Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757533Ab2JJXpH (ORCPT ); Wed, 10 Oct 2012 19:45:07 -0400 Received: from claw.goop.org ([74.207.240.146]:38172 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754784Ab2JJXpD (ORCPT ); Wed, 10 Oct 2012 19:45:03 -0400 X-Greylist: delayed 623 seconds by postgrey-1.27 at vger.kernel.org; Wed, 10 Oct 2012 19:45:03 EDT Message-ID: <5076060D.1030101@goop.org> Date: Wed, 10 Oct 2012 16:34:37 -0700 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120911 Thunderbird/15.0.1 MIME-Version: 1.0 To: Andrew Morton CC: KY Srinivasan , "gregkh@linuxfoundation.org" , "linux-kernel@vger.kernel.org" , "devel@linuxdriverproject.org" , "olaf@aepfle.de" , "apw@canonical.com" , "andi@firstfloor.org" Subject: Re: [PATCH 2/2] Drivers: hv: Add Hyper-V balloon driver References: <1349654347-18337-1-git-send-email-kys@microsoft.com> <1349654386-18378-1-git-send-email-kys@microsoft.com> <1349654386-18378-2-git-send-email-kys@microsoft.com> <20121009124449.f54bf8cb.akpm@linux-foundation.org> <426367E2313C2449837CD2DE46E7EAF930A33CC4@SN2PRD0310MB382.namprd03.prod.outlook.com> <20121009181458.e59e7094.akpm@linux-foundation.org> In-Reply-To: <20121009181458.e59e7094.akpm@linux-foundation.org> X-Enigmail-Version: 1.4.4 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1871 Lines: 39 On 10/09/2012 06:14 PM, Andrew Morton wrote: > On Wed, 10 Oct 2012 00:09:12 +0000 KY Srinivasan wrote: > >>>> + if (!pg) { >>>> + *alloc_error = true; >>>> + return i * alloc_unit; >>>> + } >>>> + >>>> + totalram_pages -= alloc_unit; >>> Well, I'd consider totalram_pages to be an mm-private thing which drivers >>> shouldn't muck with. Why is this done? >> By modifying the totalram_pages, the information presented in /proc/meminfo >> correctly reflects what is currently assigned to the guest (MemTotal). > eh? /proc/meminfo:MemTotal tells you the total memory in the machine. > The only thing which should change it after boot is memory hotplug. [...] > Why on earth do balloon drivers do this? If the amount of memory which > is consumed by balloons is interesting then it should be exported via a > standalone metric, not by mucking with totalram_pages. Balloon drivers are trying to fake a form of page-by-page memory hotplug. When they allocate memory from the kernel, they're actually giving the pages back to the hypervisor to redistribute to other guests. They reduce totalram_pages to try and reflect that the memory is no longer the kernel (in Xen, at least, the pfns will no longer have any physical page underlying them). I agree this is pretty ugly; it would be nice to have some better interface to indicate what's going on. At one point I tried to use the memory hotplug interfaces for larger-scale dynamic transfers of memory between a domain and the host, but when I last looked at it, it was too coarse grained and heavyweight to replace the balloon mechanism. J -- 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/