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Thu, 4 Jun 2020 11:31:46 +0000 (UTC) Date: Thu, 4 Jun 2020 13:31:45 +0200 From: Kevin Wolf To: Peter Krempa Subject: Re: [PATCH RFC v2 1/5] block: add bitmap-populate job Message-ID: <20200604113145.GE4512@linux.fritz.box> References: <20200514034922.24834-1-jsnow@redhat.com> <20200514034922.24834-2-jsnow@redhat.com> <20200604091231.GC4512@linux.fritz.box> <20200604091651.GF2995787@angien.pipo.sk> MIME-Version: 1.0 In-Reply-To: <20200604091651.GF2995787@angien.pipo.sk> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/04 01:31:23 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action 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: vsementsov@virtuozzo.com, Eduardo Habkost , qemu-block@nongnu.org, qemu-devel@nongnu.org, Markus Armbruster , Cleber Rosa , Max Reitz , John Snow Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 04.06.2020 um 11:16 hat Peter Krempa geschrieben: > On Thu, Jun 04, 2020 at 11:12:31 +0200, Kevin Wolf wrote: > > Am 18.05.2020 um 22:49 hat Eric Blake geschrieben: > > > > + > > > > + /* NB: new bitmap is anonymous and enabled */ > > > > + cluster_size = bdrv_dirty_bitmap_granularity(target_bitmap); > > > > + new_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp); > > > > + if (!new_bitmap) { > > > > + return NULL; > > > > + } > > > > > > This means if the guest writes to the disk while the job is ongoing, the > > > bitmap will be updated to mark that portion of the bitmap as set, even if it > > > was not allocated at the time the job started. But then again, the guest > > > writes are causing allocation, so this seems like the right thing to do. > > > > Is the target bitmap active at the same time, i.e. will it get the > > correct information only from new_bitmap or are the bits already set in > > it anyway? > > Yes, libvirt plans to use it with an active non-persistent bitmap which > will in subsequent steps be merged into others. The bitmap is added in > the same transaction. The bitmap must be active, because we need to wait > for the block jobs to finish before it becomes usable and thus can't > sequence in other operations until later. A lot of bitmap merging then, because the block job in this series already creates a temporary internal bitmap that is merged into the target bitmap on completion. But if the target bitmap is only libvirt's temporary bitmap to be merged to yet another bitmap, I wonder if this process shouldn't be simplified. Kevin