Re: [PATCH v1 5/8] iomap: add iomap_writeback_dirty_folio()

[Christoph Hellwig <hch@infradead.org>]

On Mon, Jun 09, 2025 at 04:30:14PM -0700, Joanne Koong wrote:
> > When writing this code I was under the impression that
> > folio_end_writeback needs to be called after unlocking the page.
> >
> > If that is not actually the case we can just move the unlocking into the
> > caller and make things a lot cleaner than the conditional locking
> > argument.
> 
> I don't think we can move this into the caller of ->writeback_folio()
> / ->map_blocks(). iomap does some preliminary optimization checking
> (eg skipping writing back truncated ranges) in
> iomap_writepage_handle_eof() which will unlock the folio if succesful
> and is called separately from those callbacks. As well it's not clear
> for the caller to know when the folio can be unlocked (eg if the range
> being written back / mapped is the last range in that folio).

Note that with caller I meant the immediate caller of
iomap_writepage_map, i.e. iomap_writepages only for the existing code
that needs the unlock, and your new iomap_writeback_dirty_folio
that doesn't.