From 860c780a788f7c9e6269355cfd1b615fe8da9c07 Mon Sep 17 00:00:00 2001
From: Ole Tange <ole@tange.dk>
Date: Tue, 8 Nov 2022 18:11:57 +0100
Subject: [PATCH] swapout: Make it harder to compress memory.

---
 swapout/swapout | 44 ++++++++++++++++++++++++++++++++++----------
 1 file changed, 34 insertions(+), 10 deletions(-)

diff --git a/swapout/swapout b/swapout/swapout
index fe0ef73..642f4eb 100755
--- a/swapout/swapout
+++ b/swapout/swapout
@@ -2,6 +2,7 @@
 
 use strict;
 
+my $usegb = 1000*shift;
 my $timeout = shift || 10;
 
 my $giga = 2**30;
@@ -9,7 +10,7 @@ my $forks = 1;
 
 my $free;
 
-my $memtotal = int(
+my $memtotal = $usegb || int(
 	qx{ awk '/^(MemTotal):/ { sum += \$2} END { print sum }' /proc/meminfo }
     / 1024);
 
@@ -17,27 +18,37 @@ my $total = 1;
 
 # 1 MB random data so it is not compressed
 my $onemb = pack("L*", map { rand(2**32) } 1..(2**18));
-my ($missing, $sofar,$timediff, %buf, $pid,$shift);
+my ($thisround, $sofar,$timediff, %buf, $pid,$shift);
 do {
     my $start = time;
-    $free = int (
-	qx{ awk '/^((Swap)?Cached|MemFree|Buffers):/ { sum += \$2} END { print sum }' /proc/meminfo }
-	/ 1024);
+    $free =
+	int (
+	    qx{ awk '/^((Swap)?Cached|MemFree|Buffers):/ { sum += \$2} END { print sum }' /proc/meminfo }
+	    / 1024)
+	or
+	int (
+	    qx{ awk '/^MemAvailable:/ { sum += \$2 } END { print sum }' /proc/meminfo }
+	    / 1024);
     print "Free $free ";
     if($free <= 1) {
 	print "\nFree < 1\n";
 	exit(1);
     }
-    $total += int($free/100);
-    $missing = $total - $sofar;
-    for(1..$missing) {
+    # Use at most 1 GB per round
+    $thisround = min(1000,int($free/100));
+    $total += $thisround;
+    for(1..$thisround) {
 	# Shift every block 1 byte, so no blocks have the same content
 	$buf{$forks}{$total}{$_} = "x"x(++$shift) . $onemb;
+	if($shift > 4095) {
+	    # If shifted a full page: Recompute 1mb random
+	    $shift -= 4096;
+	    $onemb = pack("L*", map { rand(2**32) } 1..(2**18));
+	}
     }
-    $sofar = $total;
     $timediff = time - $start;
 
-    print "Chunk size: $missing Time for swapping: $timediff seconds. Total memory used: $total\n";
+    print "Chunk size: $thisround Time for swapping: $timediff seconds. Total memory used: $total\n";
     if($total * 1048576 > $forks * $giga) {
 	if($pid = fork()) {
 	    print "child spawn ",$forks,"\n";
@@ -50,3 +61,16 @@ do {
     }
 } until ($pid or $timediff > $timeout or $total > $memtotal);
 print "exit ",$forks,"\n";
+
+sub min {
+    # Returns:
+    #   Minimum value of array
+    my $min;
+    for (@_) {
+        # Skip undefs
+        defined $_ or next;
+        defined $min or do { $min = $_; next; }; # Set $_ to the first non-undef
+        $min = ($min < $_) ? $min : $_;
+    }
+    return $min;
+}