[RFC PATCH v1 06/10] mm: add __folio_clear_dirty_for_io() helper

[Joanne Koong <joannelkoong@gmail.com>]

Add __folio_clear_dirty_for_io() which takes in an arg for whether the
folio and wb stats should be updated as part of the call or not.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 mm/page-writeback.c | 47 +++++++++++++++++++++++++++------------------
 1 file changed, 28 insertions(+), 19 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index a3805988f3ad..77a46bf8052f 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2927,21 +2927,7 @@ 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.
- */
-bool folio_clear_dirty_for_io(struct folio *folio)
+static bool __folio_clear_dirty_for_io(struct folio *folio, bool update_stats)
 {
 	struct address_space *mapping = folio_mapping(folio);
 	bool ret = false;
@@ -2990,10 +2976,14 @@ bool folio_clear_dirty_for_io(struct folio *folio)
 		 */
 		wb = unlocked_inode_to_wb_begin(inode, &cookie);
 		if (folio_test_clear_dirty(folio)) {
-			long nr = folio_nr_pages(folio);
-			lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
-			zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
-			wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
+			if (update_stats) {
+				long nr = folio_nr_pages(folio);
+				lruvec_stat_mod_folio(folio, NR_FILE_DIRTY,
+						      -nr);
+				zone_stat_mod_folio(folio,
+						    NR_ZONE_WRITE_PENDING, -nr);
+				wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
+			}
 			ret = true;
 		}
 		unlocked_inode_to_wb_end(inode, &cookie);
@@ -3001,6 +2991,25 @@ 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)
-- 
2.47.3