Forget using Perl's Windows fork emulation. It leaks like a sieve.

See how you get on with this. On my system it settles down to a steady state memory usage after a few cycles:

#! perl -sw
use 5.010;
use strict;
use threads ( stack_size => 4096 );

while( 1 ) {
    async( \&get_data_and_go )->detach;
    sleep 5; ## Go get every 5 seconds
}

sub get_data_and_go {
    my $tid = threads->tid;
    require LWP::Simple; ## Requiring prevent CLONE leaks.
    
    ##does some webpage stuff and exits
    my $bytes= length(  LWP::Simple::get( 'http://www.yahoo.com' ) );
    say "$tid : Got $bytes";

    sleep rand 10; ## Simulated variable processing time
    say "$tid : done";
    return 0;
};
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