[PATCH v5 24/27] mm/filemap: Convert wait_on_page_bit to wait_on_folio_bit

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

We must always wait on the folio, otherwise we won't be woken up.

This commit shrinks the kernel by 691 bytes, mostly due to moving
the page waitqueue lookup into wait_on_folio_bit_common().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/netfs.h   |  2 +-
 include/linux/pagemap.h | 10 ++++----
 mm/filemap.c            | 56 ++++++++++++++++++-----------------------
 mm/page-writeback.c     |  4 +--
 4 files changed, 33 insertions(+), 39 deletions(-)

diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 9d3fbed4e30a..f44142dca767 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -54,7 +54,7 @@ static inline void unlock_page_fscache(struct page *page)
 static inline void wait_on_page_fscache(struct page *page)
 {
 	if (PageFsCache(page))
-		wait_on_page_bit(compound_head(page), PG_fscache);
+		wait_on_folio_bit(page_folio(page), PG_fscache);
 }
 
 enum netfs_read_source {
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index c92782b77d98..7ddaabbd1ddb 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -770,11 +770,11 @@ static inline int lock_page_or_retry(struct page *page, struct mm_struct *mm,
 }
 
 /*
- * This is exported only for wait_on_page_locked/wait_on_page_writeback, etc.,
+ * This is exported only for wait_on_folio_locked/wait_on_folio_writeback, etc.,
  * and should not be used directly.
  */
-extern void wait_on_page_bit(struct page *page, int bit_nr);
-extern int wait_on_page_bit_killable(struct page *page, int bit_nr);
+extern void wait_on_folio_bit(struct folio *folio, int bit_nr);
+extern int wait_on_folio_bit_killable(struct folio *folio, int bit_nr);
 
 /* 
  * Wait for a folio to be unlocked.
@@ -786,14 +786,14 @@ extern int wait_on_page_bit_killable(struct page *page, int bit_nr);
 static inline void wait_on_folio_locked(struct folio *folio)
 {
 	if (FolioLocked(folio))
-		wait_on_page_bit(&folio->page, PG_locked);
+		wait_on_folio_bit(folio, PG_locked);
 }
 
 static inline int wait_on_folio_locked_killable(struct folio *folio)
 {
 	if (!FolioLocked(folio))
 		return 0;
-	return wait_on_page_bit_killable(&folio->page, PG_locked);
+	return wait_on_folio_bit_killable(folio, PG_locked);
 }
 
 static inline void wait_on_page_locked(struct page *page)
diff --git a/mm/filemap.c b/mm/filemap.c
index dc7deb8c36ee..f8746c149562 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1102,7 +1102,7 @@ static int wake_page_function(wait_queue_entry_t *wait, unsigned mode, int sync,
 	 *
 	 * So update the flags atomically, and wake up the waiter
 	 * afterwards to avoid any races. This store-release pairs
-	 * with the load-acquire in wait_on_page_bit_common().
+	 * with the load-acquire in wait_on_folio_bit_common().
 	 */
 	smp_store_release(&wait->flags, flags | WQ_FLAG_WOKEN);
 	wake_up_state(wait->private, mode);
@@ -1183,7 +1183,7 @@ static void wake_up_folio(struct folio *folio, int bit)
 }
 
 /*
- * A choice of three behaviors for wait_on_page_bit_common():
+ * A choice of three behaviors for wait_on_folio_bit_common():
  */
 enum behavior {
 	EXCLUSIVE,	/* Hold ref to page and take the bit when woken, like
@@ -1217,9 +1217,10 @@ static inline bool trylock_page_bit_common(struct page *page, int bit_nr,
 /* How many times do we accept lock stealing from under a waiter? */
 int sysctl_page_lock_unfairness = 5;
 
-static inline int wait_on_page_bit_common(wait_queue_head_t *q,
-	struct page *page, int bit_nr, int state, enum behavior behavior)
+static inline int wait_on_folio_bit_common(struct folio *folio, int bit_nr,
+		int state, enum behavior behavior)
 {
+	wait_queue_head_t *q = page_waitqueue(&folio->page);
 	int unfairness = sysctl_page_lock_unfairness;
 	struct wait_page_queue wait_page;
 	wait_queue_entry_t *wait = &wait_page.wait;
@@ -1228,8 +1229,8 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 	unsigned long pflags;
 
 	if (bit_nr == PG_locked &&
-	    !PageUptodate(page) && PageWorkingset(page)) {
-		if (!PageSwapBacked(page)) {
+	    !FolioUptodate(folio) && FolioWorkingset(folio)) {
+		if (!FolioSwapBacked(folio)) {
 			delayacct_thrashing_start();
 			delayacct = true;
 		}
@@ -1239,7 +1240,7 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 
 	init_wait(wait);
 	wait->func = wake_page_function;
-	wait_page.page = page;
+	wait_page.page = &folio->page;
 	wait_page.bit_nr = bit_nr;
 
 repeat:
@@ -1254,7 +1255,7 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 	 * Do one last check whether we can get the
 	 * page bit synchronously.
 	 *
-	 * Do the SetPageWaiters() marking before that
+	 * Do the SetFolioWaiters() marking before that
 	 * to let any waker we _just_ missed know they
 	 * need to wake us up (otherwise they'll never
 	 * even go to the slow case that looks at the
@@ -1265,8 +1266,8 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 	 * lock to avoid races.
 	 */
 	spin_lock_irq(&q->lock);
-	SetPageWaiters(page);
-	if (!trylock_page_bit_common(page, bit_nr, wait))
+	SetFolioWaiters(folio);
+	if (!trylock_page_bit_common(&folio->page, bit_nr, wait))
 		__add_wait_queue_entry_tail(q, wait);
 	spin_unlock_irq(&q->lock);
 
