I pinged backstage and here is the recommendation:
DB2_OVERRIDE_BPF
Operating system: All
Default: not set, Values: a positive numeric number of pages OR
<entry>[;<entry>…] where <entry>=<buffer pool ID>,<number of pages>
This variable specifies the size of the buffer pool, in pages, to be
created at database activation, rollforward recovery, or crash recovery.
It is useful when memory constraints cause failures to occur during
database activation, rollforward recovery, or crash recovery. The memory
constraint could arise either in the rare case of a real memory shortage
or, because of the attempt by the database manager to allocate a large
buffer pool, in the case where there were inaccurately configured buffer
pools. For example, when even a minimal buffer pool of 16 pages is not
brought up by the database manager, try specifying a smaller number of
pages using this environment variable. The value given to this variable
overrides the current buffer pool size.
You can also use <entry>[;<entry>…] where <entry>=<buffer pool
ID>,<number of pages> to temporarily change the size of all or a subset
of the buffer pools so that they can start up.