How to get system available memory and some process memory usage through system call or API

[Tao, Liu]

Hi
   I want to get system available memory and memory usage of one
precess(known Pid). Now I read /proc/meminfo and /proc/$pid/stat to
get above data.
   And my question is:
   1 Is there system call or API to get above data?
   2 Linux kernel add "MemAvailable" to "/proc/meminfo" in 3.14, but I
use kernel 3.10. Can I calculate "MemAvailable" through data read from
/proc/meminfo in kernel 3.10? How?

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Best Wishes,

Tao, Liu