RFR: Evac reserve: make sure GC has untouchable space to move the objects into

[Aleksey Shipilev]

On 08/30/2018 07:38 PM, Roman Kennke wrote:
> Seems reasonable.
> 
> -XX:ShenandoahEvacReserve=0 turns it off? Then maybe use range(0, 100)?

This feature is cannot be disabled. It seemed simpler than doubling all the paths for with- and
without-evac-reserve. ShenandoahEvacReserve=0 basically means "no space for evacs, ever", which
screws the GC, therefore the lower bound is not zero.

> Also, the ranges in shenandoah_globals.hpp (1,100) seem strange for a
> double.

1.0 is the proper lower bound for ShenandoahEvacReserveWaste, because waste < 1 means we cut out the
cset *larger* than the evac reserve, which again screws the GC.

Thanks,
-Aleksey