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 8DF82C0032E for ; Wed, 25 Oct 2023 06:20:26 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qvXEf-0000cd-KZ; Wed, 25 Oct 2023 02:19:22 -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 1qvXEe-0000bq-7Y for qemu-devel@nongnu.org; Wed, 25 Oct 2023 02:19:20 -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 1qvXEY-0000lQ-I5 for qemu-devel@nongnu.org; Wed, 25 Oct 2023 02:19:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1698214752; 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=Qz9nibAudhAmTPodeSx0XLITFaKh7AO80kVAgHaWlMM=; b=P+mi1LOs0iam8E5qgh6VSz6RmjL7/EEQVE4jiRrJCqhfCi2tqC2fY4KzSNI7LwKBV8LFH+ jclaATB2GNm0YZ7RoKuwNUSwPMIx5FQUu8eopzjScRDvPP+om2V5wTAIvtry1jS8mMrIr0 uOQt6YqFNyWuXXF30Y5E/LaVIHAmNqI= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-426-3pTSsSTfO9uA7oDZ6XZScw-1; Wed, 25 Oct 2023 02:19:00 -0400 X-MC-Unique: 3pTSsSTfO9uA7oDZ6XZScw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (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 813C33C0FC85; Wed, 25 Oct 2023 06:19:00 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.193.56]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 443252026D4C; Wed, 25 Oct 2023 06:19:00 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id DE4FD21E6A1F; Wed, 25 Oct 2023 08:18:58 +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> <87fs20vb2p.fsf@pond.sub.org> <87zg07dg1u.fsf@suse.de> Date: Wed, 25 Oct 2023 08:18:58 +0200 In-Reply-To: <87zg07dg1u.fsf@suse.de> (Fabiano Rosas's message of "Tue, 24 Oct 2023 15:35:41 -0300") Message-ID: <87sf5zkywd.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 10.11.54.4 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: > Markus Armbruster writes: > >> 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. >> > > Ok. > >>> + >>> +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? >> > > qemu-system-x86_64: Capability fixed-ram is off, but received capability is on > qemu-system-x86_64: load of migration failed: Invalid argument > > So I guess that *can* be enabled up there should become a *must*. Makes sense. >>> + >>> 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. >> > > The medium that transports the migration. We are about to define some > terms at the QAPI series: > > [PATCH v15 00/14] migration: Modify 'migrate' and 'migrate-incoming' > QAPI commands for migration > https://lore.kernel.org/r/20231023182053.8711-1-farosas@suse.de Can't find it there offhand. No need to explain it further to me now, just make sure it's defined at this point in the series when you respin. >> Which transports are seekable? >> > > The ones that implement QIO_CHANNEL_FEATURE_SEEKABLE. Currently only > QIOChannelFile. Transport seekability needs to be documented clearly. >> Out of curiosity: what happens if the transport isn't seekable? > > We fail the migration. At migration_channels_and_uri_compatible(): > > if (migration_needs_seekable_channel() && > !uri_supports_seeking(uri)) { > error_setg(errp, "Migration requires seekable transport (e.g. file)"); > compatible = false; > } Thanks! >>> +# >>> # 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: