RFR: Remove matrix operations from concurrent mark

[Roman Kennke]

Am 30.05.2017 um 20:33 schrieb Aleksey Shipilev:
> We have discussed this before: matrix is needed for partial collections, partial
> collections force update-refs phase, and update-refs rebuilds the matrix.
> Therefore, matrix rebuild is not needed during concurrent mark. Moreover, we now
> do double work: we first rebuild matrix during concmark, and then do it again
> during update-refs! This is excessive.
>
> This removes matrix operations from concurrent mark:
>   http://cr.openjdk.java.net/~shade/shenandoah/matrix-remove-cm/webrev.01/
>
> Testing: hotspot_gc_shenandoah
>
> Thanks,
> -Aleksey
>
Very good, yes!

Roman