RFR (XXL): 8038423: G1: Decommit memory within the heap

Jesper Wilhelmsson jesper.wilhelmsson at oracle.com
Wed Aug 13 15:05:46 UTC 2014

Looks good!

Thomas Schatzl skrev 12/8/14 17:12:
> Hi all,
>    can I have reviews for this change? It implements the capability for
> G1 to shrink/expand the heap on a per-region basis without the
> constraint that shrinking/expansion needs to occur at the highest
> address of the reserved space.
> Further it implements automatic commit/uncommit of all (relevant) large
> heap data structures (auxiliary data like block offset table, card
> table, mark bitmaps, hot card cache) at the same time the corresponding
> heap region is (un-)committed.
> This change implements basic support for this new behavior: selection of
> regions to (un-)commit is not particularly sophisticated.
> For easier reviewing, some notes:
> - start at the new initialization code in G1CollectedHeap::initialize()
> - all memory commit/uncommit activity of auxiliary data is tied to
> regions: the new G1RegionToSpaceMapper class manages translation between
> regions and whatever granularity the auxiliary data is
> committed/uncommitted.
> - these G1RegionToSpaceMappers are managed by HeapRegionSeq.
> This change is based on the review for JDK-8054818. As mentioned there,
> there will be some cleanup CRs after this change: at least a CR to
> rename HeapRegionSeq to HeapRegionManager, and another one that cleans
> up the card table code.
> They were split out for easier review, as they are quite large too but
> do not contribute to the functionality.
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8038423
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8038423/webrev/
> Testing:
> jprt, aurora (nightly, bigapps, lots of test suites) with -XX:+UseG1GC,
> crm fuse
> Thanks,
>    Thomas

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