From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4F7F5C432C1 for ; Wed, 25 Sep 2019 11:52:07 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1F79D21D7A for ; Wed, 25 Sep 2019 11:52:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1F79D21D7A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:48468 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iD5q1-0004Bm-Jz for qemu-devel@archiver.kernel.org; Wed, 25 Sep 2019 07:52:05 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49615) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iD5pF-0003i0-73 for qemu-devel@nongnu.org; Wed, 25 Sep 2019 07:51:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iD5pD-0005IU-8X for qemu-devel@nongnu.org; Wed, 25 Sep 2019 07:51:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34384) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iD5pD-0005Hq-2j; Wed, 25 Sep 2019 07:51:15 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 83B30305FC56; Wed, 25 Sep 2019 11:51:12 +0000 (UTC) Received: from localhost (unknown [10.43.2.182]) by smtp.corp.redhat.com (Postfix) with ESMTP id CA746196B2; Wed, 25 Sep 2019 11:51:06 +0000 (UTC) Date: Wed, 25 Sep 2019 13:51:05 +0200 From: Igor Mammedov To: Peter Xu Subject: Re: [PATCH v7 4/4] s390: do not call memory_region_allocate_system_memory() multiple times Message-ID: <20190925135105.6e5f249a@redhat.com> In-Reply-To: <20190925032700.GI28074@xz-x1> References: <20190924144751.24149-1-imammedo@redhat.com> <20190924144751.24149-5-imammedo@redhat.com> <20190925032700.GI28074@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Wed, 25 Sep 2019 11:51:12 +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 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: thuth@redhat.com, david@redhat.com, cohuck@redhat.com, qemu-devel@nongnu.org, borntraeger@de.ibm.com, qemu-s390x@nongnu.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 25 Sep 2019 11:27:00 +0800 Peter Xu wrote: > On Tue, Sep 24, 2019 at 10:47:51AM -0400, Igor Mammedov wrote: > > s390 was trying to solve limited KVM memslot size issue by abusing > > memory_region_allocate_system_memory(), which breaks API contract > > where the function might be called only once. > > > > Beside an invalid use of API, the approach also introduced migration > > issue, since RAM chunks for each KVM_SLOT_MAX_BYTES are transferred in > > migration stream as separate RAMBlocks. > > > > After discussion [1], it was agreed to break migration from older > > QEMU for guest with RAM >8Tb (as it was relatively new (since 2.12) > > and considered to be not actually used downstream). > > Migration should keep working for guests with less than 8TB and for > > more than 8TB with QEMU 4.2 and newer binary. > > In case user tries to migrate more than 8TB guest, between incompatible > > QEMU versions, migration should fail gracefully due to non-exiting > > RAMBlock ID or RAMBlock size mismatch. > > > > Taking in account above and that now KVM code is able to split too > > big MemorySection into several memslots, partially revert commit > > (bb223055b s390-ccw-virtio: allow for systems larger that 7.999TB) > > and use kvm_set_max_memslot_size() to set KVMSlot size to > > KVM_SLOT_MAX_BYTES. > > > > 1) [PATCH RFC v2 4/4] s390: do not call memory_region_allocate_system_memory() multiple times > > > > Signed-off-by: Igor Mammedov > > Acked-by: Peter Xu > > IMHO it would be good to at least mention bb223055b9 in the commit > message even if not with a "Fixed:" tag. May be amended during commit > if anyone prefers. /me confused, bb223055b9 is mentioned in commit message > Also, this only applies the split limitation to s390. Would that be a > good thing to some other archs as well? Don't we have the similar bitmap size issue in KVM for other archs? > > Thanks, >