Re: [PATCH v10 00/33] Memory folios

[William Kucharski]

I have a nit on part 01/33, but will respond directly there.

For the series:

Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>

> On May 11, 2021, at 3:47 PM, Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> wrote:
> 
> Managing memory in 4KiB pages is a serious overhead.  Many benchmarks
> benefit from a larger "page size".  As an example, an earlier iteration
> of this idea which used compound pages (and wasn't particularly tuned)
> got a 7% performance boost when compiling the kernel.
> 
> Using compound pages or THPs exposes a weakness of our type system.
> Functions are often unprepared for compound pages to be passed to them,
> and may only act on PAGE_SIZE chunks.  Even functions which are aware of
> compound pages may expect a head page, and do the wrong thing if passed
> a tail page.
> 
> We also waste a lot of instructions ensuring that we're not looking at
> a tail page.  Almost every call to PageFoo() contains one or more hidden
> calls to compound_head().  This also happens for get_page(), put_page()
> and many more functions.  There does not appear to be a way to tell gcc
> that it can cache the result of compound_head(), nor is there a way to
> tell it that compound_head() is idempotent.
> 
> This patch series uses a new type, the struct folio, to manage memory.
> It provides some basic infrastructure that's worthwhile in its own right,
> shrinking the kernel by about 5kB of text.
> 
> Since v9:
> - Rebase onto mmotm 2021-05-10-21-46
> - Add folio_memcg() definition for !MEMCG (intel lkp)
> - Change folio->private from an unsigned long to a void *
> - Use folio_page() to implement folio_file_page()
> - Add folio_try_get() and folio_try_get_rcu()
> - Trim back down to just the first few patches, which are better-reviewed.
> v9: https://lore.kernel.org/linux-mm/20210505150628.111735-1-willy@xxxxxxxxxxxxx/
> v8: https://lore.kernel.org/linux-mm/20210430180740.2707166-1-willy@xxxxxxxxxxxxx/
> 
> Matthew Wilcox (Oracle) (33):
>  mm: Introduce struct folio
>  mm: Add folio_pgdat and folio_zone
>  mm/vmstat: Add functions to account folio statistics
>  mm/debug: Add VM_BUG_ON_FOLIO and VM_WARN_ON_ONCE_FOLIO
>  mm: Add folio reference count functions
>  mm: Add folio_put
>  mm: Add folio_get
>  mm: Add folio_try_get_rcu
>  mm: Add folio flag manipulation functions
>  mm: Add folio_young and folio_idle
>  mm: Handle per-folio private data
>  mm/filemap: Add folio_index, folio_file_page and folio_contains
>  mm/filemap: Add folio_next_index
>  mm/filemap: Add folio_offset and folio_file_offset
>  mm/util: Add folio_mapping and folio_file_mapping
>  mm: Add folio_mapcount
>  mm/memcg: Add folio wrappers for various functions
>  mm/filemap: Add folio_unlock
>  mm/filemap: Add folio_lock
>  mm/filemap: Add folio_lock_killable
>  mm/filemap: Add __folio_lock_async
>  mm/filemap: Add __folio_lock_or_retry
>  mm/filemap: Add folio_wait_locked
>  mm/swap: Add folio_rotate_reclaimable
>  mm/filemap: Add folio_end_writeback
>  mm/writeback: Add folio_wait_writeback
>  mm/writeback: Add folio_wait_stable
>  mm/filemap: Add folio_wait_bit
>  mm/filemap: Add folio_wake_bit
>  mm/filemap: Convert page wait queues to be folios
>  mm/filemap: Add folio private_2 functions
>  fs/netfs: Add folio fscache functions
>  mm: Add folio_mapped
> 
> Documentation/core-api/mm-api.rst           |   4 +
> Documentation/filesystems/netfs_library.rst |   2 +
> fs/afs/write.c                              |   9 +-
> fs/cachefiles/rdwr.c                        |  16 +-
> fs/io_uring.c                               |   2 +-
> include/linux/memcontrol.h                  |  63 ++++
> include/linux/mm.h                          | 174 ++++++++--
> include/linux/mm_types.h                    |  71 ++++
> include/linux/mmdebug.h                     |  20 ++
> include/linux/netfs.h                       |  77 +++--
> include/linux/page-flags.h                  | 230 ++++++++++---
> include/linux/page_idle.h                   |  99 +++---
> include/linux/page_ref.h                    | 158 ++++++++-
> include/linux/pagemap.h                     | 358 ++++++++++++--------
> include/linux/swap.h                        |   7 +-
> include/linux/vmstat.h                      | 107 ++++++
> mm/Makefile                                 |   2 +-
> mm/filemap.c                                | 315 ++++++++---------
> mm/folio-compat.c                           |  43 +++
> mm/internal.h                               |   1 +
> mm/memory.c                                 |   8 +-
> mm/page-writeback.c                         |  72 ++--
> mm/page_io.c                                |   4 +-
> mm/swap.c                                   |  18 +-
> mm/swapfile.c                               |   8 +-
> mm/util.c                                   |  59 ++--
> 26 files changed, 1374 insertions(+), 553 deletions(-)
> create mode 100644 mm/folio-compat.c
> 
> -- 
> 2.30.2
> 
>