From nobody Mon Feb 9 06:00:19 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.zoho.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; Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1488287662797357.79272283164335; Tue, 28 Feb 2017 05:14:22 -0800 (PST) Received: from localhost ([::1]:60874 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cihbg-00051g-MK for importer@patchew.org; Tue, 28 Feb 2017 08:14:20 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40307) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cih6I-0000LC-4c for qemu-devel@nongnu.org; Tue, 28 Feb 2017 07:41:55 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cih6H-0000bp-DF for qemu-devel@nongnu.org; Tue, 28 Feb 2017 07:41:54 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57906) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cih6H-0000bY-79 for qemu-devel@nongnu.org; Tue, 28 Feb 2017 07:41:53 -0500 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4F8D74E4CB; Tue, 28 Feb 2017 12:41:53 +0000 (UTC) Received: from dgilbert-t530.redhat.com (ovpn-117-149.ams2.redhat.com [10.36.117.149]) by int-mx10.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id v1SCewtQ019858; Tue, 28 Feb 2017 07:41:51 -0500 From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org Date: Tue, 28 Feb 2017 12:40:55 +0000 Message-Id: <20170228124056.5074-27-dgilbert@redhat.com> In-Reply-To: <20170228124056.5074-1-dgilbert@redhat.com> References: <20170228124056.5074-1-dgilbert@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 28 Feb 2017 12:41:53 +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 26/27] postcopy: Add doc about hugepages and postcopy 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, pasic@linux.vnet.ibm.com, vsementsov@virtuozzo.com, quintela@redhat.com, ashijeetacharya@gmail.com, marcandre.lureau@redhat.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: "Dr. David Alan Gilbert" Signed-off-by: Dr. David Alan Gilbert Reviewed-by: Juan Quintela Reviewed-by: Laurent Vivier Message-Id: <20170224182844.32452-16-dgilbert@redhat.com> Signed-off-by: Dr. David Alan Gilbert --- docs/migration.txt | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/docs/migration.txt b/docs/migration.txt index c8b0304..1b940a8 100644 --- a/docs/migration.txt +++ b/docs/migration.txt @@ -540,3 +540,16 @@ request for a page that has already been sent is ignor= ed. Duplicate requests such as this can happen as a page is sent at about the same time the destination accesses it. =20 +=3D=3D=3D Postcopy with hugepages =3D=3D=3D + +Postcopy now works with hugetlbfs backed memory: + a) The linux kernel on the destination must support userfault on hugepag= es. + b) The huge-page configuration on the source and destination VMs must be + identical; i.e. RAMBlocks on both sides must use the same page size. + c) Note that -mem-path /dev/hugepages will fall back to allocating norm= al + RAM if it doesn't have enough hugepages, triggering (b) to fail. + Using -mem-prealloc enforces the allocation using hugepages. + d) Care should be taken with the size of hugepage used; postcopy with 2MB + hugepages works well, however 1GB hugepages are likely to be problema= tic + since it takes ~1 second to transfer a 1GB hugepage across a 10Gbps l= ink, + and until the full page is transferred the destination thread is bloc= ked. --=20 2.9.3