Re: [PATCH v4 2/4] mm/util.c: make vm_memory_committed() more accurate

[Andi Kleen]

> Its time cost is about 800 nanoseconds on a 2C/4T platform and
> 2~3 microseconds on a 2S/36C/72T server in normal case, and in
> worst case where vm_committed_as's spinlock is under severe
> contention, it costs 30~40 microseconds for the 2S/36C/72T sever,

This will be likely 40-80us on larger systems, although the overhead
is often non linear so it might get worse.

> which should be fine for its only two users: /proc/meminfo and
> HyperV balloon driver's status trace per second.

There are some setups who do frequent sampling of /proc/meminfo
in the background.  Increased overhead could be a problem for them.
But not proposing a change now. If someone complains have to 
revisit I guess, perhaps adding a rate limit of some sort.

-Andi