[libvirt] vm tunable memory and cgroup

hi,all 1. is there any relationship between cgroup and tunable memory ? if i adjust vm's memory, if cgroup has any responding action? <memory unit='KiB'>1048576</memory> <currentMemory unit='KiB'>524288</currentMemory> 2. it seems that the memory.limit_in_bytes of a vm in cgroup is twice over vm's assigned memory? addtional, blkio.sectors does not equal sectors calculated from inner vm. how limit_in_bytes, sectors are calculative? what is the relationship between them? thanks