tmps does support swapping once it reaches its size limit (half of the RAM by
default but the size option changes that):
https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt
In the description:
tmpfs puts everything into the kernel internal caches and grows and
shrinks to accommodate the files it contains and is able to swap
unneeded pages out to swap space.
Interestingly, it is written later:
Some people (including me) find it very convenient to mount it e.g. on /tmp
and /var/tmp and have a big swap partition.
