Comment # 1 on bug 1204380 from Vlastimil Babka

Was there a previous Leap 15.4 kernel version where you could say this wasn't
happening?

It looks like shmem memory leak without visible users.

I'd recommend booting with page_owner=on, if you can tolerate some associated
memory/cpu overhead. Once Shmem becomes prominent enough (can be before swap
starts to be used), try capturing the largest memory users with the help of
tools/vm/page_owner_sort.c (details in Documentation/mm/page_owner.rst ) and
hopefully that will tell us something.