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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1rFRNK-00HZi9-G4; Tue, 19 Dec 2023 04:06:34 +0000 Date: Tue, 19 Dec 2023 04:06:34 +0000 From: Matthew Wilcox To: Jingbo Xu Cc: shr@devkernel.io, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, joseph.qi@linux.alibaba.com, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org Subject: Re: [PATCH v2 2/2] mm: fix arithmetic for max_prop_frac when setting max_ratio Message-ID: References: <20231219024246.65654-1-jefflexu@linux.alibaba.com> <20231219024246.65654-3-jefflexu@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231219024246.65654-3-jefflexu@linux.alibaba.com> X-Rspamd-Queue-Id: 7810514000D X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: kqj1pmyzt99o8he9zirie4hc13918pad X-HE-Tag: 1702958806-994479 X-HE-Meta: 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 jgEHmaAx PfGogAUlSvCr2OeW+alVrQjd9myu042OX5OSupsjYKdixGHKME8UA/LAnblprSHPKg9rvjokcMf2UyMhpfxjdsuh7SV7UjqmhZX/ffyO61KPnapbkRKTd9+ezoQvEDUIcvwjN6Q5bv7lJdI2KbXROzJsKQ4vOrCs1TMIvSWpe5H74pPd5vGE9u13zwA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.001195, 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 Tue, Dec 19, 2023 at 10:42:46AM +0800, Jingbo Xu wrote: > } else { > bdi->max_ratio = max_ratio; > - bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100; > + bdi->max_prop_frac = div64_u64(FPROP_FRAC_BASE * max_ratio, > + 100 * BDI_RATIO_SCALE); > } Why use div64_u64 here? FPROP_FRAC_BASE is an unsigned long. max_ratio is an unsigned int, so the numerator is an unsigned long. BDI_RATIO_SCALE is 10,000, so the numerator is an unsigned int. There's no 64-bit arithmetic needed here.