How much memory is really free?

[Xiangfei Jia <xjianz@xxxxxxxxx>]

I know that some part of memory is free, but they are used in caches to
optimise the performance when the system needs to allocate more memory.
And, dentry caches and disk buffer_head are used to minimise disk
access. SO, give the current mem info from "cat /proc/meminfo", how
sould I calculate how much memory is really free creently in the system?

> cat /proc/meminfo
MemTotal:      1017848 kB
MemFree:       10380 kB
Buffers:          37480 kB
Cached:         149868 kB

Can I just assume that 70% of un-used memory (un-used=mem_total -
buffers - cached) is free, without actually causing the system to
swapping?

Thanks in advance!

Fei