From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50464) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VkwK3-0003eg-A1 for qemu-devel@nongnu.org; Mon, 25 Nov 2013 08:35:37 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VkwJu-0008Jt-J0 for qemu-devel@nongnu.org; Mon, 25 Nov 2013 08:35:31 -0500 Received: from mx1.redhat.com ([209.132.183.28]:15812) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VkwJu-0008JM-9G for qemu-devel@nongnu.org; Mon, 25 Nov 2013 08:35:22 -0500 Date: Mon, 25 Nov 2013 14:34:58 +0100 From: Igor Mammedov Message-ID: <20131125143458.24148c4e@nial.usersys.redhat.com> In-Reply-To: <1385379545.25009.22.camel@nilsson.home.kraxel.org> References: <1385001528-12003-1-git-send-email-imammedo@redhat.com> <1385001528-12003-22-git-send-email-imammedo@redhat.com> <1385130236.3681.94.camel@nilsson.home.kraxel.org> <20131125120019.7b6d4140@nial.usersys.redhat.com> <1385379545.25009.22.camel@nilsson.home.kraxel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 21/27] pc: add memory hotplug 440fx machine List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gerd Hoffmann Cc: peter.maydell@linaro.org, aliguori@amazon.com, stefanb@linux.vnet.ibm.com, qemu-devel@nongnu.org, hutao@cn.fujitsu.com, mst@redhat.com, mjt@tls.msk.ru, mdroth@linux.vnet.ibm.com, armbru@redhat.com, vasilis.liaskovitis@profitbricks.com, quintela@redhat.com, stefanha@redhat.com, pbonzini@redhat.com, marcel.a@redhat.com, lcapitulino@redhat.com, chegu_vinod@hp.com, afaerber@suse.de On Mon, 25 Nov 2013 12:39:05 +0100 Gerd Hoffmann wrote: > > > Does it make sense to hotplug memory above 4g unconditionally to > > > simplify things? > > It does and it was so in v6 RFC, > > But it would rule out hotplug for 32-bit guests that doesn't support > > more then 4Gb. > > Indeed. > > > As use case 32-bit guest could start whit small initial memory > > and hotplug additional memory if needed up to point where 32-bit > > PCI hole starts. That would allow guests to launch with small amount > > but baloon up upto 2-3.5 Gb depending on machine type. > > I could drop 32-bit guest support and do only high mem hotplug if > > this case it not interesting to the comunity, any suggestions? > > 32bit limits start to hurt with 1GB already. Kernel address space is 1G > on 32bit, so the kernel can't map all RAM all the time any more. Which > in turn adds overhead for mapping/unmapping pages if the kernel must > access highmem pages. So it's better to run 64bit guests even with alot > less than 4G of memory. > > I'd tend to just not support 32bit guests, I think it simply isn't worth > the trouble. Fine with me, If there isn't abjection to it, I'll drop 32-bit guest support on the next respin. > cheers, > Gerd > >