From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id 387BD6B0069 for ; Mon, 21 Nov 2011 03:23:03 -0500 (EST) Received: from /spool/local by e23smtp08.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 21 Nov 2011 08:21:21 +1000 Received: from d23av02.au.ibm.com (d23av02.au.ibm.com [9.190.235.138]) by d23relay05.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id pAL8JRiV3252394 for ; Mon, 21 Nov 2011 19:19:27 +1100 Received: from d23av02.au.ibm.com (loopback [127.0.0.1]) by d23av02.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id pAL8MhQD010442 for ; Mon, 21 Nov 2011 19:22:44 +1100 Message-ID: <4ECA0A50.7030502@linux.vnet.ibm.com> Date: Mon, 21 Nov 2011 13:52:40 +0530 From: "Srivatsa S. Bhat" MIME-Version: 1.0 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> <4ECA03DF.4000402@linux.intel.com> In-Reply-To: <4ECA03DF.4000402@linux.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Chen Gong Cc: "Rafael J. Wysocki" , pavel@ucw.cz, lenb@kernel.org, ak@linux.intel.com, tj@kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-mm@kvack.org On 11/21/2011 01:25 PM, Chen Gong wrote: > [...] >> >> Actually, I think I have a better idea based on a key observation: >> We are trying to acquire pm_mutex here. And if we block due to this, >> we are *100% sure* that we are not going to run as long as hibernation >> sequence is running, since hibernation releases pm_mutex only at the >> very end, when everything is done. >> And this means, this task is going to be blocked for much more longer >> than what the freezer intends to achieve. Which means, freezing and >> thawing doesn't really make a difference to this task! >> >> So, let's just ask the freezer to skip freezing us!! And everything >> will be just fine! >> >> Something like: >> >> 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. >> > > This new design looks clean and better than old one. I just curious how do > you design your test environment? e.g. when hibernating is in progress, > try to online some memories and wait for hibernation fails or succeeds? > Hi Chen, Thanks a lot for taking a look! As I have indicated earlier in some of my mails, I am more concerned about the API lock_system_sleep() than memory hotplug, because it is this *API* that is buggy, not memory-hotplug. And going further, any other code planning to use this API will be problematic. So our focus here, is to fix this *API*. So, to test this API, I have written a kernel module that calls lock_system_sleep() in its init code. Then I load/unload that module wildly in a loop and simultaneously run hibernation tests using the 'pm_test' framework. It is to be also noted that, the issue here is only with the initial steps of hibernation, namely, related to freezer. Hence, pm_test framework fits pretty well to debug these freezer issues. (And in fact, I have found that this method is quite effective to test whether my patch fixes the issue or not.) Thanks, Srivatsa S. Bhat -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org