Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751930Ab2KFOqs (ORCPT ); Tue, 6 Nov 2012 09:46:48 -0500 Received: from mail-ee0-f46.google.com ([74.125.83.46]:65302 "EHLO mail-ee0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750905Ab2KFOqr (ORCPT ); Tue, 6 Nov 2012 09:46:47 -0500 Date: Tue, 6 Nov 2012 15:46:44 +0100 From: Michal Hocko To: David Rientjes Cc: KY Srinivasan , 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: <20121106144644.GA29017@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: 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: 1634 Lines: 35 On Mon 05-11-12 14:33:12, David Rientjes wrote: > On Mon, 5 Nov 2012, KY Srinivasan wrote: > > > 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. > > > > I don't think you should export the symbol itself to modules but rather a > helper function that returns s64 that just wraps > percpu_counter_read_positive() which your driver could use instead. Agreed, we should rather make sure that nobody can manipulate the value from modules. > (And why percpu_counter_read_positive() returns a signed type is a > mystery.) Strange indeed. The last commit changed it from long to s64 to suport values bigger than 2^31 but even the original long doesn't make much sense to me. -- 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/