From nobody Mon Feb 9 06:00:11 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1517932478241899.8638390010824; Tue, 6 Feb 2018 07:54:38 -0800 (PST) Received: from localhost ([::1]:59613 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ej5Zt-0005nS-Bc for importer@patchew.org; Tue, 06 Feb 2018 10:54:37 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43411) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ej5WA-0002nu-2L for qemu-devel@nongnu.org; Tue, 06 Feb 2018 10:50:52 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ej5W0-00047W-Hy for qemu-devel@nongnu.org; Tue, 06 Feb 2018 10:50:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56244) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ej5Vz-00046i-Vl for qemu-devel@nongnu.org; Tue, 06 Feb 2018 10:50:36 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2D72665D11; Tue, 6 Feb 2018 15:50:35 +0000 (UTC) Received: from dgilbert-t530.redhat.com (ovpn-117-30.ams2.redhat.com [10.36.117.30]) by smtp.corp.redhat.com (Postfix) with ESMTP id 45A105D6A8; Tue, 6 Feb 2018 15:50:25 +0000 (UTC) From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, quintela@redhat.com Date: Tue, 6 Feb 2018 15:49:25 +0000 Message-Id: <20180206154936.13565-4-dgilbert@redhat.com> In-Reply-To: <20180206154936.13565-1-dgilbert@redhat.com> References: <20180206154936.13565-1-dgilbert@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 06 Feb 2018 15:50:35 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PULL 03/14] migration/savevm.c: set MAX_VM_CMD_PACKAGED_SIZE to 1ul << 32 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: lvivier@redhat.com, groug@kaod.org, peterx@redhat.com, ross.lagerwall@citrix.com, wei.w.wang@intel.com, danielhb@linux.vnet.ibm.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" From: Daniel Henrique Barboza MAX_VM_CMD_PACKAGED_SIZE is a constant used in qemu_savevm_send_packaged and loadvm_handle_cmd_packaged to determine whether a package is too big to be sent or received. qemu_savevm_send_packaged is called inside postcopy_start (migration/migration.c) to send the MigrationState in a single blob to the destination, using the MIG_CMD_PACKAGED subcommand, which will read it up using loadvm_handle_cmd_packaged. If the blob is larger than MAX_VM_CMD_PACKAGED_SIZE, an error is thrown and the postcopy migration is aborted. Both MAX_VM_CMD_PACKAGED_SIZE and MIG_CMD_PACKAGED were introduced by commit 11cf1d984b ("MIG_CMD_PACKAGED: Send a packaged chunk ..."). The constant has its original value of 1ul << 24 (16MB). The current MAX_VM_CMD_PACKAGED_SIZE value is not enough to support postcopy migration of bigger pseries guests. The blob size for a postcopy migration = of a pseries guest with the following setup: qemu-system-ppc64 --nographic -vga none -machine pseries,accel=3Dkvm -m 64G= \ -smp 1,maxcpus=3D32 -device virtio-blk-pci,drive=3Drootdisk \ -drive file=3Df27.qcow2,if=3Dnone,cache=3Dnone,format=3Dqcow2,id=3Drootdisk= \ -netdev user,id=3Du1 -net nic,netdev=3Du1 Goes around 12MB. Bumping the RAM to 128G makes the blob sizes goes to 20MB. With 256G the blob goes to 37MB - more than twice the current maximum size. At this moment the pseries machine can handle guests with up to 1TB of RAM, making this postcopy blob goes to 128MB of size approximately. Following the discussions made in [1], there is a need to understand what devices are aggressively consuming the blob in that manner and see if that can be mitigated. Until then, we can set MAX_VM_CMD_PACKAGED_SIZE to the maximum value allowed. Since the size is a 32 bit int variable, we can set it as 1ul << 32, giving a maximum blob size of 4G that is enough to support postcopy migration of 32TB RAM guests given the above constraints. [1] https://lists.nongnu.org/archive/html/qemu-devel/2018-01/msg06313.html Signed-off-by: Daniel Henrique Barboza Reported-by: Balamuruhan S Reviewed-by: Juan Quintela Signed-off-by: Juan Quintela Signed-off-by: Dr. David Alan Gilbert --- migration/savevm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/migration/savevm.c b/migration/savevm.c index b7908f62be..b8e9c532af 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -81,7 +81,7 @@ enum qemu_vm_cmd { MIG_CMD_MAX }; =20 -#define MAX_VM_CMD_PACKAGED_SIZE (1ul << 24) +#define MAX_VM_CMD_PACKAGED_SIZE UINT32_MAX static struct mig_cmd_args { ssize_t len; /* -1 =3D variable */ const char *name; --=20 2.14.3