I don't understand why you are using the @lines array at all, and without that your memory requirements go way down. The logic would be something like:

• %locks records currently open locks, with the key being the mutex address and the value being the input file line number where the lock was acquired
• if a 'locking' line is seen for a locked mutex, report it and overwrite the %locks entry with the newer lock
• if an 'unlocked' line is seen for a locked mutex, remove the %locks entry
• if an 'unlocked' line is seen for an unlocked mutex, report it
• when the input file is exhausted, report all remaining entries in %locks as "never unlocked"

Your existing code is close to that: remove the references to @lines; replace the definition of $count with:

  my $count = $.;  # input line number
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change the action for unlocking to:

  delete $locks{$address};
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and replace the final foreach (@lines) {print} with:

for (sort keys %locks) {
  Log 0, "ERROR: address $_ locked at line $locks{$_} but never unlock
+ed.";
}
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Hope this helps,

Hugo