From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754181AbdBHPVg (ORCPT ); Wed, 8 Feb 2017 10:21:36 -0500 Received: from resqmta-ch2-07v.sys.comcast.net ([69.252.207.39]:59998 "EHLO resqmta-ch2-07v.sys.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752061AbdBHPVd (ORCPT ); Wed, 8 Feb 2017 10:21:33 -0500 Date: Wed, 8 Feb 2017 09:11:06 -0600 (CST) From: Christoph Lameter X-X-Sender: cl@east.gentwo.org To: Michal Hocko cc: Thomas Gleixner , Mel Gorman , Vlastimil Babka , Dmitry Vyukov , Tejun Heo , "linux-mm@kvack.org" , LKML , Ingo Molnar , Peter Zijlstra , syzkaller , Andrew Morton Subject: Re: mm: deadlock between get_online_cpus/pcpu_alloc In-Reply-To: <20170208073527.GA5686@dhcp22.suse.cz> Message-ID: References: <20170207113435.6xthczxt2cx23r4t@techsingularity.net> <20170207114327.GI5065@dhcp22.suse.cz> <20170207123708.GO5065@dhcp22.suse.cz> <20170207135846.usfrn7e4znjhmogn@techsingularity.net> <20170207141911.GR5065@dhcp22.suse.cz> <20170207153459.GV5065@dhcp22.suse.cz> <20170207162224.elnrlgibjegswsgn@techsingularity.net> <20170207164130.GY5065@dhcp22.suse.cz> <20170208073527.GA5686@dhcp22.suse.cz> Content-Type: text/plain; charset=US-ASCII X-CMAE-Envelope: MS4wfBxhLv6SOmPGQpP4SSEOftKjZ4d2+QdqmohoFytQdR+qJ1r8E0lb/hMiC4OvvJNna6VXox+qKr8l+C+HyYY9+171nBpHuPqAyM+P0AYreIhOQm4GGntF el2nLXVmBQNbJtP07PJcOlrEhg6pf1bKjim4nNjgH0myZoNi4NWALX0zbxLhvCBX5hmE9Xs96pOQ1zJD2EdMfSO3UU6Dtl8gQM9tW2RZTSzMhWa2FPYV4n12 MBpGSpktgTD+SArtEj3s4Wp4UyCKM1uDW+FxSAFqqwrY3KDy4nETaIuaQReFOzvfpv+NszkBp/yIYdwJUpbX7n55U/qBNG+NG9sWtRt/ohbvMzhiMkyE3QsS bLL7seqtNIyVAWmd9NQv6ruJru8Ron188NyNqB/MMMsTeht15WjKEv33bfD4gQvrInpALqQ24V46NmrWNwttgGRDDxv0FLfTA8wDGDzINO2jdqT22x/oLZBL h12puTu903ZuL8DSK+qnUvWM8npvF6mXb7UNVw== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 8 Feb 2017, Michal Hocko wrote: > > Huch? stop_machine() is horrible and heavy weight. Don't go there, there > > must be simpler solutions than that. > > Absolutely agreed. We are in the page allocator path so using the > stop_machine* is just ridiculous. And, in fact, there is a much simpler > solution [1] That is nonsense. stop_machine would be used when adding removing a processor. There would be no need to synchronize when looping over active cpus anymore. get_online_cpus() etc would be removed from the hot path since the cpu masks are guaranteed to be stable. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f198.google.com (mail-io0-f198.google.com [209.85.223.198]) by kanga.kvack.org (Postfix) with ESMTP id 1DCA66B0033 for ; Wed, 8 Feb 2017 10:11:09 -0500 (EST) Received: by mail-io0-f198.google.com with SMTP id j13so147392807iod.6 for ; Wed, 08 Feb 2017 07:11:09 -0800 (PST) Received: from resqmta-ch2-04v.sys.comcast.net (resqmta-ch2-04v.sys.comcast.net. [2001:558:fe21:29:69:252:207:36]) by mx.google.com with ESMTPS id b101si14935810ioj.150.2017.02.08.07.11.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 08 Feb 2017 07:11:08 -0800 (PST) Date: Wed, 8 Feb 2017 09:11:06 -0600 (CST) From: Christoph Lameter Subject: Re: mm: deadlock between get_online_cpus/pcpu_alloc In-Reply-To: <20170208073527.GA5686@dhcp22.suse.cz> Message-ID: References: <20170207113435.6xthczxt2cx23r4t@techsingularity.net> <20170207114327.GI5065@dhcp22.suse.cz> <20170207123708.GO5065@dhcp22.suse.cz> <20170207135846.usfrn7e4znjhmogn@techsingularity.net> <20170207141911.GR5065@dhcp22.suse.cz> <20170207153459.GV5065@dhcp22.suse.cz> <20170207162224.elnrlgibjegswsgn@techsingularity.net> <20170207164130.GY5065@dhcp22.suse.cz> <20170208073527.GA5686@dhcp22.suse.cz> Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Thomas Gleixner , Mel Gorman , Vlastimil Babka , Dmitry Vyukov , Tejun Heo , "linux-mm@kvack.org" , LKML , Ingo Molnar , Peter Zijlstra , syzkaller , Andrew Morton On Wed, 8 Feb 2017, Michal Hocko wrote: > > Huch? stop_machine() is horrible and heavy weight. Don't go there, there > > must be simpler solutions than that. > > Absolutely agreed. We are in the page allocator path so using the > stop_machine* is just ridiculous. And, in fact, there is a much simpler > solution [1] That is nonsense. stop_machine would be used when adding removing a processor. There would be no need to synchronize when looping over active cpus anymore. get_online_cpus() etc would be removed from the hot path since the cpu masks are guaranteed to be stable. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org