linux-kernel - [PATCH 3/3] mm/page-writeback.c: improve arithmetic divisions

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Date:   Thu,  2 Jan 2020 16:14:42 +0800
From:   Wen Yang <wenyang@...ux.alibaba.com>
To:     Andrew Morton <akpm@...ux-foundation.org>, Qian Cai <cai@....pw>
Cc:     xlpang@...ux.alibaba.com, Wen Yang <wenyang@...ux.alibaba.com>,
        Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] mm/page-writeback.c: improve arithmetic divisions

Use div64_ul() instead of do_div() if the divisor is unsigned long,
to avoid truncation to 32-bit on 64-bit platforms.

Signed-off-by: Wen Yang <wenyang@...ux.alibaba.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Qian Cai <cai@....pw>
Cc: Tejun Heo <tj@...nel.org>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
---
 mm/page-writeback.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index c74c6bd..2caf780 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1102,7 +1102,7 @@ static void wb_update_write_bandwidth(struct bdi_writeback *wb,
 	bw = written - min(written, wb->written_stamp);
 	bw *= HZ;
 	if (unlikely(elapsed > period)) {
-		do_div(bw, elapsed);
+		bw = div64_ul(bw, elapsed);
 		avg = bw;
 		goto out;
 	}
-- 
1.8.3.1