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imf02.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf02.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.18 as permitted sender) smtp.mailfrom=hdanton@sina.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1674207450; a=rsa-sha256; cv=none; b=iJWSD+pnMMQ/jMK0X6bs6aPgUrsGpY4nMj7wFq+cm186FyjrS1ozKmO12iIcto0CZU/xfH o7ePzfg5KdIN4iAN+cDQYqg9NErRIExWLZqEp8Qc8B/5DAm7XvRoJCuFgYAOP8HidG2+tA +ztNxfrw0ii2XzzM322fxY91rb3TG74= Received: from unknown (HELO localhost.localdomain)([114.249.61.130]) by sina.com (172.16.97.35) with ESMTP id 63CA5FFC00017F01; Fri, 20 Jan 2023 17:33:50 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 57800715073640 From: Hillf Danton To: Sebastian Andrzej Siewior Cc: Mel Gorman , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Davidlohr Bueso , linux-mm@kvack.org, LKML Subject: Re: [PATCH v2] locking/rwbase: Prevent indefinite writer starvation Date: Fri, 20 Jan 2023 17:37:11 +0800 Message-Id: <20230120093711.3862-1-hdanton@sina.com> In-Reply-To: References: <20230117083817.togfwc5cy4g67e5r@techsingularity.net> <20230117165021.t5m7c2d6frbbfzig@techsingularity.net> <20230119011538.3247-1-hdanton@sina.com> <20230119135903.3524-1-hdanton@sina.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 4A4BF8001B X-Stat-Signature: 3zwaza5g5t9g3sxfmkxz7ehpodmndzgn X-HE-Tag: 1674207446-749882 X-HE-Meta: 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 uUzQ+qba laEYg0FvERxPFm3sY+3Y0+w9UtaqF4nUDeqBPBUBxgAqwQ2btwu60JLXlLaME87J4hgqzXcMnhucpc7cmMMWMRohC3qMXl70uYzQa X-Bogosity: Ham, tests=bogofilter, spamicity=0.014715, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 19 Jan 2023 17:36:22 +0100 Sebastian Andrzej Siewior > On 2023-01-19 21:59:03 [+0800], Hillf Danton wrote: > > On Thu, 19 Jan 2023 09:32:22 +0100 Sebastian Andrzej Siewior > > > > > > As far as Mel's efforts go, I am satisfied so far. > > > > If not because you can, could you specify why 4ms fails to cure starvation? > > It does not fail to cure the starvation. I haven't tested it myself but > base on Mel's description and the patch it very much looks like it cures > the writer starvation. > > If you don't like the 4ms, it could be 1ms or 40ms - it does not really > matter. The 4ms is aligned on the generic implementation which uses the > same value. Unless there is strong evidence to use something else I > don't see the need to diverse. I am fine with either 4ms or 40ms, or a second. Given the cure, does it still work when reader bias for RT tasks is allowed? If not, why keep starving waiters after they pay the 40ms price?