@Override
                public void getConfig(ProtonConfig.Builder builder) {
                    if (search != null) {
                        if (search.equals(IoType.POPULATE)) {
                            builder.search.mmap.options.add(ProtonConfig.Search.Mmap.Options.POPULATE);
                        }
                    }
                }
Class representing the tuning config used for a search cluster.
Take a look at proton.def and vespa doc for detailed explanations.

@author geirst
config-model/src/main/java/com/yahoo/vespa/model/search/Tuning.java