[PATCH] enhancement to ParallelScavenge Full GC

[ray alex]

Hi all,

Can I have reviews for the following enhancement?

Description:
The change addresses the inefficiency in the live_words_in_range() routine
in ParallelScavenge Full GC,
which generally costs most of the time during the compacting phase.

Our idea records last query information of live_words_in_range as well as
the query result.
Our approach reuses last query result so that can reduce much computation
of bitmap searching.

Patch:  as attached.

Testing:
Manual testing of full GC intensive applications including JOlden, Dacapo,
SPECjvm2008 benchmarks.
Results show that our enhancement can reduce much full GC time by 20~50%,
depending on application scenarios.

-- 
Lei Tianyang
Institute of Parallel and Distributed System (IPADS)
Shanghai Jiao Tong University
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