/etc/default/tmpfs, tmpfs for /tmp etc. Howto in systemd?

[U.Mutlu]

Martin Pitt wrote on 03/31/2019 07:01 PM:
> U.Mutlu [2019-03-30 22:08 +0100]:
>> But, I don't know where the other tmpfs-mounts below are defined.
>> tmpfs           501M     0  501M   0% /dev/shm
>> tmpfs           501M   14M  487M   3% /run
>> tmpfs           5.0M     0  5.0M   0% /run/lock
>> tmpfs           501M     0  501M   0% /sys/fs/cgroup
>
> These are mounted by systemd by default during early boot. They need to be
> always present on a system, so there's no point configuring them.

Hi thx,
what about their sizes? How are they determined/calculated, and defined where?
Can admin set own values?