RFR: Trim the TLAB sizes to avoid wasteful retirement under TLAB races

[Aleksey Shipilev]

On 09/20/2017 09:17 PM, Aleksey Shipilev wrote:
> http://cr.openjdk.java.net/~shade/shenandoah/tlab-race-trim/webrev.01/
> 
> This implements TLAB trimming to avoid wasteful retirement. The rationale is given in the comment
> right in the code. It does not seem to make allocation significantly more costly. To make it less
> overheady, changed the counter update code to be called on new region issuance, not on TLAB issuance.

Added more discussion:
  http://cr.openjdk.java.net/~shade/shenandoah/tlab-race-trim/webrev.02/

-Aleksey