From: Barry Song <v-songbaohua@xxxxxxxx>
The optimization of list_empty(&folio->_deferred_list) aimed to prevent
increasing the PTL duration when a large folio is partially unmapped,
for example, from subpage 0 to subpage (nr - 2).
But Ryan's commit 5ed890ce5147 ("mm: vmscan: avoid split during
shrink_folio_list()") actually splits this kind of large folios. This
makes the "optimization" useless.
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
---
-v1
* I remember David and Ryan once suggested that this check could be dropped
while the patch was being pulled into mm-unstable. However, for some reason,
I forgot to request squashing this change.
mm/vmscan.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3d4c681c6d40..0761f91b407f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1291,7 +1291,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
* try_to_unmap acquire PTL from the first PTE,
* eliminating the influence of temporary PTE values.
*/
- if (folio_test_large(folio) && list_empty(&folio->_deferred_list))
+ if (folio_test_large(folio))
flags |= TTU_SYNC;
try_to_unmap(folio, flags);
--
2.34.1
