[PATCH v8 20/31] mm/filemap: Add __folio_lock_async

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

There aren't any actual callers of lock_page_async(), so remove it.
Convert filemap_update_page() to call __folio_lock_async().

__folio_lock_async() is 21 bytes smaller than __lock_page_async(),
but the real savings come from using a folio in filemap_update_page(),
shrinking it from 514 bytes to 403 bytes, saving 111 bytes.  The text
shrinks by 132 bytes in total.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jeff Layton <jlayton@kernel.org>
---
 fs/io_uring.c           |  2 +-
 include/linux/pagemap.h | 17 -----------------
 mm/filemap.c            | 31 ++++++++++++++++---------------
 3 files changed, 17 insertions(+), 33 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index a880edb90d0c..83171c138310 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3158,7 +3158,7 @@ static int io_read_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 }
 
 /*
- * This is our waitqueue callback handler, registered through lock_page_async()
+ * This is our waitqueue callback handler, registered through __folio_lock_async()
  * when we initially tried to do the IO with the iocb armed our waitqueue.
  * This gets called when the page is unlocked, and we generally expect that to
  * happen when the page IO is completed and the page is now uptodate. This will
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 332731ee541a..69c4de9224cd 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -716,7 +716,6 @@ static inline bool wake_page_match(struct wait_page_queue *wait_page,
 
 void __folio_lock(struct folio *folio);
 int __folio_lock_killable(struct folio *folio);
-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);
 void unlock_page(struct page *page);
@@ -773,22 +772,6 @@ static inline int lock_page_killable(struct page *page)
 	return folio_lock_killable(page_folio(page));
 }
 
-/*
- * lock_page_async - Lock the page, unless this would block. If the page
- * is already locked, then queue a callback when the page becomes unlocked.
- * This callback can then retry the operation.
- *
- * Returns 0 if the page is locked successfully, or -EIOCBQUEUED if the page
- * was already locked and the callback defined in 'wait' was queued.
- */
-static inline int lock_page_async(struct page *page,
-				  struct wait_page_queue *wait)
-{
-	if (!trylock_page(page))
-		return __lock_page_async(page, wait);
-	return 0;
-}
-
 /*
  * lock_page_or_retry - Lock the page, unless this would block and the
  * caller indicated that it can handle a retry.
diff --git a/mm/filemap.c b/mm/filemap.c
index 27a86d53dd89..20e1d2c9f3ca 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1595,18 +1595,18 @@ int __folio_lock_killable(struct folio *folio)
 }
 EXPORT_SYMBOL_GPL(__folio_lock_killable);
 
-int __lock_page_async(struct page *page, struct wait_page_queue *wait)
+static int __folio_lock_async(struct folio *folio, struct wait_page_queue *wait)
 {
-	struct wait_queue_head *q = page_waitqueue(page);
+	struct wait_queue_head *q = page_waitqueue(&folio->page);
 	int ret = 0;
 
-	wait->page = page;
+	wait->page = &folio->page;
 	wait->bit_nr = PG_locked;
 
 	spin_lock_irq(&q->lock);
 	__add_wait_queue_entry_tail(q, &wait->wait);
-	SetPageWaiters(page);
-	ret = !trylock_page(page);
+	folio_set_waiters(folio);
+	ret = !folio_trylock(folio);
 	/*
 	 * If we were successful now, we know we're still on the
 	 * waitqueue as we're still under the lock. This means it's
@@ -2359,41 +2359,42 @@ static int filemap_update_page(struct kiocb *iocb,
 		struct address_space *mapping, struct iov_iter *iter,
 		struct page *page)
 {
+	struct folio *folio = page_folio(page);
 	int error;
 
-	if (!trylock_page(page)) {
+	if (!folio_trylock(folio)) {
 		if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO))
 			return -EAGAIN;
 		if (!(iocb->ki_flags & IOCB_WAITQ)) {
-			put_and_wait_on_page_locked(page, TASK_KILLABLE);
+			put_and_wait_on_page_locked(&folio->page, TASK_KILLABLE);
 			return AOP_TRUNCATED_PAGE;
 		}
-		error = __lock_page_async(page, iocb->ki_waitq);
+		error = __folio_lock_async(folio, iocb->ki_waitq);
 		if (error)
 			return error;
 	}
 
-	if (!page->mapping)
+	if (!folio->mapping)
 		goto truncated;
 
 	error = 0;
-	if (filemap_range_uptodate(mapping, iocb->ki_pos, iter, page))
+	if (filemap_range_uptodate(mapping, iocb->ki_pos, iter, &folio->page))
 		goto unlock;
 
 	error = -EAGAIN;
 	if (iocb->ki_flags & (IOCB_NOIO | IOCB_NOWAIT | IOCB_WAITQ))
 		goto unlock;
 
-	error = filemap_read_page(iocb->ki_filp, mapping, page);
+	error = filemap_read_page(iocb->ki_filp, mapping, &folio->page);
 	if (error == AOP_TRUNCATED_PAGE)
-		put_page(page);
+		folio_put(folio);
 	return error;
 truncated:
-	unlock_page(page);
-	put_page(page);
+	folio_unlock(folio);
+	folio_put(folio);
 	return AOP_TRUNCATED_PAGE;
 unlock:
-	unlock_page(page);
+	folio_unlock(folio);
 	return error;
 }
 
-- 
2.30.2