G1 mixed gc by default sizes the young gen to the minimum allowed as default GCPauseIntervalMillis is MaxGCPauseMillis.

This causes unnecessary heap expansions as the actual gc time ratio will spike at that time, particularly at the end of mixed gc although there is enough space left.

One potential fix is to make sure that GCPauseTimeRatio and the ratio between MaxGCPauseMillis/GCPauseIntervalMillis is kept in sync.