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bh=ShIyOijF5hDb5xUYMjV46WkJwgk4IDv/i3PR+jIa9ZU=; b=JkxjvTefvaJYlEEc75G+eye1HfQz6zrb67e+epXbm22JBMRjHCBnW7t766AOsK+zqNryyC beXfKY2btwV6JaPRgXbbe84K84jGH/xWkDlx6EfvDj0pZrm+3uE7SNKyHHDcveYMmryhVE N19RDad0/v9yEF8FgCPHkvlrpDD5v68= X-MC-Unique: uaWFUDB4PteAADNMvSEd9w-1 From: peterx@redhat.com To: qemu-devel@nongnu.org Cc: Fabiano Rosas , =?UTF-8?q?Daniel=20P=20=2E=20Berrang=C3=A9?= , peterx@redhat.com Subject: [PATCH] migration/multifd: Document two places for mapped-ram Date: Fri, 1 Mar 2024 17:15:24 +0800 Message-ID: <20240301091524.39900-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.9 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.096, 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_H2=-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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1709284588919100003 Content-Type: text/plain; charset="utf-8" From: Peter Xu Add two documentations for mapped-ram migration on two spots that may not be extremely clear. Signed-off-by: Peter Xu Reviewed-by: Fabiano Rosas --- Based-on: <20240229153017.2221-1-farosas@suse.de> --- migration/multifd.c | 12 ++++++++++++ migration/ram.c | 8 +++++++- 2 files changed, 19 insertions(+), 1 deletion(-) diff --git a/migration/multifd.c b/migration/multifd.c index b4e5a9dfcc..2942395ce2 100644 --- a/migration/multifd.c +++ b/migration/multifd.c @@ -709,6 +709,18 @@ static bool multifd_send_cleanup_channel(MultiFDSendPa= rams *p, Error **errp) { if (p->c) { migration_ioc_unregister_yank(p->c); + /* + * An explicitly close() on the channel here is normally not + * required, but can be helpful for "file:" iochannels, where it + * will include an fdatasync() to make sure the data is flushed to + * the disk backend. + * + * The object_unref() cannot guarantee that because: (1) finalize() + * of the iochannel is only triggered on the last reference, and + * it's not guaranteed that we always hold the last refcount when + * reaching here, and, (2) even if finalize() is invoked, it only + * does a close(fd) without data flush. + */ qio_channel_close(p->c, &error_abort); object_unref(OBJECT(p->c)); p->c =3D NULL; diff --git a/migration/ram.c b/migration/ram.c index 1f1b5297cf..c79e3de521 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -4258,7 +4258,13 @@ static int ram_load_precopy(QEMUFile *f) switch (flags & ~RAM_SAVE_FLAG_CONTINUE) { case RAM_SAVE_FLAG_MEM_SIZE: ret =3D parse_ramblocks(f, addr); - + /* + * For mapped-ram migration (to a file) using multifd, we sync + * once and for all here to make sure all tasks we queued to + * multifd threads are completed, so that all the ramblocks + * (including all the guest memory pages within) are fully + * loaded after this sync returns. + */ if (migrate_mapped_ram()) { multifd_recv_sync_main(); } --=20 2.44.0