mm/vmscan: remove the PageDirty check after MADV_FREE pages are page_ref_freezed

Patch series "Cleanups for vmscan", v2.

This series contains cleanups to remove unneeded return value, misleading
setting and so on.  Also this remove the PageDirty check after MADV_FREE
pages are page_ref_freezed.  More details can be found in the respective
changelogs.

This patch (of 4):

If the MADV_FREE pages are redirtied before they could be reclaimed, put
the pages back to anonymous LRU list by setting SwapBacked flag and the
pages will be reclaimed in normal swapout way.  But as Yu Zhao pointed
out, "The page has only one reference left, which is from the isolation.
After the caller puts the page back on lru and drops the reference, the
page will be freed anyway.  It doesn't matter which lru it goes." So we
don't bother checking PageDirty here.

[Yu Zhao's comment is also quoted in the code.]

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Miaohe Lin <[email protected]>
Reviewed-by: Yu Zhao <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Alex Shi <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Shaohua Li <[email protected]>
Cc: Hillf Danton <[email protected]>
Cc: John Hubbard <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 8 insertions, 5 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2255025f1891..044207d0bb66 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1732,11 +1732,14 @@ retry:
 			/* follow __remove_mapping for reference */
 			if (!page_ref_freeze(page, 1))
 				goto keep_locked;
-			if (PageDirty(page)) {
-				page_ref_unfreeze(page, 1);
-				goto keep_locked;
-			}
-
+			/*
+			 * The page has only one reference left, which is
+			 * from the isolation. After the caller puts the
+			 * page back on lru and drops the reference, the
+			 * page will be freed anyway. It doesn't matter
+			 * which lru it goes. So we don't bother checking
+			 * PageDirty here.
+			 */
 			count_vm_event(PGLAZYFREED);
 			count_memcg_page_event(page, PGLAZYFREED);
 		} else if (!mapping || !__remove_mapping(mapping, page, true,