After young gc (and potentially somewhere else) G1 uses the recent allocation that led to that GC to determine whether to start a concurrent mark either now or later.

However, some/most of these allocations will go into young gen, which IHOP calculation should not consider. Only known allocations into old (e.g. humongous) should be used for this calculation.

Pointed out by [~iwalulya] during review of another issue.