Garbage collect on allocation exceeding max memory pool size

[roberttoyonaga]

Summary

Garbage collection is currently done on the allocation slow path after the max eden size was already exceeded by a previous allocation. For example, if new TLAB allocationA causes the max size to be exceeded, the pool max size will remain exceeded until new TLAB allocationB happens. It would be better to do GC when the allocation that actually causes the threshold to be exceeded happens.

This is because, on the slow path, maybeCollectOnAllocation is called too early. maybeCollectOnAllocation calls shouldCollectOnAllocation which checks whether the eden size threshold is exceeded.
The problem is that maybeCollectOnAllocation is called before increaseEdenUsedBytes is called, so shouldCollectOnAllocation doesn't take into account the size of the current allocation. Is there a reason for this, or is this a bug?

I've just made a small change so that shouldCollectOnAllocation takes into account the size of the current allocation that is requiring a new TLAB (and potentially causing the memory pool max to be exceeded).

See #6930 for more context.