Can free swap size be determined from the sysctl information ?

It seems that it should be possible to find free swap size from the 
sysctl information, but it isn't obvious how to do this.


Here are all *swap* entries in the sysctl information:
$ sysctl -a | grep swap
0 MD md98 68719441408 512 u 98 s 512 f 0 fs 0 l 68719441408 t vnode file 
/disk-large1/swap-64GB label
z0xfffff8004d862400 [shape=box,label="SWAP\nswap\nr#2"];
      <name>swap</name>
            <file>/disk-large1/swap-64GB</file>
vm.swap_enabled: 1
vm.domain.0.stats.unswappable: 0
vm.swap_idle_threshold2: 10
vm.swap_idle_threshold1: 2
vm.swap_idle_enabled: 0
vm.disable_swapspace_pageouts: 0
vm.stats.vm.v_swappgsout: 433264
vm.stats.vm.v_swappgsin: 94457
vm.stats.vm.v_swapout: 65078
vm.stats.vm.v_swapin: 11121
vm.stats.swap.free_completed: 65205
vm.stats.swap.free_deferred: 86103
vm.nswapdev: 1
vm.swap_fragmentation:
vm.swap_async_max: 4
vm.swap_maxpages: 48890752
vm.swap_total: 68719439872
vm.swap_reserved: 16267402461184


top(1) shows 775M of free swap out of 64G total.
top(1) gets swap information from kvm_getswapinfo(3).


Motivation: one Golang-based port needs free swap size information, and 
I am trying to figure out how to get this information in Golang.

Golang has the "sysctl" module.



Thanks,

Yuri