Uncommit delay option

[Aleksey Shipilev]

On 10/12/19 3:33 PM, Holger Hoffstätte wrote:
> The option is called ShenandoahUncommitDelay (in milliseconds), e.g.
> -XX:ShenandoahUncommitDelay=60000 will try to uncommit every minute.
> Note that this doesn't *guarantee* RSS shrinking on every interval;
> it might take a concurrent cycle or two for regions to be compact
> enough.

To add to this, ShenandoahUncommitDelay means the time the empty region stays committed. What is
important here is that regions become empty as GC acts on the heap, which means whatever small
uncommit delay would be useless unless you have GC cycles running as well.

When optimizing for footprint, I would start with "compact" heuristics that tunes down everything to
the densest extreme, and then worked backwards opting out of some of the tuning it ergonomically
applied, checking it does not regress footprint numbers for your scenario. GC logs should say at the
start what adjustments the heuristics made.

Stefan, be sure to read our wiki page:
  https://wiki.openjdk.java.net/display/Shenandoah

-- 
Thanks,
-Aleksey