Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758225Ab3CDRGa (ORCPT ); Mon, 4 Mar 2013 12:06:30 -0500 Received: from e31.co.us.ibm.com ([32.97.110.149]:56193 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757398Ab3CDRG3 (ORCPT ); Mon, 4 Mar 2013 12:06:29 -0500 Message-ID: <5134D476.3040302@linux.vnet.ibm.com> Date: Mon, 04 Mar 2013 09:05:58 -0800 From: Dave Hansen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: KY Srinivasan CC: Greg KH , "linux-kernel@vger.kernel.org" , "devel@linuxdriverproject.org" , "olaf@aepfle.de" , "apw@canonical.com" , "andi@firstfloor.org" , "akpm@linux-foundation.org" , "linux-mm@kvack.org" Subject: Re: [PATCH 1/1] mm: Export split_page(). References: <1362364075-14564-1-git-send-email-kys@microsoft.com> <20130304020747.GA8265@kroah.com> <3a362e994ab64efda79ae3c80342db95@SN2PR03MB061.namprd03.prod.outlook.com> <20130304022508.GA8638@kroah.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13030417-7282-0000-0000-000014E5CD4A Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1763 Lines: 36 On 03/03/2013 06:36 PM, KY Srinivasan wrote: >> I guess the most obvious question about exporting this symbol is, "Why >> doesn't any of the other hypervisor balloon drivers need this? What is >> so special about hyper-v?" > > The balloon protocol that Hyper-V has specified is designed around the ability to > move 2M pages. While the protocol can handle 4k allocations, it is going to be very chatty > with 4K allocations. What does "very chatty" mean? Do you think that there will be a noticeable performance difference ballooning 2M pages vs 4k? > Furthermore, the Memory Balancer on the host is also designed to work > best with memory moving around in 2M chunks. While I have not seen the code on the Windows > host that does this memory balancing, looking at how Windows guests behave in this environment, > (relative to Linux) I have to assume that the 2M allocations that Windows guests do are a big part of > the difference we see. You've been talking about differences. Could you elaborate on what the differences in behavior are that you are trying to rectify here? >> Or can those other drivers also need/use it as well, and they were just >> too chicken to be asking for the export? :) > > The 2M balloon allocations would make sense if the host is designed accordingly. How does the guest decide which size pages to allocate? It seems like a relatively bad idea to be inflating the balloon with 2M pages from the guest in the case where the guest is under memory pressure _and_ fragmented. -- 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/