Why don't roaringBitmap aggregation functions need to use Arena?

[f0rest9999]

In the documentation https://github.com/ClickHouse/ClickHouse/blob/master/docs/en/development/architecture.md, The "States are allocated in Arena (a memory pool) to deal with multiple states while executing a high-cardinality GROUP BY query. " was mentioned.

But I found RoaringBitmap aggregation function not use arena to allocate memory to store the states.
cpp: src/AggregateFunctions/AggregateFunctionGroupBitmap.cpp
bool allocatesMemoryInArena() const override { return false; }.

It is possible that the RoaringBitmap is too large and exceeds the limit. And this seems to fit what markdown wrote above.
So I am confused that how does ClickHouse allocate memory and keep track of memory during the execution of RoaringBitmap aggregation. Is there a memory tracker with a hidden mechanism?