Innodb buffer can fill up on things like during a mariadb-dump.
The logically successor to MDEV-25340 to keep only the memory required for innodb actually mapped is as part of the LRU to purge off old pages if they really haven't been used in a while. These will be still allocated to mariadbd, however in a virtual non-paged in sense.
This can be done on linux with madvise(MADV_FREE) (Linux and FreeBSD). Windows has VirtualFree MEM_DECOMMIT/MEM_RESET.
These a proactive releases, and them mechanisms implemented can be reused to serve reactive mechanism like MDEV-24670.