Sorry for OT'ing your post, but I thought an example of mmap on *nix, tested in Linux, could be useful for those lucky linux users:

use strict;
use warnings;
use Fcntl;
use Inline C => Config => LIBS => '', BUILD_NOISY => 1;
use Inline C => <<'END_OF_C_CODE';

#include <sys/mman.h>
#include <stdio.h>
#include <errno.h>

int unmap_region(void *m, int sz){
    if( munmap(m, sz) != 0 ){
        fprintf(stderr, "unmap_region() : error, call to munmap() has 
+failed for memory address %p and size %ld : %s\n", m, sz, strerror(er
+rno));
        return 0; // failed
    }
    return 1; // success
}
void *map_region(int fd, int sz){
        char *map = (char *)mmap(NULL, sz, PROT_READ|PROT_WRITE, MAP_F
+ILE|MAP_SHARED, fd, 0);
        if (map == MAP_FAILED){
        fprintf(stderr, "map has failed for size %ld : %s\n", sz, stre
+rror(errno));
        return (void *)NULL; // failed
    }
    return map; // success
}
END_OF_C_CODE

my $test_file = 'test_mmap.bin';

sysopen(my $fh, $test_file, O_RDWR|O_CREAT|O_TRUNC)
  or die "can't open file '$test_file' : $!";
binmode $fh;
my $size = 4096;
my $addr = map_region(fileno($fh), $size)
  or die "mmap failed!!:  $^E ";

my $test_str = "Hello Linux mmap!";
syswrite($fh, $test_str);

unmap_region($addr, $size) or die "fail to unmap";

close($fh);

open($fh, '<', $test_file) or die "failed to open file '$test_file'/2,
+ $!";
my $contents;
{ local $/ = undef; $contents = <$fh> } close $fh;
print "Sucess, contents of the mmap'ed file '$test_file':\n${contents}
+\n--end contents.\n";
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