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[174.91.135.175]) by smtp.gmail.com with ESMTPSA id 4sm1503554qkj.119.2021.03.23.07.54.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Mar 2021 07:54:58 -0700 (PDT) Date: Tue, 23 Mar 2021 10:54:57 -0400 From: Peter Xu To: Andrey Gruzdev Subject: Re: [PATCH v1 1/3] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread Message-ID: <20210323145457.GC6486@xz-x1> References: <20210319145249.425189-1-andrey.gruzdev@virtuozzo.com> <20210319145249.425189-2-andrey.gruzdev@virtuozzo.com> <20210322201716.GG16645@xz-x1> <2fb49f83-e31c-8c93-50b7-833026b06518@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <2fb49f83-e31c-8c93-50b7-833026b06518@virtuozzo.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, RCVD_IN_MSPIKE_H4=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juan Quintela , Markus Armbruster , David Hildenbrand , qemu-devel@nongnu.org, "Dr . David Alan Gilbert" , Paolo Bonzini , Den Lunev Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Mar 23, 2021 at 10:51:57AM +0300, Andrey Gruzdev wrote: > On 22.03.2021 23:17, Peter Xu wrote: > > On Fri, Mar 19, 2021 at 05:52:47PM +0300, Andrey Gruzdev wrote: > > > Added missing qemu_fflush() on buffer file holding precopy device state. > > > Increased initial QIOChannelBuffer allocation to 512KB to avoid reallocs. > > > Typical configurations often require >200KB for device state and VMDESC. > > > > > > Signed-off-by: Andrey Gruzdev > > > --- > > > migration/migration.c | 4 +++- > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/migration/migration.c b/migration/migration.c > > > index ca8b97baa5..32b48fe9f5 100644 > > > --- a/migration/migration.c > > > +++ b/migration/migration.c > > > @@ -3812,7 +3812,7 @@ static void *bg_migration_thread(void *opaque) > > > * with vCPUs running and, finally, write stashed non-RAM part of > > > * the vmstate from the buffer to the migration stream. > > > */ > > > - s->bioc = qio_channel_buffer_new(128 * 1024); > > > + s->bioc = qio_channel_buffer_new(512 * 1024); > > > qio_channel_set_name(QIO_CHANNEL(s->bioc), "vmstate-buffer"); > > > fb = qemu_fopen_channel_output(QIO_CHANNEL(s->bioc)); > > > object_unref(OBJECT(s->bioc)); > > > @@ -3866,6 +3866,8 @@ static void *bg_migration_thread(void *opaque) > > > if (qemu_savevm_state_complete_precopy_non_iterable(fb, false, false)) { > > > goto fail; > > > } > > > + qemu_fflush(fb); > > What will happen if the vmstates are bigger than 512KB? Would the extra data > > be dropped? > > No, the buffer shall be reallocated and the original content shall be kept. Oh right.. Would you comment above qemu_fflush() about it (maybe also move it right before the call to qemu_put_buffer)? Otherwise it indeed looks more like an optimization rather than a bugfix. For the long term I think we'd better have a helper: qemu_put_qio_channel_buffer(QEMUFile *file, QIOChannelBuffer *bioc) So as to hide this flush operation, which is tricky. We'll have two users so far: bg_migration_completion colo_do_checkpoint_transaction IMHO it'll be nicer if you'd do it in this patch altogether! Thanks, -- Peter Xu