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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Yisheng Xie <xieyisheng1@huawei.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: [PATCH 4.14 019/217] mm/kmemleak.c: make cond_resched() rate-limiting more efficient
Date:   Mon, 20 Sep 2021 18:40:40 +0200
Message-Id: <20210920163925.258901280@linuxfoundation.org>
In-Reply-To: <20210920163924.591371269@linuxfoundation.org>
References: <20210920163924.591371269@linuxfoundation.org>
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From: Andrew Morton <akpm@linux-foundation.org>

commit 13ab183d138f607d885e995d625e58d47678bf97 upstream.

Commit bde5f6bc68db ("kmemleak: add scheduling point to
kmemleak_scan()") tries to rate-limit the frequency of cond_resched()
calls, but does it in a way which might incur an expensive division
operation in the inner loop.  Simplify this.

Fixes: bde5f6bc68db5 ("kmemleak: add scheduling point to kmemleak_scan()")
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Yisheng Xie <xieyisheng1@huawei.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 mm/kmemleak.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1520,7 +1520,7 @@ static void kmemleak_scan(void)
 			if (page_count(page) == 0)
 				continue;
 			scan_block(page, page + 1, NULL);
-			if (!(pfn % (MAX_SCAN_SIZE / sizeof(*page))))
+			if (!(pfn & 63))
 				cond_resched();
 		}
 	}