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From:   Liu Shixin <liushixin2@huawei.com>
To:     Andrew Morton <akpm@linux-foundation.org>
CC:     <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
        Liu Shixin <liushixin2@huawei.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>
Subject: [PATCH] mm/huge_memory: prevent THP_ZERO_PAGE_ALLOC increased twice
Date:   Mon, 5 Sep 2022 21:38:13 +0800
Message-ID: <20220905133813.2253703-1-liushixin2@huawei.com>
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If two or more threads call get_huge_zero_page concurrently, THP_ZERO_PAGE_ALLOC
may increased two or more times. But actually, this should only count
as once since the extra zero pages has been freed.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 88d98241a635..5c83a424803a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -163,7 +163,6 @@ static bool get_huge_zero_page(void)
 		count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
 		return false;
 	}
-	count_vm_event(THP_ZERO_PAGE_ALLOC);
 	preempt_disable();
 	if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
 		preempt_enable();
@@ -175,6 +174,7 @@ static bool get_huge_zero_page(void)
 	/* We take additional reference here. It will be put back by shrinker */
 	atomic_set(&huge_zero_refcount, 2);
 	preempt_enable();
+	count_vm_event(THP_ZERO_PAGE_ALLOC);
 	return true;
 }
 
-- 
2.25.1