RFR: -Xlog:gc+ergo and heuristics UX fixes (pack of three)

[Roman Kennke]

That's cool. Good to go!

Roman


> http://cr.openjdk.java.net/~shade/shenandoah/gc-ergo-ux/webrev.01/
> 
> This does three UX changes that turns gc+ergo and heuristics less noisy and more correct:
> 
> The pack includes:
> 
>  *) adaptive-cset: UX: Cleanup (adaptive) CSet selection message
>       This unclutters the message, and aligns it better format-wise.
> 
>  *) shorter-ergo:  UX: Shorter gc+ergo messages from CSet selection
>       Ditches some noisy lines that we don't really care about, and cleans up
>       related code. Computes total garbage on the fly, without involving another
>       walk over the regions, also skips CSet selection if we know we do not needed
>       due to immediate garbage. This gives a marginal performance boost.
> 
>  *) pacer-tax:     UX: Pacer reports incorrect free size
>       Fixes Pacer to report correct "free". Currently it reports free after subtracting
>       non-taxable base, which is confusing.
> 
> Testing: hotspot_gc_shenandoah
> 
> --- Before:
> 
>  Adaptive CSet selection: free target = 35840M, actual free = 27968M; min cset = 7872M, max cset =
> 20976M
>  Total Garbage: 55264M
>  Immediate Garbage: 0M, 0 regions (0% of total)
>  Garbage to be collected: 53777M (97% of total), 1927 regions
>  Live objects to be evacuated: 7862M
>  Live/garbage ratio in collected regions: 14%
>  Free: 27968M, 874 regions (27% of total)
>  Pacer for Evacuation. CSet: 7862M, Free: 25149M, Non-Taxable: 2794M, Alloc Tax Rate: 1.1x
> 
> --- After (with collectable garbage):
> 
>  Adaptive CSet Selection. Target Free: 35840M, Actual Free: 27904M, Target CSet: [7936M, 20928M]
>  Collectable Garbage: 53824M (97% of total), 7927M CSet, 1930 CSet regions
>  Immediate Garbage: 0M (0% of total), 0 regions
>  Free: 27904M, 872 regions
>  Pacer for Evacuation. CSet: 7927M, Free: 27904M, Non-Taxable: 2790M, Alloc Tax Rate: 1.1x
> 
> --- After (with only immediate garbage):
> 
>  Immediate Garbage: 11430M (99% of total), 2858 regions
>  Free: 4908M, 1227 regions
>  Pacer for Evacuation. CSet: 0M, Free: 4912M, Non-Taxable: 491M, Alloc Tax Rate: 1.1x
> 
> 
> Thanks,
> -Aleksey
>