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Wed, 20 Aug 2025 18:06:23 +0800 Message-ID: <43c2ce03-04ac-4da4-a9e2-7f1393939d14@huawei.com> Date: Wed, 20 Aug 2025 18:06:22 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH -next 16/16] mm/damon/core: handle quota->esz overflow issues To: SeongJae Park CC: , , , , , References: <20250813171521.6482-1-sj@kernel.org> From: Quanmin Yan In-Reply-To: <20250813171521.6482-1-sj@kernel.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.176.250] X-ClientProxiedBy: kwepems100002.china.huawei.com (7.221.188.206) To dggpemf200018.china.huawei.com (7.185.36.31) X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: AF10BA0014 X-Stat-Signature: jub8cwyz8ta7fzii1r75a81sj8cywtsm X-Rspam-User: X-HE-Tag: 1755684388-424735 X-HE-Meta: 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 wNm6Sz4u HoY4LD+ghIqaMV6oxDKQUrixT7BaAAjkmuQvX2Bvzjqez3QhMgFPFVbYQkiwkbZyEuL+UXMXqtO9v7jD2qHq2Jrd4izw5YWfvsfFDCY5ixZyWyDmxnl+MnFrPhe0MxWYRpqTRTLli5rqOQZ2+BCwrOYPB2pPYRw6alhsreGKD9WoHEWHT4Hl3ThbHETVfBywqYDEYQm21b9v3z+Y4PogfY+YB5br81do6R8MqY/Jn7lvwVVpfu1YMDUhRpg== 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: Hi SJ, 在 2025/8/14 1:15, SeongJae Park 写道: > On Wed, 13 Aug 2025 13:07:06 +0800 Quanmin Yan wrote: > >> In the original quota enforcement implementation, the traffic >> calculation multiplied A by 1000000 due to time unit conversion, >> making it highly prone to overflow on 32-bit systems: >> >> damos_set_effective_quota >> if (quota->total_charged_ns) >> throughput = quota->total_charged_sz * 1000000 / >> quota->total_charged_ns; >> >> Requiring total_charged_sz to be less than 4GB/1000000 is unreasonable. >> Additionally, when overflow occurs and causes quota->esz to become >> extremely small, the subsequent damos_apply_scheme logic permanently >> sets sz to 0, while quota stop updating, ultimately leading to complete >> functional failure: >> >> damos_apply_scheme >> if (quota->esz && quota->charged_sz + sz > quota->esz) >> sz = ALIGN_DOWN(quota->esz - quota->charged_sz, DAMON_MIN_REGION); >> >> Total charged stats use the unsigned long long data type to reduce >> overflow risk, with data reset capability after overflow occurs. > Thank you for finding this issue! I don't want to change the data type if > possible, though. Could replacing the easily-overflowing throughput > calculation with mult_frac() fix the issue? Thank you for your guidance, it does work effectively. The relevant changes have been included in patch #12 of the v2 series[1]. [1] https://lore.kernel.org/all/20250820080623.3799131-13-yanquanmin1@huawei.com/ Thanks, Quanmin Yan