does fuse need ->launder_folios, was: Re: [PATCH v1 5/8] iomap: add iomap_writeback_dirty_folio()

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jun 11, 2025 at 05:34:50AM +0100, Matthew Wilcox wrote:
> > My memory might be betraying me, but I think willy once launched an
> > attempt to see if we can kill launder_folio.  Adding him, and the
> > mm and nfs lists to check if I have a point :)
> 
> I ... got distracted with everything else.
> 
> Looking at the original addition of ->launder_page (e3db7691e9f3), I
> don't understand why we need it.  invalidate_inode_pages2() isn't
> supposed to invalidate dirty pages, so I don't understand why nfs
> found it necessary to do writeback from ->releasepage() instead
> of just returning false like iomap does.

Yeah.  Miklos (and other fuse folks), can you help figuring out
if fuse really wants ->launder_folio?  Because it would be really good
to settle this question before we have to add iomap infrastruture for
it.