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/20210717065911.61497-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20210717065911.61497-2-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Yu Zhao <yuzhao@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 874efeeca4e4e1252790b2853ef5692a39660e7f..776f45692e6856bc8f184573dadcffc18281a416 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1739,11 +1739,14 @@ 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,