof, this
> could cause some performance degradation. The reason is that if we don't
> allocate iof during ->write_begin(), then we will never mark the
> necessary dirty bits in ->write_end() call. And we will have to mark all
> the bits as dirty at the writeback time, that could cause the same write
> amplification and performance problems as it is now.
> 
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

(and didn't I ack an earlier of this already?)