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 C1A8EC5475B for ; Fri, 8 Mar 2024 07:42:16 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1riUro-0005DX-T5; Fri, 08 Mar 2024 02:42:09 -0500 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 1riUrj-0005AJ-Nq for qemu-devel@nongnu.org; Fri, 08 Mar 2024 02:42:04 -0500 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 1riUrd-0007wB-Cv for qemu-devel@nongnu.org; Fri, 08 Mar 2024 02:41:58 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1709883716; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=5uEh34mEbYn8guicwzp3Lpm2Ygc2hj4Le8h2zq8iJEg=; b=htjG23hTAuoqBvwFbOQSKBdk4BvOmGx1dpUanISoAEp3de0lMrc4nlI7k5aRTGtCP5NmGk wN62NBgiu7Y691cDGmoKpQ+YtxjhxhkqtaRgUWL0t47ynK1yi/go8mdADfAJA5vthezE1z NuNPWrhF0Fxkdy69OGKVuh8GXZoa7s4= 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-652-bqwS1JXCNmuYxP6dJak4mg-1; Fri, 08 Mar 2024 02:41:53 -0500 X-MC-Unique: bqwS1JXCNmuYxP6dJak4mg-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 E44CB18653A2; Fri, 8 Mar 2024 07:41:52 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.3]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 73FA32022AB6; Fri, 8 Mar 2024 07:41:52 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 4B61121E6A24; Fri, 8 Mar 2024 08:41:51 +0100 (CET) From: Markus Armbruster To: Fiona Ebner Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, eblake@redhat.com, hreitz@redhat.com, kwolf@redhat.com, vsementsov@yandex-team.ru, jsnow@redhat.com, f.gruenbichler@proxmox.com, t.lamprecht@proxmox.com, mahaocong@didichuxing.com, xiechanglong.d@gmail.com, wencongyang2@huawei.com Subject: Re: [PATCH v2 2/4] mirror: allow specifying working bitmap In-Reply-To: <20240307134711.709816-3-f.ebner@proxmox.com> (Fiona Ebner's message of "Thu, 7 Mar 2024 14:47:09 +0100") References: <20240307134711.709816-1-f.ebner@proxmox.com> <20240307134711.709816-3-f.ebner@proxmox.com> Date: Fri, 08 Mar 2024 08:41:51 +0100 Message-ID: <877cid6ugw.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.583, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 Fiona Ebner writes: > From: John Snow > > for the mirror job. The bitmap's granularity is used as the job's > granularity. > > The new @bitmap parameter is marked unstable in the QAPI and can > currently only be used for @sync=3Dfull mode. > > Clusters initially dirty in the bitmap as well as new writes are > copied to the target. > > Using block-dirty-bitmap-clear and block-dirty-bitmap-merge API, > callers can simulate the three kinds of @BitmapSyncMode (which is used > by backup): > 1. always: default, just pass bitmap as working bitmap. > 2. never: copy bitmap and pass copy to the mirror job. > 3. on-success: copy bitmap and pass copy to the mirror job and if > successful, merge bitmap into original afterwards. > > When the target image is a fresh "diff image", i.e. one that was not > used as the target of a previous mirror and the target image's cluster > size is larger than the bitmap's granularity, or when > @copy-mode=3Dwrite-blocking is used, there is a pitfall, because the > cluster in the target image will be allocated, but not contain all the > data corresponding to the same region in the source image. > > An idea to avoid the limitation would be to mark clusters which are > affected by unaligned writes and are not allocated in the target image > dirty, so they would be copied fully later. However, for migration, > the invariant that an actively synced mirror stays actively synced > (unless an error happens) is useful, because without that invariant, > migration might inactivate block devices when mirror still got work > to do and run into an assertion failure [0]. > > Another approach would be to read the missing data from the source > upon unaligned writes to be able to write the full target cluster > instead. > > But certain targets like NBD do not allow querying the cluster size. > To avoid limiting/breaking the use case of syncing to an existing > target, which is arguably more common than the diff image use case, > document the limiation in QAPI. > > This patch was originally based on one by Ma Haocong, but it has since > been modified pretty heavily, first