mm/vmscan: drop checking if _deferred_list is empty before using TTU_SYNC

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.

Additionally, the list_empty() technically required a data_race()
annotation.

Link: https://lkml.kernel.org/r/20240629234155.53524-1-21cnbao@gmail.com
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3d4c681c6d40ab68b429d8d277d0a6964c81c975..0761f91b407f35029e85e2e69c1408df15efcf69 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1291,7 +1291,7 @@ retry:
                         * 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);