Re: [PATCH RFC 00/11] mm/filemap: split out folio wait and VFS code

[Christian Brauner]

On Thu, May 28, 2026 at 11:22:37AM +0200, Jan Kara wrote:
> On Wed 20-05-26 16:48:51, Tal Zussman wrote:
> > mm/filemap.c has accumulated additional infrastructure over the years
> > that is not directly related to the page cache. It is currently nearly
> > 5000 lines long. This series splits out the folio bit-lock and wait
> > queue code into separate files, and moves the VFS-level
> > generic_file_{read,write}_iter() family of files to fs/read_write.c, in
> > order to provide better separation of concerns. This also slims down
> > mm/filemap.c by ~1000 lines.
> > 
> > The folio wait infrastructure is centralized in mm/folio_wait.c and
> > include/linux/folio_wait.h, with functions moved from mm/filemap.c,
> > mm/page-writeback.c, and include/linux/pagemap.h. Afterwards, the code
> > is cleaned up a little, with functions and data types renamed to refer
> > to folios rather than pages.
> > 
> > generic_file_{read,write}_iter() implement the VFS-level read/write path
> > for filesystems, including support for direct I/O. These functions and
> > their helpers are moved to fs/read_write.c, along with other VFS-level
> > read/write functions. dir_pages() is also moved to include/linux/fs.h.
> > i_blocks_per_folio() is not moved from include/linux/pagemap.h, as it
> > requires folio_size(), which is not currently available in
> > include/linux/fs.h.
> > 
> > No functional change is intended.
> > 
> > Note: I have additional cleanups to mm/filemap.c ready to go, foremost
> > among them centralizing on the filemap_*() naming convention and making
> > the exposed page cache API clearer and more consistent, but I've split
> > these patches off from that in order to avoid sending these logically
> > separate patches to ~60 maintainers.
> 
> Overall this makes sense to me. In particular I agree it makes sense to
> move the file read/write helpers into fs. Regarding the page waiting bits

Seconded.

> it makes some sense to me as well although there it's more of "I don't
> really care" opinion so let's see what Matthew and others think...

Agreed.