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    Subject[PATCH v3 00/25] Page folios
    Date
    Some functions which take a struct page as an argument operate on
    PAGE_SIZE bytes. Others operate on the entire compound page if
    passed either a head or tail page. Others operate on the compound
    page if passed a head page, but PAGE_SIZE bytes if passed a tail page.
    Yet others either BUG or do the wrong thing if passed a tail page.

    This patch series starts to resolve this ambiguity by introducing a new
    type, the struct folio. A function which takes a struct folio argument
    declares that it will operate on the entire page. In return, the caller
    guarantees that the pointer it is passing does not point to a tail page.

    This allows us to do less work. Now we have a type that is guaranteed
    not to be a tail page, we can avoid calling compound_head(). That saves
    us hundreds of bytes of text and even manages to reduce the amount of
    data in the kernel image somehow.

    The focus for this patch series is on introducing infrastructure.
    The big correctness proof that exists in this patch series is to make
    it clear that one cannot wait (for the page lock or writeback) on a
    tail page. I don't believe there were any places which could miss a
    wakeup due to this, but it's hard to prove that without struct folio.
    Now the compiler proves it for us.

    v3:
    - Rebase on next-20210127. Two major sources of conflict, the
    generic_file_buffered_read refactoring (in akpm tree) and the
    fscache work (in dhowells tree). Not sure how this patch series
    can get merged with these two sources of conflict?
    v2:
    - Pare patch series back to just infrastructure and the page waiting
    parts.

    Matthew Wilcox (Oracle) (25):
    mm: Introduce struct folio
    mm: Add folio_pgdat
    mm/vmstat: Add folio stat wrappers
    mm/debug: Add VM_BUG_ON_FOLIO and VM_WARN_ON_ONCE_FOLIO
    mm: Add put_folio
    mm: Add get_folio
    mm: Create FolioFlags
    mm: Handle per-folio private data
    mm: Add folio_index, folio_page and folio_contains
    mm/util: Add folio_mapping and folio_file_mapping
    mm/memcg: Add folio_memcg, lock_folio_memcg and unlock_folio_memcg
    mm/memcg: Add mem_cgroup_folio_lruvec
    mm: Add unlock_folio
    mm: Add lock_folio
    mm: Add lock_folio_killable
    mm: Convert lock_page_async to lock_folio_async
    mm/filemap: Convert end_page_writeback to end_folio_writeback
    mm: Convert wait_on_page_bit to wait_on_folio_bit
    mm: Add wait_for_stable_folio and wait_on_folio_writeback
    mm: Add wait_on_folio_locked & wait_on_folio_locked_killable
    mm: Convert lock_page_or_retry to lock_folio_or_retry
    mm/filemap: Convert wake_up_page_bit to wake_up_folio_bit
    mm: Convert test_clear_page_writeback to test_clear_folio_writeback
    mm/filemap: Convert page wait queues to be folios
    cachefiles: Switch to wait_page_key

    fs/afs/write.c | 31 +++---
    fs/cachefiles/rdwr.c | 13 ++-
    fs/io_uring.c | 2 +-
    include/linux/memcontrol.h | 22 ++++
    include/linux/mm.h | 88 ++++++++++++----
    include/linux/mm_types.h | 33 ++++++
    include/linux/mmdebug.h | 20 ++++
    include/linux/netfs.h | 5 +
    include/linux/page-flags.h | 106 +++++++++++++++----
    include/linux/pagemap.h | 201 ++++++++++++++++++++++++-----------
    include/linux/vmstat.h | 60 +++++++++++
    mm/filemap.c | 207 ++++++++++++++++++-------------------
    mm/memcontrol.c | 36 ++++---
    mm/memory.c | 10 +-
    mm/page-writeback.c | 48 ++++-----
    mm/swapfile.c | 6 +-
    mm/util.c | 20 ++--
    17 files changed, 621 insertions(+), 287 deletions(-)

    --
    2.29.2

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