[PATCH] Exploit Empty Regions in Young Gen to Enhance PS Full GC Performance

[Haoyu Li]

Hi all,

I submitted a patch about two weeks ago in the previous mail, however, I
have not received any response so far. Did I miss something? I just follow
the instructions in the webpage about *How to Contribute*. Can someone
sponsor this patch? Any reviews are well appreciated!

Best Regrads,
Haoyu Li,
Institute of Parallel and Distributed Systems(IPADS),
School of Software,
Shanghai Jiao Tong University


Haoyu Li <leihouyju at gmail.com> 于2018年12月24日周一 上午1:38写道：

> Hi all，
> I have developed a patch to enhance the full GC performance of Parallel
> Scavenge on OpenJDK 11, may I have some reviews? The patch is described as
> follows and attached in this mail.
>
> *Problem*
> Parallel Scavenge(PS) implements a compacting algorithm to do the full GC,
> and we find that this algorithm leads in terrible GC thread utilization
> (like only 8% on Derby benchmark in SPECjvm2008 suite) since there are
> serious dependencies between heap regions, i.e., a region is available to
> receive live objects from its source regions only after it has been
> collected. The work stealing does not solve this problem, idle GC threads
> cannot steal anything because most regions are unavailable to collect.
>
> *Optimization*
> We propose *shadow region* to solve the above problem. The basic idea is
> to let GC threads collect unavailable regions in advance by copying their
> live data into newly allocated empty regions, i.e., shadow regions, to
> resolve the region dependencies. The contents of shadow regions will be
> copied back to the corresponding regions later. With our approach, GC
> threads can keep working at most of the time without suffering from any
> work stealing failure (except the work stealing failure happened in the end
> of a full GC). And we notice that the to space in young gen is always
> empty, so we exploit the empty regions in to space to play the role of
> shadow regoins (if the ScavengeBeforeFullGC option is on, regions in eden
> space may be used, too) and avoid allocating shadow regions from off heap
> memory.
>
> *Evaluation*
> We evaluate the full GC performance with our patch on DaCapo, SPECjvm2008,
> JOlden benchmark suits, and the results shows that shadow region
> optimization could improve full GC throughput by 2.1X on average, up to
> 3.2X.
>
> The patch and evaluation result are attached.
>
> Best Regrads,
> Haoyu Li,
> Institute of Parallel and Distributed Systems(IPADS),
> School of Software,
> Shanghai Jiao Tong University
>
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