migration_thread
qemu_savevm_state_setup
ram_save_setup
ram_init_all
ram_init_bitmaps
memory_global_dirty_log_start //全局标脏
MEMORY_LISTENER_CALL_GLOBAL(log_global_start, Forward);
.log_global_start = vhost_log_global_start,
vhost_migration_logvhost_dev_log_resize(dev, vhost_get_log_size(dev));