RFR: Mark-compact performance improvements and cleanups

[Aleksey Shipilev]

On 05/29/2018 09:20 PM, Aleksey Shipilev wrote:
> http://cr.openjdk.java.net/~shade/shenandoah/mark-compact-improvs/webrev.01/
> 
> This is the pack of mark-compact cleanups and improvements.
> 
> *) mc-logging: More verbose profiling for phase 4 in mark-compact
> 
> Adds a few more profiling points in "Copy object" phase of mark compact, which enables better
> performance diagnostics.
> 
> *) mc-liveness: Full GC always comes with liveness data
> 
> We used to skip liveness counting for mark-compact, because the core algorithm does not require it.
> It provided some boosts when our liveness calculation was a major performance hog. It is not
> anymore, and having liveness data enables us to do shortcuts, like below. This also cleans up shared
> code substantially.
> 
> *) mc-immediate-trash: Reclaim immediate garbage after mark-compact marking
> 
> Once we know liveness, we can reclaim immediate garbage regions right after marking. This lets
> threads down below treat the regions as the targets for compaction immediately, instead of
> compacting through them. This is especially important for figuring out compaction for humongous
> regions, which is planned before the regular object moves.
> 
> *) mc-shortcut-live: Shortcut regions that are known not to be alive
> 
> Same here, liveness provides us with insight if we even want to walk marked objects in the region,
> or not. For the fully-garbage region it would be futile, and it will yield no marked objects.

A few more touchups and code moves here:
  http://cr.openjdk.java.net/~shade/shenandoah/mark-compact-improvs/webrev.02/

*) mc-recycle-once: Recycle the regions only once

There is no need to recycle before the mark, if we are recycling after mark anyway.

*) mc-prepare-mark-closure: Rename and move ShenandoahPrepareForMarkClosure

Renames and moves the closure to its only use.

Testing: hotspot_gc_shenandoah, benchmarks

Thanks,
-Aleksey