F41 - I forgot to make a swap partition

[Robert Moskowitz]

Arg.  the Install did not default a swap partition so I forgot to work 
it in when I divided the drive as I wanted...

I am using EXT4 for my / /boot /home partitions.  Just plain 
partitioning.  Been doing it this way for lots of builds.

But this time, I missed setting aside 16Gb as a physical swap partition, 
added to the memory swap.  This system only has 16Gb memory, so the 
virtual swap starts out at 8Gb.

Since /dev/sdb4, /home is the last 800Gb with 500Gb unused, is there any 
way to safely shrink this partition 16Gb and then allocate that as swap?

thanks