#!/usr/bin/perl
# Usage:
# ./chewmem.pl <MiB>

# Description:
# This will create a character array requiring "MiB" actual memory.
# Summarize high-level memory usage.

# Ideally we can demonstate creating larger and larger
# successful memory allocations until Avail is near 0.
# It is very likely to trigger OOM Killer or cause reset
# if we run completely out of memory.

use warnings;
use strict;
use POSIX qw(strftime);

sub show_memusage() {
	our $count;
 	$::count++; $::count %= 15;

	my $Ki = 1024.0;
	my ($MemTotal, $MemFree, $Buffers, $Cached, $CommitLimit, $Committed_AS, $Slab, $SReclaimable);
	# Process all entries of MEMINFO
	my $file = '/proc/meminfo';
	open(FILE, $file) || die "Cannot open file: $file  ($!)";
	MEMINFO_LOOP: while($_ = <FILE>) {
		s/[\0\e\f\r\a]//g; chomp; # strip control characters if any
		last MEMINFO_LOOP if (/^\s*$/); # end at blank-line
		if (/\bMemTotal:\s+(\d+)\s+kB/) {
			$MemTotal = $1; next MEMINFO_LOOP;
		}
		if (/\bMemFree:\s+(\d+)\s+kB/) {
			$MemFree = $1; next MEMINFO_LOOP;
		}
		if (/\bBuffers:\s+(\d+)\s+kB/) {
			$Buffers = $1; next MEMINFO_LOOP;
		}
		if (/\bCached:\s+(\d+)\s+kB/) {
			$Cached = $1; next MEMINFO_LOOP;
		}
		if (/\bCommitLimit:\s+(\d+)\s+kB/) {
			$CommitLimit = $1; next MEMINFO_LOOP;
		}
		if (/\bCommitted_AS:\s+(\d+)\s+kB/) {
			$Committed_AS = $1; next MEMINFO_LOOP;
		}
		if (/\bSlab:\s+(\d+)\s+kB/) {
			$Slab = $1; next MEMINFO_LOOP;
		}
		if (/\bSReclaimable:\s+(\d+)\s+kB/) {
			$SReclaimable = $1; next MEMINFO_LOOP;
		}
	}
	close(FILE);

	my $Avail_MiB  = ($MemFree + $Cached + $Buffers + $SReclaimable)/$Ki;
	my $Strict_MiB = ($CommitLimit - $Committed_AS)/$Ki;
	my $now = strftime "%Y-%m-%d %H:%M:%S", localtime();
	if ($::count == 1) {
		printf "%19s %6s %6s %6s %6s %6s %6s %6s %6s %6s\n",
			'yyyy-mm-dd hh:mm:ss', 'Tot', 'Free', 'Ca', 'Buf', 'Slab', 'CAS', 'CLim', 'Avail', 'Strict';
	}
	printf "%19s %6.1f %6.1f %6.1f %6.1f %6.1f %6.1f %6.1f %6.1f %6.1f\n",
		$now, $MemTotal/$Ki, $MemFree/$Ki, $Cached/$Ki, $Buffers/$Ki, $Slab/$Ki,
		$Committed_AS/$Ki, $CommitLimit/$Ki, $Avail_MiB, $Strict_MiB;
}

#-------------------------------------------------------------------------------
# MAIN PROGRAM
# Autoflush output
select(STDERR);
$| = 1;
select(STDOUT); # default
$| = 1;

my $MiB = $ARGV[0] ||=0.0;
my $A = "A" x (1024*1024*$MiB/2);
print "Allocating $MiB MiB character array.\n";
while(1) {
	sleep(1);
	show_memusage();
}
exit 0;

1;