Acceptable memory allocation for a partition is determined during and with minimal impact on normal operation of the partitioned system. The approach includes: collecting, by a processor, statistics on a rate at which pages are transferred between uncompressed and compressed memory spaces of the partition's memory; adjusting size of the uncompressed memory space; and subsequent to the adjusting, continuing with collecting of the statistics, and referencing the resultant statistics in determining an acceptable memory allocation for the partition. In one implementation, the adjusting includes stepwise decreasing size of the uncompressed memory space by reallocating uncompressed memory space to compressed memory space, and repeating the collecting of statistics for a defined measurement period for each adjusted uncompressed memory space size until performance of the partition is negatively impacted by the reallocation of uncompressed memory space to compressed memory space.