From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45880) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ze0uL-0001rK-3D for qemu-devel@nongnu.org; Mon, 21 Sep 2015 09:13:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Ze0uH-0001LY-3k for qemu-devel@nongnu.org; Mon, 21 Sep 2015 09:13:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:8702) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ze0uG-0001L7-Tr for qemu-devel@nongnu.org; Mon, 21 Sep 2015 09:13:21 -0400 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (Postfix) with ESMTPS id 7955DC0B2B49 for ; Mon, 21 Sep 2015 13:13:19 +0000 (UTC) References: <1442836223-282767-1-git-send-email-imammedo@redhat.com> <55FFF67F.5070701@redhat.com> <20150921150524.6d58bbbd@nial.brq.redhat.com> From: Paolo Bonzini Message-ID: <5600026D.4090407@redhat.com> Date: Mon, 21 Sep 2015 15:13:17 +0200 MIME-Version: 1.0 In-Reply-To: <20150921150524.6d58bbbd@nial.brq.redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] pc: memhotplug: rise minimum DIMM addr/size alignment to 128Mb List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Igor Mammedov Cc: mst@redhat.com, qemu-devel@nongnu.org, ehabkost@redhat.com On 21/09/2015 15:05, Igor Mammedov wrote: >> > To some extend, enforcing natural alignment would be okay as a >> > workaround for the virtio bug as well. It would also make it easier to >> > ensure that hotplugged hugetlbfs-backed memory can use hugepages in the >> > guest. Does it make sense to you? > in current machine types we already enforce backend-s address/size alignment, > which is file's page size for hugetlbfs-backed memory and 2Mb for RAM backend. Right, but it's not enough if the guest's physical address is not aligned to 2Mb/1Gb too. This is why we changed i440FX and q35 to have only 3 and 2 gigabytes of low memory (down from 3.5 and 2 IIRC). > So I guess we could try to apply workaround to virtio on guest side, > aligning and limiting max buffer size to 2Mb, it should work for 'old' > machine types as well. That would make sense and it would be complementary to natural alignment of DIMMs in the host. This would give: host guest old old fails old new works (virtio workaround) new old works (natural alignment) new new works (choose your favorite workaround) Paolo