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    Subject[PATCH v2 13/27] mm: Add unlock_folio
    Date
    Convert unlock_page() to call unlock_folio().  By using a folio we avoid
    a call to compound_head(). This shortens the function from 39 bytes to
    25 and removes 4 instructions on x86-64. Those instructions are currently
    pushed into each caller, but subsequent patches will convert many of the
    callers to operate on folios.

    Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    ---
    include/linux/pagemap.h | 16 +++++++++++++++-
    mm/filemap.c | 27 ++++++++++-----------------
    2 files changed, 25 insertions(+), 18 deletions(-)

    diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
    index c27b74c63b5e..44675104008b 100644
    --- a/include/linux/pagemap.h
    +++ b/include/linux/pagemap.h
    @@ -623,7 +623,21 @@ extern int __lock_page_killable(struct page *page);
    extern int __lock_page_async(struct page *page, struct wait_page_queue *wait);
    extern int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
    unsigned int flags);
    -extern void unlock_page(struct page *page);
    +void unlock_folio(struct folio *folio);
    +
    +/**
    + * unlock_page - Unlock a locked page.
    + * @page: The page.
    + *
    + * Unlocks the page and wakes up any thread sleeping on the page lock.
    + *
    + * Context: May be called from interrupt or process context. May not be
    + * called from NMI context.
    + */
    +static inline void unlock_page(struct page *page)
    +{
    + return unlock_folio(page_folio(page));
    +}

    /*
    * Return true if the page was successfully locked
    diff --git a/mm/filemap.c b/mm/filemap.c
    index bb28dd6d9e22..31470b36ac89 100644
    --- a/mm/filemap.c
    +++ b/mm/filemap.c
    @@ -1438,29 +1438,22 @@ static inline bool clear_bit_unlock_is_negative_byte(long nr, volatile void *mem
    #endif

    /**
    - * unlock_page - unlock a locked page
    - * @page: the page
    + * unlock_folio - Unlock a locked folio.
    + * @folio: The folio.
    *
    - * Unlocks the page and wakes up sleepers in wait_on_page_locked().
    - * Also wakes sleepers in wait_on_page_writeback() because the wakeup
    - * mechanism between PageLocked pages and PageWriteback pages is shared.
    - * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
    + * Unlocks the folio and wakes up any thread sleeping on the page lock.
    *
    - * Note that this depends on PG_waiters being the sign bit in the byte
    - * that contains PG_locked - thus the BUILD_BUG_ON(). That allows us to
    - * clear the PG_locked bit and test PG_waiters at the same time fairly
    - * portably (architectures that do LL/SC can test any bit, while x86 can
    - * test the sign bit).
    + * Context: May be called from interrupt or process context. May not be
    + * called from NMI context.
    */
    -void unlock_page(struct page *page)
    +void unlock_folio(struct folio *folio)
    {
    BUILD_BUG_ON(PG_waiters != 7);
    - page = compound_head(page);
    - VM_BUG_ON_PAGE(!PageLocked(page), page);
    - if (clear_bit_unlock_is_negative_byte(PG_locked, &page->flags))
    - wake_up_page_bit(page, PG_locked);
    + VM_BUG_ON_FOLIO(!FolioLocked(folio), folio);
    + if (clear_bit_unlock_is_negative_byte(PG_locked, folio_flags(folio)))
    + wake_up_page_bit(&folio->page, PG_locked);
    }
    -EXPORT_SYMBOL(unlock_page);
    +EXPORT_SYMBOL(unlock_folio);

    /**
    * end_page_writeback - end writeback against a page
    --
    2.29.2
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