linux-kernel - [RFC PATCH mm-next v2 12/12] mm/damon/core: prevent unnecessary overflow in damos_set_effective

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Message-ID: <20250820080623.3799131-13-yanquanmin1@huawei.com>
Date: Wed, 20 Aug 2025 16:06:22 +0800
From: Quanmin Yan <yanquanmin1@...wei.com>
To: <sj@...nel.org>
CC: <akpm@...ux-foundation.org>, <damon@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<yanquanmin1@...wei.com>, <wangkefeng.wang@...wei.com>, <zuoze1@...wei.com>
Subject: [RFC PATCH mm-next v2 12/12] mm/damon/core: prevent unnecessary overflow in damos_set_effective_quota()

On 32-bit systems, the throughput calculation in function
damos_set_effective_quota() is prone to unnecessary
multiplication overflow. Using mult_frac() to fix it.

Signed-off-by: Quanmin Yan <yanquanmin1@...wei.com>
---
 mm/damon/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 980e271e42e9..38b5f842ef30 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2102,8 +2102,8 @@ static void damos_set_effective_quota(struct damos_quota *quota)
 
 	if (quota->ms) {
 		if (quota->total_charged_ns)
-			throughput = quota->total_charged_sz * 1000000 /
-				quota->total_charged_ns;
+			throughput = mult_frac(quota->total_charged_sz, 1000000,
+							quota->total_charged_ns);
 		else
 			throughput = PAGE_SIZE * 1024;
 		esz = min(throughput * quota->ms, esz);
-- 
2.43.0