From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755807Ab1KUREw (ORCPT ); Mon, 21 Nov 2011 12:04:52 -0500 Received: from e28smtp01.in.ibm.com ([122.248.162.1]:38127 "EHLO e28smtp01.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751623Ab1KUREu (ORCPT ); Mon, 21 Nov 2011 12:04:50 -0500 Message-ID: <4ECA84A8.5030005@linux.vnet.ibm.com> Date: Mon, 21 Nov 2011 22:34:40 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux i686; rv:7.0) Gecko/20110927 Thunderbird/7.0 MIME-Version: 1.0 To: Tejun Heo CC: "Rafael J. Wysocki" , pavel@ucw.cz, lenb@kernel.org, ak@linux.intel.com, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v3] PM/Memory-hotplug: Avoid task freezing failures References: <20111117083042.11419.19871.stgit@srivatsabhat.in.ibm.com> <201111192257.19763.rjw@sisk.pl> <4EC8984E.30005@linux.vnet.ibm.com> <201111201124.17528.rjw@sisk.pl> <4EC9D557.9090008@linux.vnet.ibm.com> <20111121164006.GB15314@google.com> In-Reply-To: <20111121164006.GB15314@google.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit x-cbid: 11112117-4790-0000-0000-00000013EA46 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/21/2011 10:10 PM, Tejun Heo wrote: > Hello, Srivatsa. > > On Mon, Nov 21, 2011 at 10:06:39AM +0530, Srivatsa S. Bhat wrote: >> void lock_system_sleep(void) >> { >> /* simplified freezer_do_not_count() */ >> current->flags |= PF_FREEZER_SKIP; >> >> mutex_lock(&pm_mutex); >> >> } >> >> void unlock_system_sleep(void) >> { >> mutex_unlock(&pm_mutex); >> >> /* simplified freezer_count() */ >> current->flags &= ~PF_FREEZER_SKIP; >> >> } >> >> We probably don't want the restriction that freezer_do_not_count() and >> freezer_count() work only for userspace tasks. So I have open coded >> the relevant parts of those functions here. >> >> I haven't tested this solution yet. Let me know if this solution looks >> good and I'll send it out as a patch after testing and analyzing some >> corner cases, if any. I tested this, and it works great! I'll send the patch in some time. > > Ooh ooh, I definitely like this one much better. Thanks :-) Even I like it far better than all those ugly hacks I proposed earlier ;-) > Oleg did something > similar w/ wait_event_freezekillable() too. On related notes, > > * I think it would be better to remove direct access to pm_mutex and > use [un]lock_system_sleep() universally. I don't think hinging it > on CONFIG_HIBERNATE_CALLBACKS buys us anything. > Which direct access to pm_mutex are you referring to? Other than suspend/hibernation call paths, I think mem-hotplug is the only subsystem trying to access pm_mutex. I haven't checked thoroughly though. But yes, using lock_system_sleep() for mutually excluding some code path from suspend/hibernation is good, and that is one reason why I wanted to fix this API ASAP. But as long as memory hotplug is the only direct user of pm_mutex, is it justified to remove the CONFIG_HIBERNATE_CALLBACKS restriction and make it generic? I don't know... Or, are you saying that we should use these APIs even in suspend/hibernate call paths? That's not such a bad idea either... [ On a totally different note, I was wondering:- if mem-hotplug wants to exclude itself from hibernation alone, CONFIG_HIBERNATE_CALLBACKS is not the right way to do it, because, it would still unintentionally exclude itself from suspend also! (if suspend and hibernation are both enabled). I don't think we should worry about this too much, because we don't get much benefit trying to make mem-hotplug co-exist with suspend.. In fact, I would say, its even better to let it be this way and exclude suspend as well, since running exotic stuff like memory hotplug during suspend or hibernation is best avoided ;-) ] > * In the longer term, we should be able to toggle PF_NOFREEZE instead > as SKIP doesn't mean anything different. We'll probably need a > better API tho. But for now SKIP should work fine. > Yep, I agree. Thanks, Srivatsa S. Bhat