linux-kernel - [PATCH 2/3] mm: remove superfluous _

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Message-Id: <20200812040550.2708444-1-yuzhao@google.com>
Date:   Tue, 11 Aug 2020 22:05:50 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Huang Ying <ying.huang@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>, Qian Cai <cai@....pw>,
        Mel Gorman <mgorman@...e.de>,
        Nicholas Piggin <npiggin@...il.com>,
        "Jérôme Glisse" <jglisse@...hat.com>,
        Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Yu Zhao <yuzhao@...gle.com>
Subject: [PATCH 2/3] mm: remove superfluous __ClearPageActive()

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 can't call
SetPageActive() on a page that doesn't have any reference left.
Therefore, the race is impossible, not 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@...gle.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 de257c0a89b1..1f223a02549d 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -898,8 +898,6 @@ 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);
-- 
2.28.0.236.gb10cc79966-goog