From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236]) by e8.ny.us.ibm.com (8.13.1/8.13.1) with ESMTP id mA60OOqj026372 for ; Wed, 5 Nov 2008 19:24:24 -0500 Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id mA60S532105808 for ; Wed, 5 Nov 2008 19:28:05 -0500 Received: from d01av02.pok.ibm.com (loopback [127.0.0.1]) by d01av02.pok.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id mA60Rr6r001083 for ; Wed, 5 Nov 2008 19:27:54 -0500 Subject: Re: [linux-pm] [PATCH] hibernation should work ok with memory hotplug From: Dave Hansen In-Reply-To: <20081106091441.6517c072.kamezawa.hiroyu@jp.fujitsu.com> References: <20081029105956.GA16347@atrey.karlin.mff.cuni.cz> <1225817945.12673.602.camel@nimitz> <20081105093837.e073c373.kamezawa.hiroyu@jp.fujitsu.com> <200811051208.26628.rjw@sisk.pl> <20081106091441.6517c072.kamezawa.hiroyu@jp.fujitsu.com> Content-Type: text/plain Date: Wed, 05 Nov 2008 16:28:01 -0800 Message-Id: <1225931281.11514.27.camel@nimitz> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: KAMEZAWA Hiroyuki Cc: "Rafael J. Wysocki" , Yasunori Goto , Nigel Cunningham , Matt Tolentino , linux-pm@lists.osdl.org, Dave Hansen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, pavel@suse.cz, Mel Gorman , Andy Whitcroft , Andrew Morton List-ID: On Thu, 2008-11-06 at 09:14 +0900, KAMEZAWA Hiroyuki wrote: > Ok, please consider "when memory hotplug happens." > > In general, it happens when > 1. memory is inserted to slot. > 2. the firmware notifes the system to enable already inserted memory. > > To trigger "1", you have to open cover of server/pc. Do you open pc while the system > starts hibernation ? for usual people, no. You're right, this won't happen very often. We're trying to close a theoretical hole that hasn't ever been observed in practice. But, we don't exactly leave races in code just because we haven't observed them. I think this is a classic race. If we don't close it now, then someone doing some really weirdo hotplug is going to run into it at some point. Who knows what tomorrow's hardware/firmware will do? > To trigger "2", the user have special console to tell firmware "enable this memory". > Such firmware console or users have to know "the system works well." And, more important, > when the system is suspended, the firmware can't do hotplug because the kernel is sleeping. > So, such firmware console or operator have to know the system status. > > Am I missing some ? Current linux can know PCI/USB hotplug while the > system is suspended ? * echo 'disk' > /sys/power/state * count number of pages to write to disk * turn all interrupts off * copy pages to disk * power down I think the race we're trying to close is the one between when we count pages and when we turn interrupts off. I assume that there is a reason that we don't do the *entire* hibernation process with interrupts off, probably because it would "lock" the system up for too long, and can even possibly fail. -- Dave -- 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