RFR: Aggregated bitmap slicing

[Zhengyu Gu]

Good to me.

-Zhengyu

On 10/11/2017 11:19 AM, Roman Kennke wrote:
> 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!
>