Maybe fragmentation from extending the stack is using up a lot of memory. Try to avoid putting the entire file on the stack, and pre-extending its destination: 

my @lines;
$#lines = 12_000_000;
@lines = ();
push @lines, $_ while <IN>;

[download]

Note that shuffle already exists in List::Util.

Update: Fixed bug.

In reply to Re: mem usage by ikegami
in thread mem usage by halfcountplus

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