[PATCH v2 2/3] mm: remove superfluous __ClearPageActive()

From: Yu Zhao <yuzhao@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Alexander Duyck" <alexander.h.duyck@linux.intel.com>,
	"Huang Ying" <ying.huang@intel.com>,
	"David Hildenbrand" <david@redhat.com>,
	"Michal Hocko" <mhocko@suse.com>,
	"Yang Shi" <yang.shi@linux.alibaba.com>, "Qian Cai" <cai@lca.pw>,
	"Mel Gorman" <mgorman@suse.de>,
	"Nicholas Piggin" <npiggin@gmail.com>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Hugh Dickins" <hughd@google.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	"Joonsoo Kim" <iamjoonsoo.kim@lge.com>,
	"Yu Zhao" <yuzhao@google.com>
Subject: [PATCH v2 2/3] mm: remove superfluous __ClearPageActive()
Date: Tue, 18 Aug 2020 12:47:03 -0600	[thread overview]
Message-ID: <20200818184704.3625199-2-yuzhao@google.com> (raw)
In-Reply-To: <20200818184704.3625199-1-yuzhao@google.com>

To activate a page, mark_page_accessed() always holds a reference
on it. It either gets a new reference when adding a page to
lru_pvecs.activate_page or reuses an existing one it previously
got when it added a page to lru_pvecs.lru_add. So it doesn't call
SetPageActive() on a page that doesn't have any reference left.
Therefore, the race is impossible these days (I didn't brother to
dig into its history).

For other paths, namely reclaim and migration, a reference count is
always held while calling SetPageActive() on a page.

SetPageSlabPfmemalloc() also uses SetPageActive(), but it's irrelevant
to LRU pages.

Signed-off-by: Yu Zhao <yuzhao@google.com>
---
 mm/memremap.c | 2 --
 mm/swap.c     | 2 --
 2 files changed, 4 deletions(-)

diff --git a/mm/memremap.c b/mm/memremap.c
index 03e38b7a38f1..3a06eb91cb59 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -451,8 +451,6 @@ void free_devmap_managed_page(struct page *page)
 		return;
 	}
 
-	/* Clear Active bit in case of parallel mark_page_accessed */
-	__ClearPageActive(page);
 	__ClearPageWaiters(page);
 
 	mem_cgroup_uncharge(page);
diff --git a/mm/swap.c b/mm/swap.c
index 25c4043491b3..999a84dbe12c 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -900,8 +900,6 @@ void release_pages(struct page **pages, int nr)
 			del_page_from_lru_list(page, lruvec, page_off_lru(page));
 		}
 
-		/* Clear Active bit in case of parallel mark_page_accessed */
-		__ClearPageActive(page);
 		__ClearPageWaiters(page);
 
 		list_add(&page->lru, &pages_to_free);
-- 
2.28.0.220.ged08abb693-goog

