## What changes were proposed in this pull request?
Before this change, we would always allocate 64MB per aggregation task for the first-level hash map storage, even when running in low-memory situations such as local mode. This changes it to use the memory manager default page size, which is automatically reduced from 64MB in these situations.
cc ooq JoshRosen
## How was this patch tested?
Tested manually with `bin/spark-shell --master=local[32]` and verifying that `(1 to math.pow(10, 3).toInt).toDF("n").withColumn("m", 'n % 2).groupBy('m).agg(sum('n)).show` does not crash.
Author: Eric Liang <ekl@databricks.com>
Closes#15016 from ericl/sc-4483.
722afbb2b3