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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 3FCEFC00A8F for ; Tue, 24 Oct 2023 05:34:36 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qvA30-0001IX-2r; Tue, 24 Oct 2023 01:33:46 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qvA2x-0001Hv-Pg for qemu-devel@nongnu.org; Tue, 24 Oct 2023 01:33:43 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qvA2w-0001GP-4v for qemu-devel@nongnu.org; Tue, 24 Oct 2023 01:33:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1698125620; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=D2S/cPEjx0Mu1ahqSAWxy0Q5ppS1XGigbe0/WSd4mSk=; b=XeqIBtUHzv5xaeIcgLXsPah6/lkEgnXhElgVBGEtroTYLkPPZ2/EZO6YG7QrMSWT9jsazX ag+tChSFZuAgQlZuTRLlWtUTTmXwOK1BG7QfYHNihuj28ah2m94BpfrPqr02TUrjLWuViC 9NyBusBUdUoIFyRytkVT4vwjCB1RsXc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-54-QhDH6B5mOUa7RrMazww_gw-1; Tue, 24 Oct 2023 01:33:37 -0400 X-MC-Unique: QhDH6B5mOUa7RrMazww_gw-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id AAD10101A594; Tue, 24 Oct 2023 05:33:36 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.193.56]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 896BB492BFB; Tue, 24 Oct 2023 05:33:36 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 3845621E6A1F; Tue, 24 Oct 2023 07:33:34 +0200 (CEST) From: Markus Armbruster To: Fabiano Rosas Cc: qemu-devel@nongnu.org, berrange@redhat.com, Juan Quintela , Peter Xu , Leonardo Bras , Claudio Fontana , Eric Blake Subject: Re: [PATCH v2 14/29] migration/ram: Introduce 'fixed-ram' migration capability References: <20231023203608.26370-1-farosas@suse.de> <20231023203608.26370-15-farosas@suse.de> Date: Tue, 24 Oct 2023 07:33:34 +0200 In-Reply-To: <20231023203608.26370-15-farosas@suse.de> (Fabiano Rosas's message of "Mon, 23 Oct 2023 17:35:53 -0300") Message-ID: <87fs20vb2p.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.10 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Fabiano Rosas writes: > Add a new migration capability 'fixed-ram'. > > The core of the feature is to ensure that each ram page has a specific > offset in the resulting migration stream. The reason why we'd want > such behavior are two fold: > > - When doing a 'fixed-ram' migration the resulting file will have a > bounded size, since pages which are dirtied multiple times will > always go to a fixed location in the file, rather than constantly > being added to a sequential stream. This eliminates cases where a vm > with, say, 1G of ram can result in a migration file that's 10s of > GBs, provided that the workload constantly redirties memory. > > - It paves the way to implement DIRECT_IO-enabled save/restore of the > migration stream as the pages are ensured to be written at aligned > offsets. > > For now, enabling the capability has no effect. The next couple of > patches implement the core funcionality. > > Signed-off-by: Fabiano Rosas > --- > docs/devel/migration.rst | 14 ++++++++++++++ > migration/options.c | 37 +++++++++++++++++++++++++++++++++++++ > migration/options.h | 1 + > migration/savevm.c | 1 + > qapi/migration.json | 5 ++++- > 5 files changed, 57 insertions(+), 1 deletion(-) > > diff --git a/docs/devel/migration.rst b/docs/devel/migration.rst > index c3e1400c0c..6f898b5dbd 100644 > --- a/docs/devel/migration.rst > +++ b/docs/devel/migration.rst > @@ -566,6 +566,20 @@ Others (especially either older devices or system devices which for > some reason don't have a bus concept) make use of the ``instance id`` > for otherwise identically named devices. > > +Fixed-ram format > +---------------- > + > +When the ``fixed-ram`` capability is enabled, a slightly different > +stream format is used for the RAM section. Instead of having a > +sequential stream of pages that follow the RAMBlock headers, the dirty > +pages for a RAMBlock follow its header. This ensures that each RAM > +page has a fixed offset in the resulting migration stream. This requires the migration stream to be seekable, as documented in the QAPI schema below. I think it's worth documenting here, as well. > + > +The ``fixed-ram`` capaility can be enabled in both source and > +destination with: > + > + ``migrate_set_capability fixed-ram on`` Effect of enabling on the destination? What happens when we enable it only on one end? > + > Return path > ----------- > [...] > diff --git a/qapi/migration.json b/qapi/migration.json > index 74f12adc0e..1317dd32ab 100644 > --- a/qapi/migration.json > +++ b/qapi/migration.json > @@ -527,6 +527,9 @@ > # VM before migration for an optimal migration performance. > # Enabled by default. (since 8.1) > # > +# @fixed-ram: Migrate using fixed offsets for each RAM page. Requires Two spaces between sentences for consistency, please. > +# a seekable transport such as a file. (since 8.1) What is a migration transport? migration.json doesn't define the term. Which transports are seekable? Out of curiosity: what happens if the transport isn't seekable? > +# > # Features: > # > # @unstable: Members @x-colo and @x-ignore-shared are experimental. > @@ -543,7 +546,7 @@ > { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] }, > 'validate-uuid', 'background-snapshot', > 'zero-copy-send', 'postcopy-preempt', 'switchover-ack', > - 'dirty-limit', 'auto-pause'] } > + 'dirty-limit', 'auto-pause', 'fixed-ram'] } > > ## > # @MigrationCapabilityStatus: