[11u] RFR (XS) 8261251: Shenandoah: Use object size for full GC humongous compaction

[Aleksey Shipilev]

Original bug:
   https://bugs.openjdk.java.net/browse/JDK-8261251
   https://git.openjdk.java.net/jdk/commit/deb0544f

The patch does not apply cleanly to 11u, because of the shenandoahMarkCompact -> shenandoahFullGC 
rename. I applied the same patch to the new file without problems.

11u variant:

diff -r a4e1ec47729f src/hotspot/share/gc/shenandoah/shenandoahMarkCompact.cpp
--- a/src/hotspot/share/gc/shenandoah/shenandoahMarkCompact.cpp Thu Jan 28 09:50:21 2021 +0000
+++ b/src/hotspot/share/gc/shenandoah/shenandoahMarkCompact.cpp Mon Feb 15 10:50:03 2021 +0100
@@ -905,7 +905,7 @@

        Copy::aligned_conjoint_words(heap->get_region(old_start)->bottom(),
                                     heap->get_region(new_start)->bottom(),
-                                   ShenandoahHeapRegion::region_size_words()*num_regions);
+                                   words_size);

        oop new_obj = oop(heap->get_region(new_start)->bottom());
        new_obj->init_mark_raw();

Testing: hotspot_gc_shenandoah; tier{1,2} with Shenandoah

-- 
Thanks,
-Aleksey