Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751629Ab2KFJFr (ORCPT ); Tue, 6 Nov 2012 04:05:47 -0500 Received: from mail-ea0-f174.google.com ([209.85.215.174]:42979 "EHLO mail-ea0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751119Ab2KFJFm (ORCPT ); Tue, 6 Nov 2012 04:05:42 -0500 Date: Tue, 6 Nov 2012 10:05:39 +0100 From: Michal Hocko To: KY Srinivasan Cc: Andrew Morton , Greg KH , "olaf@aepfle.de" , "linux-kernel@vger.kernel.org" , "andi@firstfloor.org" , "apw@canonical.com" , "devel@linuxdriverproject.org" , "linux-mm@kvack.org" , Hiroyuki Kamezawa , Johannes Weiner , Ying Han Subject: Re: [PATCH 1/2] mm: Export vm_committed_as Message-ID: <20121106090539.GB21167@dhcp22.suse.cz> References: <1349654347-18337-1-git-send-email-kys@microsoft.com> <1349654386-18378-1-git-send-email-kys@microsoft.com> <20121008004358.GA12342@kroah.com> <426367E2313C2449837CD2DE46E7EAF930A1FB31@SN2PRD0310MB382.namprd03.prod.outlook.com> <20121008133539.GA15490@kroah.com> <20121009124755.ce1087b4.akpm@linux-foundation.org> <426367E2313C2449837CD2DE46E7EAF930DF7FBB@SN2PRD0310MB382.namprd03.prod.outlook.com> <20121105134456.f655b85a.akpm@linux-foundation.org> <426367E2313C2449837CD2DE46E7EAF930DFA7B8@SN2PRD0310MB382.namprd03.prod.outlook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <426367E2313C2449837CD2DE46E7EAF930DFA7B8@SN2PRD0310MB382.namprd03.prod.outlook.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3116 Lines: 74 On Mon 05-11-12 22:12:25, KY Srinivasan wrote: > > > > -----Original Message----- > > From: Andrew Morton [mailto:akpm@linux-foundation.org] > > Sent: Monday, November 05, 2012 4:45 PM > > To: KY Srinivasan > > Cc: Greg KH; olaf@aepfle.de; linux-kernel@vger.kernel.org; andi@firstfloor.org; > > apw@canonical.com; devel@linuxdriverproject.org; linux-mm@kvack.org; > > Hiroyuki Kamezawa; Michal Hocko; Johannes Weiner; Ying Han > > Subject: Re: [PATCH 1/2] mm: Export vm_committed_as > > > > On Sat, 3 Nov 2012 14:09:38 +0000 > > KY Srinivasan wrote: > > > > > > > > > > > > > > > > > > Ok, but you're going to have to get the -mm developers to agree that > > > > > this is ok before I can accept it. > > > > > > > > Well I guess it won't kill us. > > > > > > Andrew, > > > > > > I presumed this was an Ack from you with regards to exporting the > > > symbol. Looks like Greg is waiting to hear from you before he can check > > > these patches in. Could you provide an explicit Ack. > > > > > > > Well, I do have some qualms about exporting vm_committed_as to modules. > > > > vm_committed_as is a global thing and only really makes sense in a > > non-containerised system. If the application is running within a > > memory cgroup then vm_enough_memory() and the global overcommit policy > > are at best irrelevant and misleading. > > > > If use of vm_committed_as is indeed a bad thing, then exporting it to > > modules might increase the amount of badness in the kernel. > > > > > > I don't think these qualms are serious enough to stand in the way of > > this patch, but I'd be interested in hearing the memcg developers' > > thoughts on the matter? > > > > > > Perhaps you could provide a detailed description of why your module > > actually needs this? Precisely what information is it looking for > > and why? If we know that then perhaps a more comfortable alternative > > can be found. > > The Hyper-V host has a policy engine for managing available physical > memory across competing virtual machines. This policy decision > is based on a number of parameters including the memory pressure > reported by the guest. Currently, the pressure calculation is based > on the memory commitment made by the guest. From what I can tell, the > ratio of currently allocated physical memory to the current memory > commitment made by the guest (vm_committed_as) is used as one of the > parameters in making the memory balancing decision on the host. This > is what Windows guests report to the host. So, I need some measure of > memory commitments made by the Linux guest. This is the reason I want > export vm_committed_as. So IIUC it will be guest who reports the value and the guest runs in the ring-0 so it is not in any user process context, right? If this is correct then memcg doesn't play any role here. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/