From: Eric Hodel <drbrain@...7.net>
Date: 2006-11-06T07:44:27+09:00
Subject: Re: Garbage collection/memory unfreed problem

On Nov 2, 2006, at 9:55 PM, Mark Noworolski wrote:

> It appears that the ruby garbage collector is not freeing up unused
> memory on my linux machine, but IS on my windows machine... I'm  
> baffled
> and troubled. Any advice would be appreciated...
>
> Using the attached test script, in linux I observe the VMRSS start at
> around 1.5Meg, then go up to ~20Meg by iteration 3 or 4, and sit there
> for the remaining iterations. Then once the t array goes out of  
> scope, I
> see it drop by a few meg. The GC.start only drops apparent memory
> consumption to ~14Meg.
>
> Meanwhile, on windows XP, I see it increase to around 20Meg, then sit
> around there until the GC.free, which brings it back down to around
> 5Meg, close to the starting point.
>
> Can anybody explain the difference here? Is the 14meg _really_
> unavailable to the OS in linux?

Ruby's garbage collector is conservative and walks the stack looking  
for pointers into the heap.  If it finds a possible pointer to the  
heap the referenced memory will not be reclaimed.  This can happen  
even if you've returned from a method that referenced a large object.

> -------------
> class Grab
>   def initialize
>     @myhash={}
>     0.upto(100000) {|i| @myhash[i]="#{i} Im a part of a hash"}
>   end
> end
>
> def memuse
>   #IO.read("/proc/#{Process.pid}/status") =~ /VmSize.* (\d+) k/
>   "Hi"
> end
>
> puts "Mem before anything: #{memuse}"
> sleep 10;
> 0.upto(10) do |x|
>   t||=Array.new
>   t[x]=Grab.new
> puts "Mem in scope #{x}: #{memuse}"
> sleep 1;
> end
> puts "mem out of scope #{memuse}"
> sleep 10;
> GC.start
> puts "Mem after GC: #{memuse}"
> sleep 10;

-- 
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net
This implementation is HODEL-HASH-9600 compliant

http://trackmap.robotcoop.com