[PATCH v4 18/25] mm/page-writeback: Add wait_on_folio_writeback

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

This eliminates a call to compound_head() by turning PageWriteback()
into FolioWriteback(), which saves 8 bytes.  That is more than offset
by adding the wait_on_page_writeback compatibility wrapper for a net
increase in text of 30 bytes.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/pagemap.h |  1 +
 mm/folio-compat.c       |  6 ++++++
 mm/page-writeback.c     | 21 ++++++++++++++-------
 3 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index c53743f24550..7d797847633c 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -763,6 +763,7 @@ static inline int wait_on_page_locked_killable(struct page *page)
 
 int put_and_wait_on_page_locked(struct page *page, int state);
 void wait_on_page_writeback(struct page *page);
+void wait_on_folio_writeback(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);
diff --git a/mm/folio-compat.c b/mm/folio-compat.c
index d1a1dfe52589..6aadecc39fba 100644
--- a/mm/folio-compat.c
+++ b/mm/folio-compat.c
@@ -23,3 +23,9 @@ void end_page_writeback(struct page *page)
 	return end_folio_writeback(page_folio(page));
 }
 EXPORT_SYMBOL(end_page_writeback);
+
+void wait_on_page_writeback(struct page *page)
+{
+	return wait_on_folio_writeback(page_folio(page));
+}
+EXPORT_SYMBOL_GPL(wait_on_page_writeback);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index eb34d204d4ee..968579452ea4 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2821,17 +2821,24 @@ int __test_set_page_writeback(struct page *page, bool keep_write)
 }
 EXPORT_SYMBOL(__test_set_page_writeback);
 
-/*
- * Wait for a page to complete writeback
+/**
+ * wait_on_folio_writeback - Wait for a folio to complete writeback.
+ * @folio: The folio to wait for.
+ *
+ * If the folio is currently being written back to storage, waits for the
+ * I/O to complete.
+ *
+ * Context: Sleeps; must be called in process context and with no spinlocks
+ * held.
  */
-void wait_on_page_writeback(struct page *page)
+void wait_on_folio_writeback(struct folio *folio)
 {
-	while (PageWriteback(page)) {
-		trace_wait_on_page_writeback(page, page_mapping(page));
-		wait_on_page_bit(page, PG_writeback);
+	while (FolioWriteback(folio)) {
+		trace_wait_on_page_writeback(&folio->page, folio_mapping(folio));
+		wait_on_page_bit(&folio->page, PG_writeback);
 	}
 }
-EXPORT_SYMBOL_GPL(wait_on_page_writeback);
+EXPORT_SYMBOL_GPL(wait_on_folio_writeback);
 
 /**
  * wait_for_stable_page() - wait for writeback to finish, if necessary.
-- 
2.30.0