[RFC PATCH v4 03/12] mm: Refactor folio_clear_dirty_for_io()

[Ojaswin Mujoo <ojaswin@linux.ibm.com>]

Add a new __folio_clear_dirty_for_io() helper which takes an extra
parameter to indicate folio_mkclean() is needed. This is in preparation
of buffered writethrough support where we already do folio_mkclean()
before calling into this function.

Co-developed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
---
 mm/page-writeback.c | 39 +++++++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index eeab25d6ce36..2f8059ab55b9 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2850,20 +2850,12 @@ void __folio_cancel_dirty(struct folio *folio)
 EXPORT_SYMBOL(__folio_cancel_dirty);
 
 /*
- * Clear a folio's dirty flag, while caring for dirty memory accounting.
- * Returns true if the folio was previously dirty.
- *
- * This is for preparing to put the folio under writeout.  We leave
- * the folio tagged as dirty in the xarray so that a concurrent
- * write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk.
- * The ->writepage implementation will run either folio_start_writeback()
- * or folio_mark_dirty(), at which stage we bring the folio's dirty flag
- * and xarray dirty tag back into sync.
- *
- * This incoherency between the folio's dirty flag and xarray tag is
- * unfortunate, but it only exists while the folio is locked.
+ * Internal helper to take care of clearing dirty bit on a folio in preparation
+ * of an IO. For some cases we might not want to do mkclean, eg, if we've
+ * already taken care of it, hence pass the should_mkclean flag to indicate if
+ * its needed.
  */
-bool folio_clear_dirty_for_io(struct folio *folio)
+static bool __folio_clear_dirty_for_io(struct folio *folio, bool should_mkclean)
 {
 	struct address_space *mapping = folio_mapping(folio);
 	bool ret = false;
@@ -2900,7 +2892,7 @@ bool folio_clear_dirty_for_io(struct folio *folio)
 		 * as a serialization point for all the different
 		 * threads doing their things.
 		 */
-		if (folio_mkclean(folio))
+		if (should_mkclean && folio_mkclean(folio))
 			folio_mark_dirty(folio);
 		/*
 		 * We carefully synchronise fault handlers against
@@ -2925,6 +2917,25 @@ bool folio_clear_dirty_for_io(struct folio *folio)
 	}
 	return folio_test_clear_dirty(folio);
 }
+
+/*
+ * Clear a folio's dirty flag, while caring for dirty memory accounting.
+ * Returns true if the folio was previously dirty.
+ *
+ * This is for preparing to put the folio under writeout.  We leave
+ * the folio tagged as dirty in the xarray so that a concurrent
+ * write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk.
+ * The ->writepage implementation will run either folio_start_writeback()
+ * or folio_mark_dirty(), at which stage we bring the folio's dirty flag
+ * and xarray dirty tag back into sync.
+ *
+ * This incoherency between the folio's dirty flag and xarray tag is
+ * unfortunate, but it only exists while the folio is locked.
+ */
+bool folio_clear_dirty_for_io(struct folio *folio)
+{
+	return __folio_clear_dirty_for_io(folio, true);
+}
 EXPORT_SYMBOL(folio_clear_dirty_for_io);
 
 static void wb_inode_writeback_start(struct bdi_writeback *wb)
-- 
2.55.0