[libvirt] virDomainMemoryStats call

Hi, Is the array mstats returned by virDomainMemoryStats call cummulative or snapshot of the counter at that particular time ? I was of the opinion that is cummulative like the /proc counters but this counter seems to go backwards ie next snapshot value is less than the current one which makes me think these are snapshot values . I'm using RHEL 6.3 libvirt version 0.9.10. Regards, Navin