@@ -1276,10 +1277,10 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 	 * see whether the page bit testing has already
 	 * been done by the wake function.
 	 *
-	 * We can drop our reference to the page.
+	 * We can drop our reference to the folio.
 	 */
 	if (behavior == DROP)
-		put_page(page);
+		put_folio(folio);
 
 	/*
 	 * Note that until the "finish_wait()", or until
@@ -1316,7 +1317,7 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 		 *
 		 * And if that fails, we'll have to retry this all.
 		 */
-		if (unlikely(test_and_set_bit(bit_nr, &page->flags)))
+		if (unlikely(test_and_set_bit(bit_nr, folio_flags(folio, 0))))
 			goto repeat;
 
 		wait->flags |= WQ_FLAG_DONE;
@@ -1325,7 +1326,7 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 
 	/*
 	 * If a signal happened, this 'finish_wait()' may remove the last
-	 * waiter from the wait-queues, but the PageWaiters bit will remain
+	 * waiter from the wait-queues, but the FolioWaiters bit will remain
 	 * set. That's ok. The next wakeup will take care of it, and trying
 	 * to do it here would be difficult and prone to races.
 	 */
@@ -1356,19 +1357,17 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 	return wait->flags & WQ_FLAG_WOKEN ? 0 : -EINTR;
 }
 
-void wait_on_page_bit(struct page *page, int bit_nr)
+void wait_on_folio_bit(struct folio *folio, int bit_nr)
 {
-	wait_queue_head_t *q = page_waitqueue(page);
-	wait_on_page_bit_common(q, page, bit_nr, TASK_UNINTERRUPTIBLE, SHARED);
+	wait_on_folio_bit_common(folio, bit_nr, TASK_UNINTERRUPTIBLE, SHARED);
 }
-EXPORT_SYMBOL(wait_on_page_bit);
+EXPORT_SYMBOL(wait_on_folio_bit);
 
-int wait_on_page_bit_killable(struct page *page, int bit_nr)
+int wait_on_folio_bit_killable(struct folio *folio, int bit_nr)
 {
-	wait_queue_head_t *q = page_waitqueue(page);
-	return wait_on_page_bit_common(q, page, bit_nr, TASK_KILLABLE, SHARED);
+	return wait_on_folio_bit_common(folio, bit_nr, TASK_KILLABLE, SHARED);
 }
-EXPORT_SYMBOL(wait_on_page_bit_killable);
+EXPORT_SYMBOL(wait_on_folio_bit_killable);
 
 /**
  * put_and_wait_on_page_locked - Drop a reference and wait for it to be unlocked
@@ -1385,11 +1384,8 @@ EXPORT_SYMBOL(wait_on_page_bit_killable);
  */
 int put_and_wait_on_page_locked(struct page *page, int state)
 {
-	wait_queue_head_t *q;
-
-	page = compound_head(page);
-	q = page_waitqueue(page);
-	return wait_on_page_bit_common(q, page, PG_locked, state, DROP);
+	return wait_on_folio_bit_common(page_folio(page), PG_locked, state,
+			DROP);
 }
 
 /**
@@ -1540,16 +1536,14 @@ EXPORT_SYMBOL_GPL(page_endio);
  */
 void __lock_folio(struct folio *folio)
 {
-	wait_queue_head_t *q = page_waitqueue(&folio->page);
-	wait_on_page_bit_common(q, &folio->page, PG_locked, TASK_UNINTERRUPTIBLE,
+	wait_on_folio_bit_common(folio, PG_locked, TASK_UNINTERRUPTIBLE,
 				EXCLUSIVE);
 }
 EXPORT_SYMBOL(__lock_folio);
 
 int __lock_folio_killable(struct folio *folio)
 {
-	wait_queue_head_t *q = page_waitqueue(&folio->page);
-	return wait_on_page_bit_common(q, &folio->page, PG_locked, TASK_KILLABLE,
+	return wait_on_folio_bit_common(folio, PG_locked, TASK_KILLABLE,
 					EXCLUSIVE);
 }
 EXPORT_SYMBOL_GPL(__lock_folio_killable);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index c222f88cf06b..b29737cd8049 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2832,7 +2832,7 @@ void wait_on_folio_writeback(struct folio *folio)
 {
 	while (FolioWriteback(folio)) {
 		trace_wait_on_page_writeback(&folio->page, folio_mapping(folio));
-		wait_on_page_bit(&folio->page, PG_writeback);
+		wait_on_folio_bit(folio, PG_writeback);
 	}
 }
 EXPORT_SYMBOL_GPL(wait_on_folio_writeback);
@@ -2853,7 +2853,7 @@ int wait_on_folio_writeback_killable(struct folio *folio)
 {
 	while (FolioWriteback(folio)) {
 		trace_wait_on_page_writeback(&folio->page, folio_mapping(folio));
-		if (wait_on_page_bit_killable(&folio->page, PG_writeback))
+		if (wait_on_folio_bit_killable(folio, PG_writeback))
 			return -EINTR;
 	}
 
-- 
2.30.2