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Thu, 21 Aug 2025 21:09:38 +0800 From: Quanmin Yan To: CC: , , , , , , , Subject: [PATCH] mm/damon/core: prevent unnecessary overflow in damos_set_effective_quota() Date: Thu, 21 Aug 2025 20:55:55 +0800 Message-ID: <20250821125555.3020951-1-yanquanmin1@huawei.com> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.50.85.135] X-ClientProxiedBy: kwepems100002.china.huawei.com (7.221.188.206) To dggpemf200018.china.huawei.com (7.185.36.31) X-Rspamd-Queue-Id: 62E10C000D X-Rspam-User: X-Stat-Signature: pmwskfczu97txx5km9psrzm3xsgqz6rm X-Rspamd-Server: rspam09 X-HE-Tag: 1755781783-207495 X-HE-Meta: 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 2sraByq5 dH/I5fVN9BnXLEpWBQpsBhNVeLFcIUdXUoPExWeDUjZzT1SP8dgZ/eg2zSc9Kw/q+cyEtK3HuO7KcG1qoGNSrBETQKHaLqCM0lHhyq2WTkck+VUkg+fL0SuOzXliEDhpP/uoRLr+Rv29YVkbpKML0H61F3yPdXKu6zZS89GHezMyN2948zYJ/AR34BSOkcMEmPlELxRewkissCh9bDH5SL4+ptZtgDNj64J+TPlx4BJG+Nm+XD1xMqig8zg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. Andrew Paniakin also recently found and privately reported this issue, on 64 bit systems. This can also happen on 64-bit systems, once the charged size exceeds ~17 TiB. On systems running for long time in production, this issue can actually happen. More specifically, when a DAMOS scheme having the time quota run for longtime, throughput calculation can overflow and set esz too small. As a result, speed of the scheme get unexpectedly slow. Fixes: 1cd243030059 ("mm/damon/schemes: implement time quota") Cc: # 5.16.x Signed-off-by: Quanmin Yan Reported-by: Andrew Paniakin Closes: N/A # privately reported --- 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 831a9afc6cf6..fe1c19307ddd 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2103,8 +2103,8 @@ 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