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    Subject[PATCH v6 23/27] mm/writeback: Add wait_on_folio_writeback
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    wait_on_page_writeback_killable() only has one caller, so convert it to
    call wait_on_folio_writeback_killable(). For the wait_on_page_writeback()
    callers, add a compatibility wrapper around wait_on_folio_writeback().

    Turning PageWriteback() into FolioWriteback() eliminates a call to
    compound_head() which saves 8 bytes and 15 bytes in the two functions.
    That is more than offset by adding the wait_on_page_writeback
    compatibility wrapper for a net increase in text of 15 bytes.

    Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    ---
    fs/afs/write.c | 5 +++--
    include/linux/pagemap.h | 3 ++-
    mm/folio-compat.c | 6 ++++++
    mm/page-writeback.c | 48 ++++++++++++++++++++++++++++-------------
    4 files changed, 44 insertions(+), 18 deletions(-)

    diff --git a/fs/afs/write.c b/fs/afs/write.c
    index 106a864b6a93..7af2b57e601b 100644
    --- a/fs/afs/write.c
    +++ b/fs/afs/write.c
    @@ -831,7 +831,8 @@ int afs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
    */
    vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
    {
    - struct page *page = thp_head(vmf->page);
    + struct folio *folio = page_folio(vmf->page);
    + struct page *page = &folio->page;
    struct file *file = vmf->vma->vm_file;
    struct inode *inode = file_inode(file);
    struct afs_vnode *vnode = AFS_FS_I(inode);
    @@ -850,7 +851,7 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
    return VM_FAULT_RETRY;
    #endif

    - if (wait_on_page_writeback_killable(page))
    + if (wait_on_folio_writeback_killable(folio))
    return VM_FAULT_RETRY;

    if (lock_page_killable(page) < 0)
    diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
    index 36c31cfa3e64..2be3a028eb3d 100644
    --- a/include/linux/pagemap.h
    +++ b/include/linux/pagemap.h
    @@ -829,7 +829,8 @@ static inline int wait_on_page_locked_killable(struct page *page)

    int put_and_wait_on_page_locked(struct page *page, int state);
    void wait_on_page_writeback(struct page *page);
    -int wait_on_page_writeback_killable(struct page *page);
    +void wait_on_folio_writeback(struct folio *folio);
    +int wait_on_folio_writeback_killable(struct folio *folio);
    void end_page_writeback(struct page *page);
    void end_folio_writeback(struct folio *folio);
    void wait_for_stable_page(struct page *page);
    diff --git a/mm/folio-compat.c b/mm/folio-compat.c
    index d1a1dfe52589..6aadecc39fba 100644
    --- a/mm/folio-compat.c
    +++ b/mm/folio-compat.c
    @@ -23,3 +23,9 @@ void end_page_writeback(struct page *page)
    return end_folio_writeback(page_folio(page));
    }
    EXPORT_SYMBOL(end_page_writeback);
    +
    +void wait_on_page_writeback(struct page *page)
    +{
    + return wait_on_folio_writeback(page_folio(page));
    +}
    +EXPORT_SYMBOL_GPL(wait_on_page_writeback);
    diff --git a/mm/page-writeback.c b/mm/page-writeback.c
    index 0062d5c57d41..8271f9b24b69 100644
    --- a/mm/page-writeback.c
    +++ b/mm/page-writeback.c
    @@ -2818,33 +2818,51 @@ int __test_set_page_writeback(struct page *page, bool keep_write)
    }
    EXPORT_SYMBOL(__test_set_page_writeback);

    -/*
    - * Wait for a page to complete writeback
    +/**
    + * wait_on_folio_writeback - Wait for a folio to finish writeback.
    + * @folio: The folio to wait for.
    + *
    + * If the folio is currently being written back to storage, wait for the
    + * I/O to complete.
    + *
    + * Context: Sleeps. Must be called in process context and with
    + * no spinlocks held. Caller should hold a reference on the folio.
    + * If the folio is not locked, writeback may start again after writeback
    + * has finished.
    */
    -void wait_on_page_writeback(struct page *page)
    +void wait_on_folio_writeback(struct folio *folio)
    {
    - while (PageWriteback(page)) {
    - trace_wait_on_page_writeback(page, page_mapping(page));
    - wait_on_page_bit(page, PG_writeback);
    + while (FolioWriteback(folio)) {
    + trace_wait_on_page_writeback(&folio->page, folio_mapping(folio));
    + wait_on_page_bit(&folio->page, PG_writeback);
    }
    }
    -EXPORT_SYMBOL_GPL(wait_on_page_writeback);
    +EXPORT_SYMBOL_GPL(wait_on_folio_writeback);

    -/*
    - * Wait for a page to complete writeback. Returns -EINTR if we get a
    - * fatal signal while waiting.
    +/**
    + * wait_on_folio_writeback_killable - Wait for a folio to finish writeback.
    + * @folio: The folio to wait for.
    + *
    + * If the folio is currently being written back to storage, wait for the
    + * I/O to complete or a fatal signal to arrive.
    + *
    + * Context: Sleeps. Must be called in process context and with
    + * no spinlocks held. Caller should hold a reference on the folio.
    + * If the folio is not locked, writeback may start again after writeback
    + * has finished.
    + * Return: 0 on success, -EINTR if we get a fatal signal while waiting.
    */
    -int wait_on_page_writeback_killable(struct page *page)
    +int wait_on_folio_writeback_killable(struct folio *folio)
    {
    - while (PageWriteback(page)) {
    - trace_wait_on_page_writeback(page, page_mapping(page));
    - if (wait_on_page_bit_killable(page, PG_writeback))
    + while (FolioWriteback(folio)) {
    + trace_wait_on_page_writeback(&folio->page, folio_mapping(folio));
    + if (wait_on_page_bit_killable(&folio->page, PG_writeback))
    return -EINTR;
    }

    return 0;
    }
    -EXPORT_SYMBOL_GPL(wait_on_page_writeback_killable);
    +EXPORT_SYMBOL_GPL(wait_on_folio_writeback_killable);

    /**
    * wait_for_stable_page() - wait for writeback to finish, if necessary.
    --
    2.30.2
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