From: KUBO Takehiro <kubo@...>
Date: 2009-07-26T21:25:07+09:00
Subject: Re: [C/Linux] How to get amount of allocated memory from within a 	process (heap size)

On Fri, Jul 24, 2009 at 5:28 PM, Gennady
Bystritsky<Gennady.Bystritsky@quest.com> wrote:
> What would be a good way to determine the current heap size (VSZ) for a process on Linux?
>
> I always used sbrk(0) for that, which used to return the top of the heap. However recently, to my dismay, I discovered that it does not work on Linux -- I successfully malloc()-ed 1GB, could confirm it with "ps -o pid,vsz,args", and yet sbrk(0) always returns the same value as right in the beginning.

It this topic related to ruby?

Well, type "man malloc" and look for MMAP_THRESHOLD.
Increasing MMAP_THRESHOLD large enough forces malloc() to use brk()
instead of mmap(). sbrk(0) doesn't care mmap()-ed memory.