linux-kernel - [PATCH 4.9 026/175] mm/kmemleak.c: make cond

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Date:   Mon, 20 Sep 2021 18:41:15 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Yisheng Xie <xieyisheng1@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 4.9 026/175] mm/kmemleak.c: make cond_resched() rate-limiting more efficient

From: Andrew Morton <akpm@...ux-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@...ux-foundation.org>
Cc: Yisheng Xie <xieyisheng1@...wei.com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Michal Hocko <mhocko@...nel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/kmemleak.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1442,7 +1442,7 @@ 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();
 		}
 	}