RFR: Aggregated bitmap slicing

[Roman Kennke]

Am 11.10.2017 um 17:05 schrieb Aleksey Shipilev:
> http://cr.openjdk.java.net/~shade/shenandoah/bitmaps-uncommit-aggr/wevrev.01/
>
> Bitmap slice uncommit works well on x86, where the default page size is 4K. But, on platforms that
> have larger default page sizes, notably AArch64 that has 64K pages, current bitmap slicing drives
> the minimum region size to at least 4M, and 10 min regions take 40M of Java heap. This is not
> pleasant, and we can do better.
>
> The way out is to aggregate regions per each bitmap slice: when all regions with the bitmap slice
> uncommit, uncommit the bitmap slice. When at least one region is committed, commit the entire slice.
> This works well for compact idle heaps.
>
> On the plus side, this also works with UseLargePages for bitmaps!
>
> Testing: hotspot_gc_shenandoah
>
> Thanks,
> -Aleksey
>
Good!