Question

I’m trying to learn how to profile perl memory.

I have a very simple Perl hello-world script and I want to know its size in memory.

I use GTop utility to measure the memory (recommended in mod_perl book by Stas Beckman).
GTop provides the results that confuse me.

When I run the script from the command line GTop says: 7M.

When I run it under mod_perl, GTop says: 54M.

Why so much?!

Why script memory grows so much under mod_perl?
Or maybe I measure the memory in a wrong way?
How do you profile perl script memory?

Here are the script and its output (I have added commas manually to easily read the numbers)

1. Run from command-line

   > perl simple.pl 
   
   size: 7,282688
   share: 2,027520
   diff: 5,255168
   

2. Run under mod_perl

   size: 54,878208
   share: 4,661248
   diff: 50,216960
   

Script simple.pl

#!/usr/bin/perl

use strict;
use warnings;
use CGI ();

my $cgi = CGI->new;

print $cgi->header('text/plain');

use GTop;

print "Hello, world!\n";
my $m = GTop->new->proc_mem($$);
print "size: ".$m->size."\n";
print "share: ".$m->share."\n";
my $diff = $m->size - $m->share;
print "diff: $diff\n";

Answer 1

I guess when you run your script under mod_perl, you get your script’s memory usage, plus mod_perl’s, plus apache’s.

See also the answers to these questions:

• How can I programmatically determine my Perl program’s memory usage under Windows?
• Perl memory usage profiling and leak detection?