From: Barry Song <v-songbaohua@oppo.com>
Date: Sat, 29 Jun 2024 23:41:55 +0000 (+1200)
Subject: mm/vmscan: drop checking if _deferred_list is empty before using TTU_SYNC
X-Git-Tag: v6.11-rc1~85^2~78
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e5a119c4a6835a53f93fcfba6c177daef58467e3;p=thirdparty%2Fkernel%2Flinux.git

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 3d4c681c6d40a..0761f91b407f3 100644
--- 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);