Hi Monks, I know this theme 50069 was discussed in 2001, but does anybody has deep information on how to influence the garbage collector, to free memory (in the sense of give it back to the OS)? Let me show: 
{
    my $foo = 'X' x 100000000;
    getc;
}
undef $foo;
my $foo = "";
getc;

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At the first prompt (via ps auxwf output): 
user   12310  2.1  4.8 211000 197024 pts/2
                   
At the second prompt:
user   12310  1.2  4.8 211000 197028 pts/2

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Now, what I wanted to show: - the memory allocated for $foo is not released. What I read on several mailing-lists is that the optimizer does not return the memory to the OS, in the hope that the same variable will be used again. But what I'm missing is some kind of a 'free' statement in Perl, which definitely returns memory (and I not know yet, undef seems not to help).
Let me show another example: 
$foo = 'X' x 100000000;
getc;
undef $foo;
getc;
$foo2 = 'X' x 100000000;
getc;

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gives (again output from 'ps auxwf'): 
user   15185 18.0  4.8 211000 197020 pts/5
user   15185  5.0  2.4 113340 99364 pts/5
user   15185  4.3  7.2 308660 294684 pts/5

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As you see some RAM is given back to the OS (~50%, (99364/197020)) . BUT: I would expect that the Perl virtual machine (memory management) reuses the allocated RAM from $foo for $foo2.
As you see $foo is not used anymore in the program context, but the memory management still holds some RAM for it present (I mean why ?).
(I'm using perl 5.10.0 on OpenSUSE 11.0)

In reply to Perl Garbage Collection, again by pkirsch

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