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Why does my script use much more memory when working with mod_perl?

I am 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 the GTop utility to measure memory ( recommended in the mod_perl book by Stas Beckman). GTop gives me confusing results.

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 does script memory grow so much in mod_perl ? Or maybe I'm measuring memory incorrectly? How do you view perl script memory?

Here is the script and its output (I added commas manually to make numbers easy to read)

  • Run from command line

      > perl simple.pl 

 size: 7,282688
 share: 2,027520
 diff: 5,255168

  • Running in mod_perl mode

      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";
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1 answer

I think when you run your script in mod_perl, you get the memory usage of the script, plus mod_perl, plus apache.

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