From 5b1d9bab2da4fca3a3caee97c430e5709cb32b7b Mon Sep 17 00:00:00 2001 From: Leonardo Bras Date: Fri, 13 May 2022 03:28:37 -0300 Subject: multifd: Implement zero copy write in multifd migration (multifd-zero-copy) Implement zero copy send on nocomp_send_write(), by making use of QIOChannel writev + flags & flush interface. Change multifd_send_sync_main() so flush_zero_copy() can be called after each iteration in order to make sure all dirty pages are sent before a new iteration is started. It will also flush at the beginning and at the end of migration. Also make it return -1 if flush_zero_copy() fails, in order to cancel the migration process, and avoid resuming the guest in the target host without receiving all current RAM. This will work fine on RAM migration because the RAM pages are not usually freed, and there is no problem on changing the pages content between writev_zero_copy() and the actual sending of the buffer, because this change will dirty the page and cause it to be re-sent on a next iteration anyway. A lot of locked memory may be needed in order to use multifd migration with zero-copy enabled, so disabling the feature should be necessary for low-privileged users trying to perform multifd migrations. Signed-off-by: Leonardo Bras Reviewed-by: Peter Xu Reviewed-by: Daniel P. Berrangé Message-Id: <20220513062836.965425-9-leobras@redhat.com> Signed-off-by: Dr. David Alan Gilbert --- migration/socket.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'migration/socket.c') diff --git a/migration/socket.c b/migration/socket.c index 3754d8f72c..4fd5e85f50 100644 --- a/migration/socket.c +++ b/migration/socket.c @@ -79,8 +79,9 @@ static void socket_outgoing_migration(QIOTask *task, trace_migration_socket_outgoing_connected(data->hostname); - if (migrate_use_zero_copy_send()) { - error_setg(&err, "Zero copy send not available in migration"); + if (migrate_use_zero_copy_send() && + !qio_channel_has_feature(sioc, QIO_CHANNEL_FEATURE_WRITE_ZERO_COPY)) { + error_setg(&err, "Zero copy send feature not detected in host kernel"); } out: -- cgit v1.2.3-55-g7522