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Tue, 19 Dec 2023 02:03:50 +0000 (UTC) X-FDA: 81581921820.18.E2CD3A5 Received: from out30-100.freemail.mail.aliyun.com (out30-100.freemail.mail.aliyun.com [115.124.30.100]) by imf21.hostedemail.com (Postfix) with ESMTP id 4CA151C000B for ; Tue, 19 Dec 2023 02:03:46 +0000 (UTC) Authentication-Results: imf21.hostedemail.com; dkim=none; spf=pass (imf21.hostedemail.com: domain of jefflexu@linux.alibaba.com designates 115.124.30.100 as permitted sender) smtp.mailfrom=jefflexu@linux.alibaba.com; dmarc=pass (policy=none) header.from=alibaba.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1702951428; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+zDVJliNUoxO+aQxQNF6xBuweA+aX4fyJ3ZG2mJOeko=; b=VgFWauVSHhgi2mOrDjmvvYVLtIkG8oHY15CWG/JiQHDlLsGXr3UxvC5x5QIqGWDiLnqILf KO18QEABRWp0DZ50H/HPEY+Zmrkmhl1oKICn/HuSmrgS5v/LR04Qf1Qrrpf+Pj0iZ3aW7L oPyrqMDmr9DBd87+ntfCSFjkdLTzTIc= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1702951428; a=rsa-sha256; cv=none; b=5yKmcqdJX1wTPSXY8pvGPu6v7f95iRYUhcsnvL4qPorSYog0QmiY8fYCIy0hfxwZDUDXjF EtIyBZGtqBvVQAYjERD47JA9IUAtdpS+xNkKBLVoME6Zbq2HkABVyA4GJrOPyPyLQAqIX5 4oUGWEpdEWoTiQCdsmAk9B6pKpLuVRQ= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=none; spf=pass (imf21.hostedemail.com: domain of jefflexu@linux.alibaba.com designates 115.124.30.100 as permitted sender) smtp.mailfrom=jefflexu@linux.alibaba.com; dmarc=pass (policy=none) header.from=alibaba.com X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045192;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0VyogQL4_1702951421; Received: from 30.221.145.29(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0VyogQL4_1702951421) by smtp.aliyun-inc.com; Tue, 19 Dec 2023 10:03:42 +0800 Message-ID: <112dd87b-1072-4568-93d5-3b13ed818511@linux.alibaba.com> Date: Tue, 19 Dec 2023 10:03:40 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: fix arithmetic for bdi min_ratio and max_ratio Content-Language: en-US To: Andrew Morton Cc: shr@devkernel.io, linux-mm@kvack.org, linux-kernel@vger.kernel.org, joseph.qi@linux.alibaba.com References: <20231218031640.77983-1-jefflexu@linux.alibaba.com> <20231218102117.c91ab02353ff76b952f3ec9e@linux-foundation.org> From: Jingbo Xu In-Reply-To: <20231218102117.c91ab02353ff76b952f3ec9e@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 4CA151C000B X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: qq5wha7fhbbrsb7jzo38momsoryn8jz5 X-HE-Tag: 1702951426-916440 X-HE-Meta: