From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751122AbdCQMio (ORCPT ); Fri, 17 Mar 2017 08:38:44 -0400 Received: from mga04.intel.com ([192.55.52.120]:44646 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751035AbdCQMim (ORCPT ); Fri, 17 Mar 2017 08:38:42 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.36,176,1486454400"; d="scan'208";a="1123988945" Date: Fri, 17 Mar 2017 20:33:15 +0800 From: Aaron Lu To: Michal Hocko Cc: Tim Chen , Peter Zijlstra , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Hansen , Tim Chen , Andrew Morton , Ying Huang Subject: Re: [PATCH v2 0/5] mm: support parallel free of memory Message-ID: <20170317123315.GA1929@aaronlu.sh.intel.com> References: <1489568404-7817-1-git-send-email-aaron.lu@intel.com> <20170315141813.GB32626@dhcp22.suse.cz> <20170315154406.GF2442@aaronlu.sh.intel.com> <20170315162843.GA27197@dhcp22.suse.cz> <1489613914.2733.96.camel@linux.intel.com> <20170316090732.GF30501@dhcp22.suse.cz> <1489689381.2733.114.camel@linux.intel.com> <20170317074707.GB26298@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170317074707.GB26298@dhcp22.suse.cz> User-Agent: Mutt/1.8.0 (2017-02-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 17, 2017 at 08:47:08AM +0100, Michal Hocko wrote: > On Thu 16-03-17 11:36:21, Tim Chen wrote: > [...] > > Perhaps we can only do this expedited exit only when there are idle cpus around. > > We can use the root sched domain's overload indicator for such a quick check. > > This is not so easy, I am afraid. Those CPUs might be idle for a good > reason (power saving etc.). You will never know by simply checking Is it that those CPUs are deliberately put into idle mode to save power? IIRC, idle injection driver could be used to do this and if so, the injected idle task is a realtime one so the spawned kworker will not be able to preempt(disturb) it. > one metric. This is why doing these optimistic parallelization > optimizations is far from trivial. This is not the first time somebody > wants to do this. People are trying to make THP migration faster > doing the similar thing. I guess we really need a help from the > scheduler to do this properly, though. I've been thinking about an API > (e.g. try_to_run_in_backgroun) which would evaluate all these nasty > details and either return with -EBUSY or kick the background thread to > accomplish the work if the system is reasonably idle. I am not really > sure whether such an API is viable though. Peter, what do you think? I would very much like to know what these nasty details are and what 'reasonably idle' actually means, I think they are useful to understand the problem and define the API. I totally agree that we shouldn't distrub the system by starting more workers/threads to do spin work or to make a process utilizing more CPU or other resources than allowed by its cgroup. Thanks. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id E03BA6B0038 for ; Fri, 17 Mar 2017 08:33:06 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id p189so47935691pfp.5 for ; Fri, 17 Mar 2017 05:33:06 -0700 (PDT) Received: from mga14.intel.com (mga14.intel.com. [192.55.52.115]) by mx.google.com with ESMTPS id v185si8537608pgv.305.2017.03.17.05.33.05 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 17 Mar 2017 05:33:05 -0700 (PDT) Date: Fri, 17 Mar 2017 20:33:15 +0800 From: Aaron Lu Subject: Re: [PATCH v2 0/5] mm: support parallel free of memory Message-ID: <20170317123315.GA1929@aaronlu.sh.intel.com> References: <1489568404-7817-1-git-send-email-aaron.lu@intel.com> <20170315141813.GB32626@dhcp22.suse.cz> <20170315154406.GF2442@aaronlu.sh.intel.com> <20170315162843.GA27197@dhcp22.suse.cz> <1489613914.2733.96.camel@linux.intel.com> <20170316090732.GF30501@dhcp22.suse.cz> <1489689381.2733.114.camel@linux.intel.com> <20170317074707.GB26298@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170317074707.GB26298@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Tim Chen , Peter Zijlstra , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Hansen , Tim Chen , Andrew Morton , Ying Huang On Fri, Mar 17, 2017 at 08:47:08AM +0100, Michal Hocko wrote: > On Thu 16-03-17 11:36:21, Tim Chen wrote: > [...] > > Perhaps we can only do this expedited exit only when there are idle cpus around. > > We can use the root sched domain's overload indicator for such a quick check. > > This is not so easy, I am afraid. Those CPUs might be idle for a good > reason (power saving etc.). You will never know by simply checking Is it that those CPUs are deliberately put into idle mode to save power? IIRC, idle injection driver could be used to do this and if so, the injected idle task is a realtime one so the spawned kworker will not be able to preempt(disturb) it. > one metric. This is why doing these optimistic parallelization > optimizations is far from trivial. This is not the first time somebody > wants to do this. People are trying to make THP migration faster > doing the similar thing. I guess we really need a help from the > scheduler to do this properly, though. I've been thinking about an API > (e.g. try_to_run_in_backgroun) which would evaluate all these nasty > details and either return with -EBUSY or kick the background thread to > accomplish the work if the system is reasonably idle. I am not really > sure whether such an API is viable though. Peter, what do you think? I would very much like to know what these nasty details are and what 'reasonably idle' actually means, I think they are useful to understand the problem and define the API. I totally agree that we shouldn't distrub the system by starting more workers/threads to do spin work or to make a process utilizing more CPU or other resources than allowed by its cgroup. Thanks. -- 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