libgtop2 provides an API between GTK+ applications and the kernel-structures.
It returns swap-information, but forgets to multiple it by getpagesize().

Fix: Add this file as files/patch-sysdeps::freebsd::swap.c
How-To-Repeat: 
Install sysutils/gnomesystemsmonitor and check the swap-size.
Or run this:

#include <stdio.h>
#include <glibtop.h>
#include <glibtop/swap.h>

void swap(void) {
        glibtop_swap swap;

	glibtop_get_swap(&swap);
	printf("SWAP\n");
	printf("total: %lld\n",swap.total);
	printf("used : %lld\n",swap.used );
	printf("free : %lld\n",swap.free );
}

int main(void) {
        glibtop_init();
	swap();
}

gcc -Wall -I/usr/local/include/libgtop-2.0 -L/usr/local/lib -o a a.c -lgtop-2.0 -lgtop_common-2.0 -lgtop_suid_common-2.0 -lgtop_sysdeps-2.0 -lgtop_names-2.0 -lgtop_sysdeps_suid-2.0 && ./a