Trying to benchmark SLURP versus other forms of Perl code

Get error "Substitution loop at c:/strawberry/perl/vendor/lib/File/Slurp.pm line 254

Following code works well to 600MB but over this size error occurs in step 3.

#!usr/bin/perl
use strict;
use File::Slurp qw( :all);
use Time::HiRes qw(gettimeofday tv_interval); 
#   get arguments for process
my $tmv0 = [gettimeofday];
my $fl_in = $ARGV[0];


#  reading records... step 1
open my $in_fh, '<', $fl_in or die $!;
my $s1=<$in_fh>;
print "$s1 from $fl_in \n";
my $numin=0;
while (<$in_fh>) {
 $numin++;
 }  
close $in_fh;
my $tmv1 = tv_interval($tmv0,[gettimeofday]);
print "  Test Step 1 Found $numin records at $tmv1\n";

###
### now using whole string... step 2
###
open my $in_fh, '<', $fl_in or die $!;
my $text_file = do { local $/; <$in_fh> }; 
close $in_fh;
my $tmv2 = tv_interval($tmv0,[gettimeofday])-$tmv1;
my $lenstr=length($text_file);
print "   Test Step 2 Found $lenstr bytes in $tmv2 seconds\n";

##
## Now slurp... step 3
##
$numin=0;

$text_file = read_file($fl_in);
$lenstr=length($text_file);
my $tmv3 = tv_interval($tmv0,[gettimeofday])-$tmv1-$tmv2;
print "   Test Step 3  Found $lenstr bytes in $tmv3 seconds\n";
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