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Date:   Tue, 18 Aug 2020 12:47:04 -0600
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Subject: [PATCH v2 3/3] mm: remove superfluous __ClearPageWaiters()
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>,
        "=?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?=" <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>
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Sender: linux-kernel-owner@vger.kernel.org
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Presumably __ClearPageWaiters() was added to follow the previously
removed __ClearPageActive() pattern.

Only flags that are in PAGE_FLAGS_CHECK_AT_FREE needs to be properly
cleared because otherwise we think there may be some kind of leak.
PG_waiters is not one of those flags and leaving the clearing to
PAGE_FLAGS_CHECK_AT_PREP is more appropriate.

Signed-off-by: Yu Zhao <yuzhao@google.com>
---
 include/linux/page-flags.h | 2 +-
 mm/filemap.c               | 2 ++
 mm/memremap.c              | 2 --
 mm/swap.c                  | 3 ---
 4 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 6be1aa559b1e..dba80a2bdfba 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -318,7 +318,7 @@ static inline int TestClearPage##uname(struct page *page) { return 0; }
 	TESTSETFLAG_FALSE(uname) TESTCLEARFLAG_FALSE(uname)
 
 __PAGEFLAG(Locked, locked, PF_NO_TAIL)
-PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) __CLEARPAGEFLAG(Waiters, waiters, PF_ONLY_HEAD)
+PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD)
 PAGEFLAG(Error, error, PF_NO_TAIL) TESTCLEARFLAG(Error, error, PF_NO_TAIL)
 PAGEFLAG(Referenced, referenced, PF_HEAD)
 	TESTCLEARFLAG(Referenced, referenced, PF_HEAD)
diff --git a/mm/filemap.c b/mm/filemap.c
index 1aaea26556cc..75240c7ef73f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1079,6 +1079,8 @@ static void wake_up_page_bit(struct page *page, int bit_nr)
 		 * other pages on it.
 		 *
 		 * That's okay, it's a rare case. The next waker will clear it.
+		 * Otherwise the bit will be cleared by PAGE_FLAGS_CHECK_AT_PREP
+		 * when the page is being freed.
 		 */
 	}
 	spin_unlock_irqrestore(&q->lock, flags);
diff --git a/mm/memremap.c b/mm/memremap.c
index 3a06eb91cb59..a9d02ffaf9e3 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -451,8 +451,6 @@ void free_devmap_managed_page(struct page *page)
 		return;
 	}
 
-	__ClearPageWaiters(page);
-
 	mem_cgroup_uncharge(page);
 
 	/*
diff --git a/mm/swap.c b/mm/swap.c
index 999a84dbe12c..40bf20a75278 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -90,7 +90,6 @@ static void __page_cache_release(struct page *page)
 		del_page_from_lru_list(page, lruvec, page_off_lru(page));
 		spin_unlock_irqrestore(&pgdat->lru_lock, flags);
 	}
-	__ClearPageWaiters(page);
 }
 
 static void __put_single_page(struct page *page)
@@ -900,8 +899,6 @@ void release_pages(struct page **pages, int nr)
 			del_page_from_lru_list(page, lruvec, page_off_lru(page));
 		}
 
-		__ClearPageWaiters(page);
-
 		list_add(&page->lru, &pages_to_free);
 	}
 	if (locked_pgdat)
-- 
2.28.0.220.ged08abb693-goog