Documentation: memcg: future proof hierarchical statistics documentation

hierarchical_memsw_limit - # of bytes of memory+swap limit with regard to

			hierarchy under which memory cgroup is.

total_cache		- sum of all children's "cache"

total_rss		- sum of all children's "rss"

total_mapped_file	- sum of all children's "cache"

total_pgpgin		- sum of all children's "pgpgin"

total_pgpgout		- sum of all children's "pgpgout"

total_swap		- sum of all children's "swap"

total_inactive_anon	- sum of all children's "inactive_anon"

total_active_anon	- sum of all children's "active_anon"

total_inactive_file	- sum of all children's "inactive_file"

total_active_file	- sum of all children's "active_file"

total_unevictable	- sum of all children's "unevictable"

total_<counter>		- # hierarchical version of <counter>, which in

			addition to the cgroup's own value includes the

			sum of all hierarchical children's values of

			<counter>, i.e. total_cache

# The following additional stats are dependent on CONFIG_DEBUG_VM.