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

[Jan Kara]

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
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...

								Honza

> 
> ---
> Tal Zussman (11):
>       mm: add folio_wake_writeback() helper
>       folio_wait: move folio bit-lock and wait implementation to mm/folio_wait.c
>       folio_wait: move folio bit-lock and wait declarations to include/linux/folio_wait.h
>       folio_wait: move folio_wait_writeback() family to mm/folio_wait.c
>       folio_wait: reformat comments and fix alignment
>       folio_wait: rename wait_page_* infrastructure to wait_folio_*
>       folio_wait: convert VM_BUG_ON_FOLIO() to VM_WARN_ON_ONCE_FOLIO()
>       MAINTAINERS: add folio_wait files to MEMORY MANAGEMENT - CORE
>       fs: move dir_pages() from <linux/pagemap.h> to <linux/fs.h>
>       fs: move generic_file_read_iter() to fs/read_write.c
>       fs: move generic_file_write_iter() family to fs/read_write.c
> 
>  MAINTAINERS                |   2 +
>  fs/read_write.c            | 358 ++++++++++++++++
>  include/linux/folio_wait.h | 183 +++++++++
>  include/linux/fs.h         |  19 +-
>  include/linux/pagemap.h    | 184 +--------
>  io_uring/rw.c              |  14 +-
>  io_uring/rw.h              |   6 +-
>  mm/Makefile                |   2 +-
>  mm/filemap.c               | 993 +--------------------------------------------
>  mm/folio_wait.c            | 710 ++++++++++++++++++++++++++++++++
>  mm/internal.h              |   4 +
>  mm/page-writeback.c        |  66 ---
>  12 files changed, 1285 insertions(+), 1256 deletions(-)
> ---
> base-commit: e9add7501ad3297dad9b90ce201266830a68ab47
> change-id: 20260511-filemap-split-871b5c18e98c
> 
> Best regards,
> -- 
> Tal Zussman <tz2294@xxxxxxxxxxxx>
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR