NP. Nailguns is per-task, but these bits of pants.ini in pants itself set a default and override for one task:

$ grep -C2 jvm_options pants.ini
[DEFAULT]
# TODO: Still needed until we migrate jvm tools to subsystems.
jvm_options: ["-Xmx1g", "-XX:MaxPermSize=256m"]

local_artifact_cache: %(pants_bootstrapdir)s/artifact_cache
--

[compile.zinc]
jvm_options: [
    '-Xmx4g', '-XX:MaxPermSize=512m', '-XX:+UseConcMarkSweepGC', '-XX:ParallelGCThreads=4',
    # bigger cache size for our big projects (default is just 5)