RFR: Use PLAB for evacuations instead of TLAB

[Aleksey Shipilev]

On 05/11/2018 11:25 PM, Roman Kennke wrote:
> Full:
> http://cr.openjdk.java.net/~rkennke/plab-gclab/webrev.05/

Looks OK. I have a few final questions:

 *) On this path we can fire assert with -UseTLAB?

 256 inline HeapWord* ShenandoahHeap::allocate_from_gclab(Thread* thread, size_t size) {
 257   PLAB* gclab = ShenandoahThreadLocalData::gclab(thread);
 258   if (gclab == NULL) {
 259     assert(!thread->is_Java_thread() && !thread->is_Worker_thread(),
 260            "Performance: thread should have GCLAB: %s", thread->name());
 261     // No GCLABs in this thread, fallback to shared allocation
 262     return NULL;
 263   }

Otherwise OK.

-Aleksey