From: "Marshall T. Vandegrift" <llasram@...>
Date: 2006-08-30T12:13:52+09:00
Subject: Re: Can Anyone Explain This Memory Leak?

I posted this earlier, but gmane seems to have snarfed it.  Apologies if it
shows up twice.

gwtmp01@mac.com writes:

> Run your code under a process trace program such as ktrace (Mac OS X).  You
> should be able to easily grep the resulting dump for system calls that
> *actually* return memory to the OS.  Just because free is called doesn't mean
> that the memory allocator has actually notified the kernel that it no longer
> needs that huge hunk of memory.

I posted some graphs in an earlier message:

    http://article.gmane.org/gmane.comp.lang.ruby.general/168484

But I now have some prettier versions from 2-hour runs (apologies for the image
sizes):

    http://llasram.wuli.nu/mutex.png
    http://llasram.wuli.nu/sync.png

In these graphs the red line represents the amount of memory Ruby is allocating
from the heap.  The blue-green regions represent where those allocations are
coming from in byte offsets from the base of the heap.  These graphs no longer
have the brk() line indicating the end of the heap because (on Linux anyway) it
exactly tracks the highest allocated heap memory address.

This visually demonstrates that the heap is becoming highly fragmented with
both scripts, albeit worse with 'mutex.rb'.

> I'm guessing you'll look for calls to munmap or something similar.

At least on Linux, the allocation pattern used by these scripts never causes
the heap implementation to get system memory via m/unmap() (as you can see
visually in my graphs by how the amount ruby allocates using malloc() never
goes beyond the size of the heap, even during peak allocation periods).

-Marshall