[RFC PATCH 06/11] mm: Add lock_folio

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

This is like lock_page() but for use by callers who know they have a folio.
Convert __lock_page() to be __lock_folio().  This saves one call to
compound_head() per contended call to lock_page().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/pagemap.h | 21 +++++++++++++++------
 mm/filemap.c            | 29 +++++++++++++++--------------
 2 files changed, 30 insertions(+), 20 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 64ae1bb62765..1d4a1828a434 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -583,7 +583,7 @@ static inline bool wake_page_match(struct wait_page_queue *wait_page,
 	return true;
 }
 
-extern void __lock_page(struct page *page);
+extern void __lock_folio(struct folio *folio);
 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,
@@ -604,13 +604,24 @@ static inline void unlock_page(struct page *page)
 	return unlock_folio(page_folio(page));
 }
 
+static inline bool trylock_folio(struct folio *folio)
+{
+	return likely(!test_and_set_bit_lock(PG_locked, folio_flags(folio)));
+}
+
 /*
  * Return true if the page was successfully locked
  */
 static inline int trylock_page(struct page *page)
 {
-	page = compound_head(page);
-	return (likely(!test_and_set_bit_lock(PG_locked, &page->flags)));
+	return trylock_folio(page_folio(page));
+}
+
+static inline void lock_folio(struct folio *folio)
+{
+	might_sleep();
+	if (!trylock_folio(folio))
+		__lock_folio(folio);
 }
 
 /*
@@ -618,9 +629,7 @@ static inline int trylock_page(struct page *page)
  */
 static inline void lock_page(struct page *page)
 {
-	might_sleep();
-	if (!trylock_page(page))
-		__lock_page(page);
+	lock_folio(page_folio(page));
 }
 
 /*
diff --git a/mm/filemap.c b/mm/filemap.c
index de8372307b33..8e87906f5dd6 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1160,7 +1160,7 @@ static void wake_up_page(struct page *page, int bit)
  */
 enum behavior {
 	EXCLUSIVE,	/* Hold ref to page and take the bit when woken, like
-			 * __lock_page() waiting on then setting PG_locked.
+			 * __lock_folio() waiting on then setting PG_locked.
 			 */
 	SHARED,		/* Hold ref to page and check the bit when woken, like
 			 * wait_on_page_writeback() waiting on PG_writeback.
@@ -1523,17 +1523,16 @@ void page_endio(struct page *page, bool is_write, int err)
 EXPORT_SYMBOL_GPL(page_endio);
 
 /**
- * __lock_page - get a lock on the page, assuming we need to sleep to get it
- * @__page: the page to lock
+ * __lock_folio - Get a lock on the folio, assuming we need to sleep to get it.
+ * @folio: The folio to lock
  */
-void __lock_page(struct page *__page)
+void __lock_folio(struct folio *folio)
 {
-	struct page *page = compound_head(__page);
-	wait_queue_head_t *q = page_waitqueue(page);
-	wait_on_page_bit_common(q, page, PG_locked, TASK_UNINTERRUPTIBLE,
+	wait_queue_head_t *q = page_waitqueue(&folio->page);
+	wait_on_page_bit_common(q, &folio->page, PG_locked, TASK_UNINTERRUPTIBLE,
 				EXCLUSIVE);
 }
-EXPORT_SYMBOL(__lock_page);
+EXPORT_SYMBOL(__lock_folio);
 
 int __lock_page_killable(struct page *__page)
 {
@@ -1587,10 +1586,10 @@ int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
 			return 0;
 		}
 	} else {
-		__lock_page(page);
+		__lock_folio(page_folio(page));
 	}
-	return 1;
 
+	return 1;
 }
 
 /**
@@ -2764,7 +2763,9 @@ loff_t mapping_seek_hole_data(struct address_space *mapping, loff_t start,
 static int lock_page_maybe_drop_mmap(struct vm_fault *vmf, struct page *page,
 				     struct file **fpin)
 {
-	if (trylock_page(page))
+	struct folio *folio = page_folio(page);
+
+	if (trylock_folio(folio))
 		return 1;
 
 	/*
@@ -2777,7 +2778,7 @@ static int lock_page_maybe_drop_mmap(struct vm_fault *vmf, struct page *page,
 
 	*fpin = maybe_unlock_mmap_for_io(vmf, *fpin);
 	if (vmf->flags & FAULT_FLAG_KILLABLE) {
-		if (__lock_page_killable(page)) {
+		if (__lock_page_killable(&folio->page)) {
 			/*
 			 * We didn't have the right flags to drop the mmap_lock,
 			 * but all fault_handlers only check for fatal signals
@@ -2789,11 +2790,11 @@ static int lock_page_maybe_drop_mmap(struct vm_fault *vmf, struct page *page,
 			return 0;
 		}
 	} else
-		__lock_page(page);
+		__lock_folio(folio);
+
 	return 1;
 }
 
-
 /*
  * Synchronous readahead happens when we don't even find a page in the page
  * cache at all.  We don't want to perform IO under the mmap sem, so if we have
-- 
2.29.2