I have to open up 300+ connections ... the process size grows to 2-3G

Hm. The following code starts 300 threads, each of which opens a connection to a local echo+1 server. The total memory usage is under 700MB:

#! perl -slw
use strict;
use IO::Socket;
use Time::HiRes qw[ sleep ];
use threads stack_size => 4096;  ## Tip: This significantly reduces th
+reads memory usage 

$\ = $/ = chr(13) . chr(10);

sub connection {

    my $svr;
    do {
        $svr = IO::Socket::INET->new( 'localhost:12345' );
    } until $svr;
    
    while( 1 ) {
        my $msg = int( rand 2**30 );
        my $reply;

        print $svr $msg;
        $reply = <$svr> until $reply;
        chomp $reply;
        warn 'Mismatch' unless $msg + 1 == $reply;
        sleep 0.001;
    }
}

async( \&connection )->detach for 1 .. 300;

sleep 1000;
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The other memory saving tip is: only use those packages you need within your threads, before creating them. Load (require) anything that you only need in main after you've created your threads.

The threaded echo+1 server for your testing:

#! perl -slw
use strict;
use threads stack_size => 4096;
use IO::Socket;

$\ = $/ = chr(13).chr(10);

my $lsn = IO::Socket::INET->new( Reuse => 1, Listen => 1e6, LocalPort 
+=> 12345 )
    or die "Server failed to create listener: $^E";
print "Server listener created";
while( my $client = $lsn->accept ) {
    print "Server accepting client connection";
    async {
        while( my $in = <$client> ) {
            chomp $in;
            print $client $in + 1;
            printf "\rServer echoing client input: '%s'", $in;
        }
        print "Server shutting down";
        shutdown $client, 2;
        close $client;
    }->detach;
}
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