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    Subject[PATCH v4 12/25] mm/filemap: 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. Because we still
    have unlock_page(), it's a net increase of 24 bytes of text.

    Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    ---
    include/linux/pagemap.h | 3 ++-
    mm/filemap.c | 27 ++++++++++-----------------
    mm/folio-compat.c | 6 ++++++
    3 files changed, 18 insertions(+), 18 deletions(-)

    diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
    index 5a2c0764d7c0..a34cf531c100 100644
    --- a/include/linux/pagemap.h
    +++ b/include/linux/pagemap.h
    @@ -640,7 +640,8 @@ 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_page(struct page *page);
    +void unlock_folio(struct folio *folio);

    /*
    * Return true if the page was successfully locked
    diff --git a/mm/filemap.c b/mm/filemap.c
    index 3d1635d3be3e..9960ef1b2758 100644
    --- a/mm/filemap.c
    +++ b/mm/filemap.c
    @@ -1408,29 +1408,22 @@ 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
    diff --git a/mm/folio-compat.c b/mm/folio-compat.c
    index 5e107aa30a62..02798abf19a1 100644
    --- a/mm/folio-compat.c
    +++ b/mm/folio-compat.c
    @@ -11,3 +11,9 @@ struct address_space *page_mapping(struct page *page)
    return folio_mapping(page_folio(page));
    }
    EXPORT_SYMBOL(page_mapping);
    +
    +void unlock_page(struct page *page)
    +{
    + return unlock_folio(page_folio(page));
    +}
    +EXPORT_SYMBOL(unlock_page);
    --
    2.30.0
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