Question about 'anonymous' UMA zones

[Karsten König]

Hello y'all,

I'm sorry for cross-posting but after second examination this list feels
more appropriate for my question.

I just played a little bit with the zone allocator of the FreeBSD kernel
and observed the following: All 'anonymous' zones (is this the
appropriate term?) with a size smaller than 512 Bytes have no slabs in
my 11.1-VM. This is not the case on my bare metal server (11.1, too).
This is the output:

# vmstat -z
ITEM                   SIZE  LIMIT     USED     FREE      REQ FAIL SLEEP
...
16:                      16,      0,       0,       0,       0,   0,   0

32:                      32,      0,       0,       0,       0,   0,   0

64:                      64,      0,       0,       0,       0,   0,   0

128:                    128,      0,       0,       0,       0,   0,   0

256:                    256,      0,       0,       0,       0,   0,   0

512:                    512,      0,    7906,      70,   97681,   0,   0
...

I would like to know why this is the case; can someone explain this to
me? What happens if I allocate e.g. a 256 Byte buffer?

Best,

Karsten