Re: [PATCH 04/23] page-writeback: Convert write_cache_pages() to use filemap_get_folios_tag()

[Matthew Wilcox]

On Fri, Nov 04, 2022 at 11:32:35AM +1100, Dave Chinner wrote:
> At minimum, it needs to be documented, though I'd much prefer that
> we explicitly duplicate write_cache_pages() as write_cache_folios()
> with a callback that takes a folio and change the code to be fully
> multi-page folio safe. Then filesystems that support folios (and
> large folios) natively can be passed folios without going through
> this crappy "folio->page, page->folio" dance because the writepage
> APIs are unaware of multi-page folio constructs.

There are a lot of places which go through the folio->page->folio
dance, and this one wasn't even close to the top of my list.  That
said, it has a fairly small number of callers -- ext4, fuse, iomap,
mpage, nfs, orangefs.  So Vishal, this seems like a good project for you
to take on next -- convert write_cache_pages() to write_cache_folios()
and writepage_t to write_folio_t.