On virtualization node holding 54 VMs, i only see around 18 machines, ie :
menu_cgroup_machine-slice_720d347c-bdbd-423e-ab8d-7f2a8245e446
Is there a setting that limitate ? if yes, how to increase it ?
Try to tweak it. Keep in mind, that this is not the number of visible cgroups, but the total number of cgroups that the plugin is examining (most of them are filtered out - look at matching options in the [plugin:cgroups] section).