RFR: 8234974: Shenandoah: Do concurrent roots even when no evacuation is necessary
rkennke at redhat.com
Thu Dec 12 12:08:17 UTC 2019
Sorry, I mixed up this change with the subsequent concurrent roots
cleaning here. Let's step back and get this part in shape first. Wait
for next webrev, ok?
> Second thought: I am not sure what problem you are trying to solve here,
> let's talk tomorrow.
> On 12/11/19 5:12 PM, Roman Kennke wrote:
>> After discussing off-line with Zhengyu, I am proposing those changes:
>> - Reinstate returning object for GC threads (apparently needed b/c of
>> bug in JVMTI)
>> - Always heal nmethods in barrier. We can only get there during evac
>> (see below)
>> - ShenandoahEvacUpdateOopStorageRootsClosure renamed to
>> ShenandoahEvacUpdateCleanupRootsClosure and let it also handle cleanup.
>> - Changed order of cleanup and unload: first do cleanup, then do unload.
>> - only call prepare_unloading() when we have a cset. This arms nmethods.
>> We only ever want to get into nmethod-barriers when we have a cset/are
>> doing evacuation.
>> Good now?
>>> Shenandoah can short-cut a cycle when the collection set remains empty,
>>> and doesn't dive into concurrent evacuation and updating refs phases
>>> then. However, this currently also precludes concurrent roots processing
>>> and concurrent class unloading. This is only a minor nuisance now
>>> (effectively skipping class unloading for short-cut-cycles), but amounts
>>> to a real bug when we're going to do weak-roots-cleaning concurrently
>>> Testing: hotspot_gc_shenandoah
>>> Can I please get a review?
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