by John and then again by Fiona. > > [0]: https://lore.kernel.org/qemu-devel/1db7f571-cb7f-c293-04cc-cd856e060= c3f@proxmox.com/ > > Suggested-by: Ma Haocong > Signed-off-by: Ma Haocong > Signed-off-by: John Snow > [FG: switch to bdrv_dirty_bitmap_merge_internal] > Signed-off-by: Fabian Gr=C3=BCnbichler > Signed-off-by: Thomas Lamprecht > [FE: rebase for 9.0 > get rid of bitmap mode parameter > use caller-provided bitmap as working bitmap > turn bitmap parameter experimental] > Signed-off-by: Fiona Ebner [...] > diff --git a/qapi/block-core.json b/qapi/block-core.json > index 59d75b0793..4859fffd48 100644 > --- a/qapi/block-core.json > +++ b/qapi/block-core.json > @@ -2191,6 +2191,18 @@ > # destination (all the disk, only the sectors allocated in the > # topmost image, or only new I/O). > # > +# @bitmap: The name of a bitmap to use as a working bitmap for > +# sync=3Dfull mode. This argument must be not be present for other > +# sync modes and not at the same time as @granularity. The > +# bitmap's granularity is used as the job's granularity. When > +# the target is a diff image, i.e. one that should only contain > +# the delta and was not synced to previously, the target's > +# cluster size must not be larger than the bitmap's granularity. > +# For a diff image target, using copy-mode=3Dwrite-blocking should > +# not be used, because unaligned writes will lead to allocated > +# clusters with partial data in the target image! The bitmap > +# will be enabled after the job finishes. (Since 9.0) That's a lot of restrictions and caveats. Okay as long as the thing remains experimental, I guess. > +# > # @granularity: granularity of the dirty bitmap, default is 64K if the > # image format doesn't have clusters, 4K if the clusters are > # smaller than that, else the cluster size. Must be a power of 2 > @@ -2228,12 +2240,18 @@ > # disappear from the query list without user intervention. > # Defaults to true. (Since 3.1) > # > +# Features: > +# > +# @unstable: Member @bitmap is experimental. > +# > # Since: 1.3 > ## > { 'struct': 'DriveMirror', > 'data': { '*job-id': 'str', 'device': 'str', 'target': 'str', > '*format': 'str', '*node-name': 'str', '*replaces': 'str', > - 'sync': 'MirrorSyncMode', '*mode': 'NewImageMode', > + 'sync': 'MirrorSyncMode', > + '*bitmap': { 'type': 'str', 'features': [ 'unstable' ] }, > + '*mode': 'NewImageMode', > '*speed': 'int', '*granularity': 'uint32', > '*buf-size': 'int', '*on-source-error': 'BlockdevOnError', > '*on-target-error': 'BlockdevOnError', > @@ -2513,6 +2531,18 @@ > # destination (all the disk, only the sectors allocated in the > # topmost image, or only new I/O). > # > +# @bitmap: The name of a bitmap to use as a working bitmap for > +# sync=3Dfull mode. This argument must be not be present for other > +# sync modes and not at the same time as @granularity. The > +# bitmap's granularity is used as the job's granularity. When > +# the target is a diff image, i.e. one that should only contain > +# the delta and was not synced to previously, the target's > +# cluster size must not be larger than the bitmap's granularity. > +# For a diff image target, using copy-mode=3Dwrite-blocking should > +# not be used, because unaligned writes will lead to allocated > +# clusters with partial data in the target image! The bitmap > +# will be enabled after the job finishes. (Since 9.0) > +# > # @granularity: granularity of the dirty bitmap, default is 64K if the > # image format doesn't have clusters, 4K if the clusters are > # smaller than that, else the cluster size. Must be a power of 2 > @@ -2548,6 +2578,10 @@ > # disappear from the query list without user intervention. > # Defaults to true. (Since 3.1) > # > +# Features: > +# > +# @unstable: Member @bitmap is experimental. > +# > # Since: 2.6 > # > # Example: > @@ -2562,6 +2596,7 @@ > 'data': { '*job-id': 'str', 'device': 'str', 'target': 'str', > '*replaces': 'str', > 'sync': 'MirrorSyncMode', > + '*bitmap': { 'type': 'str', 'features': [ 'unstable' ] }, > '*speed': 'int', '*granularity': 'uint32', > '*buf-size': 'int', '*on-source-error': 'BlockdevOnError', > '*on-target-error': 'BlockdevOnError', Acked-by: Markus Armbruster [...]