[PATCH v8 19/27] mm/filemap: Add folio_lock_killable

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

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

__folio_lock_killable() is 20 bytes smaller than __lock_page_killable()
was.  lock_page_maybe_drop_mmap() shrinks by 68 bytes and
__lock_page_or_retry() shrinks by 66 bytes.  That's a total of 154 bytes
of text saved.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
 include/linux/pagemap.h | 15 ++++++++++-----
 mm/filemap.c            | 17 +++++++++--------
 2 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index ff81be103539..332731ee541a 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -715,7 +715,7 @@ static inline bool wake_page_match(struct wait_page_queue *wait_page,
 }
 
 void __folio_lock(struct folio *folio);
-extern int __lock_page_killable(struct page *page);
+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);
@@ -755,6 +755,14 @@ static inline void lock_page(struct page *page)
 		__folio_lock(folio);
 }
 
+static inline int folio_lock_killable(struct folio *folio)
+{
+	might_sleep();
+	if (!folio_trylock(folio))
+		return __folio_lock_killable(folio);
+	return 0;
+}
+
 /*
  * lock_page_killable is like lock_page but can be interrupted by fatal
  * signals.  It returns 0 if it locked the page and -EINTR if it was
@@ -762,10 +770,7 @@ static inline void lock_page(struct page *page)
  */
 static inline int lock_page_killable(struct page *page)
 {
-	might_sleep();
-	if (!trylock_page(page))
-		return __lock_page_killable(page);
-	return 0;
+	return folio_lock_killable(page_folio(page));
 }
 
 /*
diff --git a/mm/filemap.c b/mm/filemap.c
index 6935b068856f..27a86d53dd89 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1587,14 +1587,13 @@ void __folio_lock(struct folio *folio)
 }
 EXPORT_SYMBOL(__folio_lock);
 
-int __lock_page_killable(struct page *__page)
+int __folio_lock_killable(struct folio *folio)
 {
-	struct page *page = compound_head(__page);
-	wait_queue_head_t *q = page_waitqueue(page);
-	return wait_on_page_bit_common(q, page, PG_locked, TASK_KILLABLE,
+	wait_queue_head_t *q = page_waitqueue(&folio->page);
+	return wait_on_page_bit_common(q, &folio->page, PG_locked, TASK_KILLABLE,
 					EXCLUSIVE);
 }
-EXPORT_SYMBOL_GPL(__lock_page_killable);
+EXPORT_SYMBOL_GPL(__folio_lock_killable);
 
 int __lock_page_async(struct page *page, struct wait_page_queue *wait)
 {
@@ -1636,6 +1635,8 @@ int __lock_page_async(struct page *page, struct wait_page_queue *wait)
 int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
 			 unsigned int flags)
 {
+	struct folio *folio = page_folio(page);
+
 	if (fault_flag_allow_retry_first(flags)) {
 		/*
 		 * CAUTION! In this case, mmap_lock is not released
@@ -1654,13 +1655,13 @@ int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
 	if (flags & FAULT_FLAG_KILLABLE) {
 		int ret;
 
-		ret = __lock_page_killable(page);
+		ret = __folio_lock_killable(folio);
 		if (ret) {
 			mmap_read_unlock(mm);
 			return 0;
 		}
 	} else {
-		__folio_lock(page_folio(page));
+		__folio_lock(folio);
 	}
 
 	return 1;
@@ -2829,7 +2830,7 @@ 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(&folio->page)) {
+		if (__folio_lock_killable(folio)) {
 			/*
 			 * We didn't have the right flags to drop the mmap_lock,
 			 * but all fault_handlers only check for fatal signals
-- 
2.30.2