-Xmn

Sets the initial and maximum size of the new area to the specified value when using -Xgcpolicy:gencon.

-Xmn<size>
Equivalent to setting both -Xmns and -Xmnx. If you set either -Xmns or -Xmnx, you cannot set -Xmn. If you try to set -Xmn with either -Xmns or -Xmnx, the VM does not start, returning an error. By default, -Xmn is not set. If the scavenger is disabled, this option is ignored.