[PATCH v6 24/27] mm/writeback: Add wait_for_stable_folio

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

Move wait_for_stable_page() into the folio compatibility file.
wait_for_stable_folio() avoids a call to compound_head() and is 14 bytes
smaller than wait_for_stable_page() was.  The net text size grows by 24
bytes as a result of this patch.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 include/linux/pagemap.h |  1 +
 mm/folio-compat.c       |  6 ++++++
 mm/page-writeback.c     | 24 ++++++++++++++----------
 3 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 2be3a028eb3d..001f8ec67ee7 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -834,6 +834,7 @@ 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);
+void wait_for_stable_folio(struct folio *folio);
 
 void page_endio(struct page *page, bool is_write, int err);
 
diff --git a/mm/folio-compat.c b/mm/folio-compat.c
index 6aadecc39fba..335594fe414e 100644
--- a/mm/folio-compat.c
+++ b/mm/folio-compat.c
@@ -29,3 +29,9 @@ void wait_on_page_writeback(struct page *page)
 	return wait_on_folio_writeback(page_folio(page));
 }
 EXPORT_SYMBOL_GPL(wait_on_page_writeback);
+
+void wait_for_stable_page(struct page *page)
+{
+	return wait_for_stable_folio(page_folio(page));
+}
+EXPORT_SYMBOL_GPL(wait_for_stable_page);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 8271f9b24b69..9d55ceec05c0 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2865,17 +2865,21 @@ int wait_on_folio_writeback_killable(struct folio *folio)
 EXPORT_SYMBOL_GPL(wait_on_folio_writeback_killable);
 
 /**
- * wait_for_stable_page() - wait for writeback to finish, if necessary.
- * @page:	The page to wait on.
+ * wait_for_stable_folio() - wait for writeback to finish, if necessary.
+ * @folio: The folio to wait on.
  *
- * This function determines if the given page is related to a backing device
- * that requires page contents to be held stable during writeback.  If so, then
- * it will wait for any pending writeback to complete.
+ * This function determines if the given folio is related to a backing
+ * device that requires folio contents to be held stable during writeback.
+ * If so, then it will wait for any pending writeback 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_for_stable_page(struct page *page)
+void wait_for_stable_folio(struct folio *folio)
 {
-	page = thp_head(page);
-	if (page->mapping->host->i_sb->s_iflags & SB_I_STABLE_WRITES)
-		wait_on_page_writeback(page);
+	if (folio->mapping->host->i_sb->s_iflags & SB_I_STABLE_WRITES)
+		wait_on_folio_writeback(folio);
 }
-EXPORT_SYMBOL_GPL(wait_for_stable_page);
+EXPORT_SYMBOL_GPL(wait_for_stable_folio);
-- 
2.30.2