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bh=EPo3LVEpzVOEfXYBnBity1ZSDmfmPTYiTBNlP6gCwc4=; b=WZiGoyAIdVvdASF2zSWLpzwpOggPoPLoK9nGauUcFsTB5k8LD44Jd5OXf0WrxZr7G775Cb A87YhpH05Rr0g33n7TFKaLkMGQ7leN9TQtv5Tf6lEY26b3Vn8pwlctXSHlYyL4HajjBVsn iym8L2NC83EFOOMIWVTjaafJg/XJ8QT+TqCFgPinGwDh1LnVP9VBdDNIjTfGNM4L9e70zk A41/BzJKLgNryqpXLTs2fAAzP/gizkNlUgJ/ckLzY5sQfekZXrAkM8dc/Y5iCv7sdJrPjT KqliWNMUpFCFqhEVZjaM96oOGTL07B9GvgziVDBRFa1mDdP2g6RVDldM1hp+QA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1674239644; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=EPo3LVEpzVOEfXYBnBity1ZSDmfmPTYiTBNlP6gCwc4=; b=yUoCrzUdebt1eIGt/qxmKRm0Vs0plsYl5XUmgDSZ76wbWdMBLz4kD5Dw3+pa0gZ7C7uAIu 856zN+thPlWz22Aw== From: Sebastian Andrzej Siewior To: Hillf Danton 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 Message-ID: References: <20230117083817.togfwc5cy4g67e5r@techsingularity.net> <20230117165021.t5m7c2d6frbbfzig@techsingularity.net> <20230119011538.3247-1-hdanton@sina.com> <20230119135903.3524-1-hdanton@sina.com> <20230120093711.3862-1-hdanton@sina.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230120093711.3862-1-hdanton@sina.com> X-Rspamd-Queue-Id: 118B11C000D X-Stat-Signature: hkkddh1rwa8sc8myy58zpm95nfuhhyft X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1674239646-919876 X-HE-Meta: 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 Eh676Z2i awRjIZhsZ0u0xNOlECs39yLQ08cYnUnNcyA5MgEucdi0g0NBbGXBhAG5WsreXvvMSn8tOJ8pEntCN9wM= 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: On 2023-01-20 17:37:11 [+0800], Hillf Danton wrote: > > 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? No. > If not, why keep starving waiters after they pay the 40ms price? That kind of starvation will also happen if you have only spinlock_t locks and you say 3 RT tasks that acquire the lock back to back. And a few SCHED_OTHER tasks. Those 3 will be always be in front of the queue (as they skip the line) and the following SCHED_OTHER tasks will starve and never get the lock. So it is basically the same scenario. Sebastian