From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-131.freemail.mail.aliyun.com (out30-131.freemail.mail.aliyun.com [115.124.30.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4E4101D528; Tue, 19 Dec 2023 14:12:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R191e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045176;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0Vyr8ugS_1702994833; Received: from 192.168.31.58(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0Vyr8ugS_1702994833) by smtp.aliyun-inc.com; Tue, 19 Dec 2023 22:07:14 +0800 Message-ID: Date: Tue, 19 Dec 2023 22:07:12 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] mm: fix arithmetic for max_prop_frac when setting max_ratio Content-Language: en-US To: Matthew Wilcox 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 References: <20231219024246.65654-1-jefflexu@linux.alibaba.com> <20231219024246.65654-3-jefflexu@linux.alibaba.com> <5460aaf1-44f6-475f-b980-cb9058cc1df4@linux.alibaba.com> From: Jingbo Xu In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 12/19/23 9:01 PM, Matthew Wilcox wrote: > On Tue, Dec 19, 2023 at 01:58:21PM +0800, Jingbo Xu wrote: >> On 12/19/23 12:06 PM, Matthew Wilcox wrote: >>> 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. >> >> Yes, div64_u64() is actually not needed here. So it seems >> >> bdi->max_prop_frac = FPROP_FRAC_BASE * max_ratio / 100 / BDI_RATIO_SCALE; >> >> is adequate? > > I'd rather spell that as: > > bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / > (100 * BDI_RATIO_SCALE); > > It's closer to how you'd write it out mathematically and so it reads > more easily. At least for me. Thanks, I would send v3 soon. -- Thanks, Jingbo