Re: [PATCH v1 4/8] iomap: add writepages support for IOMAP_IN_MEM iomaps

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Jun 09, 2025 at 08:49:25PM -0700, Christoph Hellwig wrote:
> On Mon, Jun 09, 2025 at 09:57:41AM -0700, Darrick J. Wong wrote:
> > > It might also be worth stating what you don't use.  One big thing
> > > that springs to mind is ioends.  Which are really useful if you
> > > need more than one request to handle a folio, something that is
> > > pretty common in network file systems.  I guess you don't need
> > > that for fuse?
> > 
> > My initial thought was "I wonder if Joanne would be better off with a
> > totally separate iomap_writepage_map_blocks implementation"
> 
> I think that's basically what the patches do, right?

Yes.

> > since I
> > *think* fuse just needs a callback from iomap to initiate FUSE_WRITE
> > calls on the dirty range(s) of a folio, and then fuse can call
> > mapping_set_error and iomap_finish_folio_write when those FUSE_WRITE
> > calls complete.  There are no bios, so I don't see much point in using
> > the ioend machinery.
> 
> Note that the mapping_set_error in iomap_writepage_map is only for
> synchronous errors for mapping setup anyway, all the actual I/O error
> are handled asynchronously anyway.  Similar, clearing the writeback
> bit only happens for synchronous erorr, or the rare case of (almost)
> synchronous I/O.

Heheh, my brain has gotten fuzzy on all that pagecache error handling
changes over the years.

--D