U2FsdGVkX1+LfUOSZZrZaRXpTyfZpCAlksAf21hGQ/Z/17rvHPChusyOLwWEWApG2KpAsF6kCxO9/EoNhg0lxL9GzAFcov6VH50GMvDWfh5TtWaivk325v3H4NZM7yhGn/eEtQSOIXXj1D8ccvwiwicnYq5M2QhEMN8dN/b7RvM2biIFwEahtUs/PTWsrR82LXCH7y3072m8tHtvxG1w8ljUuGjOIMCxWlaXX0KULAGbo+phzPlisGx7yD58GASotmgvV9DzqQTlpWSLF0VhHCDFVYWZvFXff1VnPs5yOHfIQwJSOBO4I4HgjBgGommIwu0BX3WDnFu6ZKIXtL3eZsBhxc+0df3Yhge90I9Nb3EEl1n0G0geFcfYK4meoRnCoG/RxUztwAzN9SL6gYPyXO0zn+mqONkEZZvVWWTB0d6YQF+Gv7sYfzuvp+zyKFn/2egRfMqRe+WhPt5rzo65fu5YXq+lCOwwFE1Mm1LUTPpMfa9LKy1FX0oknSCO7q8u00UDteM9EY37G7Xwtez83D4GqNLX3rCsZHD+/aUtd8gjKPrv0TjXj02xMmNFtZiqbO/L+DRB2uPCFbJfcO4zkHUO9IqyKcLXbN6beX8zUgQuv9cEAR1uI7qI/vYsuI8lxEVTvMMt+mGdiMHt/rhCplmxhUY39Zm+gMKBzsVpLhnSXROhmf7M3xkxIpTHYOvIK8ciVk1PefTtDF8X6TbSNEgdVOcOI1sNSg1CoYtbWjle1B4sMrQon5uMP5S48W9GPH949DH7wsjlkr4lFOoSBcm2Lw5/WLtS20KrG4sJLwtyWZfCd3hqqp08aDaxZX+HqBop+UfkZga5FZLchRu9x7rnACdkGnWNLBbj/OTlj1S2mwCfxorxumcTAbOgDDwPUmiQdp/hs3Q0/JIWatr4mwU2KEMI/9YluoIkz55IVwWjI004AYNj1DKqIzgMzvUASqTrZyL13kJ6CkzApZU ZxJxHo0t BJS/lMxb0On77RBW4hvjlnTmR2IeP2+8QCmc9xCtZ23NFD6MNVZb+YsH89YZNG4drYzT+ZH8yhB02M9TMTo74Cvmbtk8EVj3pZfHgVmoPqym2oYVLRgZ6/OPE3DBlUOxSwUbxyFeUnM/8V2mbr+3VeREZbdE7nIXfwT3WIgCBghwInqkONOQT58FLAOOSUtsxfSFW7rUI/vVMTC/7JqxWs8jDvsm9eM9MRvXH4F+7KpPe9m1MAVlhMUoJnQ== 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 12/19/23 2:21 AM, Andrew Morton wrote: > On Mon, 18 Dec 2023 11:16:40 +0800 Jingbo Xu wrote: > >> bdi->[min|max]_ratio are both part per million. Fix the wrong >> arithmetic when setting bdi's min_ratio and max_ratio. >> >> Fixes: efc3e6ad53ea ("mm: split off __bdi_set_max_ratio() function") >> Fixes: 8021fb3232f2 ("mm: split off __bdi_set_min_ratio() function") > > As we have two Fixes:, it would be better to have two patches please. Sounds reasonable. Thanks. > >> --- a/mm/page-writeback.c >> +++ b/mm/page-writeback.c >> @@ -692,7 +692,6 @@ static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ra >> >> if (min_ratio > 100 * BDI_RATIO_SCALE) >> return -EINVAL; >> - min_ratio *= BDI_RATIO_SCALE; This indeed has visible runtime effect as follows: # cat /sys/class/bdi/253\:0/min_ratio 0 # cat /sys/class/bdi/253\:0/max_ratio 100 # echo 1 > /sys/class/bdi/253\:0/min_ratio -bash: echo: write error: Invalid argument Setting min_ratio will fail with -EINVAL, as the above code tries to set min_ratio with (min_ratio * BDI_RATIO_SCALE)%, i.e. 10000% in the above example. >> >> spin_lock_bh(&bdi_lock); >> if (min_ratio > bdi->max_ratio) { >> @@ -729,7 +728,8 @@ static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ra >> ret = -EINVAL; >> } 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, >> + 100UL * BDI_RATIO_SCALE); >> } >> spin_unlock_bh(&bdi_lock); This one has no visible runtime effect, but I believe this would affect the incrementing of writeout completion count when max_ratio is not 100%. -- Thanks, Jingbo