The textproc/elasticsearch5 port installs configuration files
into /usr/local/etc/elasticsearch/, but the jvm.options there
is ignored, JVM options cannot be configured as documented.

The /usr/local/lib/elasticsearch/bin/elasticsearch shell script
contains the following code section:

if [ -z "$ES_JVM_OPTIONS" ]; then
    for jvm_options in "$ES_HOME"/config/jvm.options \
                      /etc/elasticsearch/jvm.options; do
        if [ -r "$jvm_options" ]; then
            ES_JVM_OPTIONS=$jvm_options
            break
        fi
    done
fi

... which is looking for a file jvm.options in /etc/elasticsearch/,
yet this options file is actually installed by the package
in the directory /usr/local/etc/elasticsearch/ and is therefore
being ignored.