How about anchoring the newline at the start? 
while ($mmap =~ m/\n?(.*$pat.*\n)/omg) {

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Note that .* is equivalent to [^\n]* if you're not using /s. I added the * at the end, because it fits the /dict/words lookup.

Removing the ? at the beginning makes it even faster, but then you need to handle the first line specially.

"What should it profit a man, if he should win a flame war, yet lose his cool?"

In reply to Re: Surprisingly poor regex performance by Joost
in thread Surprisingly poor regex performance by sgifford

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