$ grep  "mymalloc='y'" hints/*
hints/hpux.sh:    $undef|false|[nN]*) usemymalloc='y' ;;
hints/ncr_tower.sh:usemymalloc='y'
hints/next_3.sh:#usemymalloc='y'
hints/next_4.sh:usemymalloc='y'
hints/sco_2_3_4.sh:usemymalloc='y'
hints/super-ux.sh:    usemymalloc='y'
hints/unicosmk.sh:'') usemymalloc='y'
hints/unicos.sh:    # usemymalloc='y'
hints/utekv.sh:usemymalloc='y'

##</code><code>##

use strict;
use warnings;

system "ps vp $$";

local $/;
open my $fd, "<", $ARGV[0] or die $!;
my $content = <$fd>;
system "ps vp $$";

undef $content;
system "ps vp $$";

##</code><code>##

$ dd if=/dev/zero of=zero.dat bs=8192 count=131072
131072+0 records in
131072+0 records out
1073741824 bytes (1.1 GB) copied, 8.40646 s, 128 MB/s

$ ls -lh zero.dat 
-rw-r--r-- 1 zwon zwon 1.0G 2010-03-06 13:23 zero.dat

$ perl -V | grep mymalloc
    usemymalloc=n, bincompat5005=undef

$ perl slurp_file.pl zero.dat
  PID TTY      STAT   TIME  MAJFL   TRS   DRS   RSS %MEM COMMAND
 3775 pts/1    S+     0:00      0     3 18140  2244  0.0 perl slurp_file.pl zero.dat
  PID TTY      STAT   TIME  MAJFL   TRS   DRS   RSS %MEM COMMAND
 3775 pts/1    S+     0:01      0     3 1066720 1050840 25.9 perl slurp_file.pl zero.dat
  PID TTY      STAT   TIME  MAJFL   TRS   DRS   RSS %MEM COMMAND
 3775 pts/1    R+     0:01      0     3 18140  2264  0.0 perl slurp_file.pl zero.dat

$ /opt/perl/5.10.1/bin/perl -V | grep mymalloc
    config_args='-des -Dusemymalloc -Dusethreads -Dprefix=/opt/perl/5.10.1'
    usemymalloc=y, bincompat5005=undef

$ /opt/perl/5.10.1/bin/perl slurp_file.pl zero.dat
  PID TTY      STAT   TIME  MAJFL   TRS   DRS   RSS %MEM COMMAND
 3792 pts/1    S+     0:00      0  1354 18925  2212  0.0 /opt/perl/5.10.1/bin/perl slurp_file.pl zero.dat
  PID TTY      STAT   TIME  MAJFL   TRS   DRS   RSS %MEM COMMAND
 3792 pts/1    S+     0:01      0  1354 1067505 1050812 25.9 /opt/perl/5.10.1/bin/perl slurp_file.pl zero.dat
  PID TTY      STAT   TIME  MAJFL   TRS   DRS   RSS %MEM COMMAND
 3792 pts/1    S+     0:01      0  1354 1067505 1050820 25.9 /opt/perl/5.10.1/bin/perl slurp_file.pl zero.dat