[PATCH 09/15] mm/filemap: drop uncached pages when writeback completes

[Jens Axboe <axboe@xxxxxxxxx>]

If the folio is marked as uncached, drop pages when writeback completes.
Intended to be used with RWF_UNCACHED, to avoid needing sync writes for
uncached IO.

Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
 mm/filemap.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index bd698340ef24..efd02b047541 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1600,6 +1600,23 @@ int folio_wait_private_2_killable(struct folio *folio)
 }
 EXPORT_SYMBOL(folio_wait_private_2_killable);
 
+/*
+ * If folio was marked as uncached, then pages should be dropped when writeback
+ * completes. Do that now. If we fail, it's likely because of a big folio -
+ * just reset uncached for that case and latter completions should invalidate.
+ */
+static void folio_end_uncached(struct folio *folio)
+{
+	bool reset = true;
+
+	if (folio_trylock(folio)) {
+		reset = !invalidate_complete_folio2(folio->mapping, folio, 0);
+		folio_unlock(folio);
+	}
+	if (reset)
+		folio_set_uncached(folio);
+}
+
 /**
  * folio_end_writeback - End writeback against a folio.
  * @folio: The folio.
@@ -1610,6 +1627,8 @@ EXPORT_SYMBOL(folio_wait_private_2_killable);
  */
 void folio_end_writeback(struct folio *folio)
 {
+	bool folio_uncached;
+
 	VM_BUG_ON_FOLIO(!folio_test_writeback(folio), folio);
 
 	/*
@@ -1631,9 +1650,13 @@ void folio_end_writeback(struct folio *folio)
 	 * reused before the folio_wake_bit().
 	 */
 	folio_get(folio);
+	folio_uncached = folio_test_clear_uncached(folio);
 	if (__folio_end_writeback(folio))
 		folio_wake_bit(folio, PG_writeback);
 	acct_reclaim_writeback(folio);
+
+	if (folio_uncached)
+		folio_end_uncached(folio);
 	folio_put(folio);
 }
 EXPORT_SYMBOL(folio_end_writeback);
-- 
2.45.2