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 941FDC00A8F for ; Tue, 24 Oct 2023 18:36:37 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qvMFu-0004Bp-8X; Tue, 24 Oct 2023 14:35:54 -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 1qvMFs-0004Aj-88 for qemu-devel@nongnu.org; Tue, 24 Oct 2023 14:35:52 -0400 Received: from smtp-out2.suse.de ([2001:67c:2178:6::1d]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1qvMFm-0002O9-MD for qemu-devel@nongnu.org; Tue, 24 Oct 2023 14:35:51 -0400 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id EBD991FE9F; Tue, 24 Oct 2023 18:35:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1698172543; h=from:from:reply-to: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=eL79aGGX9xCM91MFhc9M7/97a6nA62VQu6IeBDoQOag=; b=XPr76rSHqx70Anv7+dFQMAi78P9INxqH3nT7xRByCi/C7jdfv4c4SklXkV0Nnyy+kJBBpL kND/jF2IarzBq+TPXl5nqEi8iCUhj996PoI8nlgB4NTGzESmO/8naWYWFpXNZlJkwPCOtj /VEMw0J0rah3PuLQr4oHvql0dLsrraU= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1698172543; h=from:from:reply-to: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=eL79aGGX9xCM91MFhc9M7/97a6nA62VQu6IeBDoQOag=; b=lmOJZh9puqtYzw2yqaRV5VKmcrBZjBNKKxYjUdo4F4Mi0CkIqulDKNRtFFa9gcHLj0SdXP JcVtFntFpBGhCEAg== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 7F2191391C; Tue, 24 Oct 2023 18:35:43 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id BXDHEn8OOGXUJwAAMHmgww (envelope-from ); Tue, 24 Oct 2023 18:35:43 +0000 From: Fabiano Rosas To: Markus Armbruster 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 In-Reply-To: <87fs20vb2p.fsf@pond.sub.org> References: <20231023203608.26370-1-farosas@suse.de> <20231023203608.26370-15-farosas@suse.de> <87fs20vb2p.fsf@pond.sub.org> Date: Tue, 24 Oct 2023 15:35:41 -0300 Message-ID: <87zg07dg1u.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=2001:67c:2178:6::1d; envelope-from=farosas@suse.de; helo=smtp-out2.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, 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 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*. >> + >> 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 > Which transports are seekable? > The ones that implement QIO_CHANNEL_FEATURE_SEEKABLE. Currently only QIOChannelFile. > 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; } >> +# >> # 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: