RFR: Exponential thread-local GCLAB sizing

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/gclabs-sizing/webrev.01/

Three changes, two preparatory:

 *) Trace and report total allocation latency and sizes
    This updates the allocation tracing report to highlight the metrics we are after.

 *) -XX:-UseTLAB should disable GCLABs too
    This allows to turn any smart thing about GCLABs off, in case there are bugs.

 *) Exponential thread-local GCLAB sizing
    This replaces the global PLABStats tracking with per-thread sizing with exponential increments,
    and quite aggressive decay. This helps to keep GCLAB sizes at bay for threads that are seldom
    using the GCLABs, and provide large enough GCLABs for threads that need it.

    We used to draw the line between mutator and GC threads in this, but it does not work all that
    great. There are Java threads that evacuate quite a lot (e.g. ~1M with current 2K GCLABs), and
    there are GC threads that evacuate almost nothing (e.g. all parallel threads that evac roots
    during final mark, but not participate in concurrent evac). New mechanics automatically adopts
    for either case. See the alloc tracing data from short SPECjbb below: we have less GCLAB allocs
    in counts, less in footprint, and have them generally larger.

I think the same could be done with TLABs, but interface there is much, much messier.

Testing: tier3_gc_shenandoah, benchmarks

Thanks,
-Aleksey


=== Before:

                             Shared   Shared GC        TLAB       GCLAB
 Counts:
                      #         500         514       52010        8078

 Latency summary:
               sum, ms:           0           0          38          10

 Sizes summary:
                sum, M:         291         113     1007348       20101

 Latency histogram (time in microseconds):
         0 -         1:         120         508       21031        6649
         1 -         2:         344           3       28752         689
         2 -         4:          31           1        1952          90
         4 -         8:           3           2         142         449
         8 -        16:           1           0          60          38
        16 -        32:           0           0           9          49
        32 -        64:           1           0          35          87
        64 -       128:           0           0          12          25
       128 -       256:           0           0          17           2

 Sizes histogram (size in bytes):
      2048 -      4096:          21           3           1        6045
      4096 -      8192:         145          60           0         216
      8192 -     16384:           3          45           0          45
     16384 -     32768:           1          51           4         481
     32768 -     65536:           2          16        2548          16
     65536 -    131072:          19         242        1728         242
    131072 -    262144:           8           0        3166           0
    262144 -    524288:          18           7        1962          23
    524288 -   1048576:          34          18        1310          18
   1048576 -   2097152:         246          64        1151          64
   2097152 -   4194304:           2           6        1217         343
   4194304 -   8388608:           0           2        1367           2
   8388608 -  16777216:           0           0        7655           0
  16777216 -  33554432:           1           0        9131           0
  33554432 -  67108864:           0           0       20770         583

=== After

                             Shared   Shared GC        TLAB       GCLAB
 Counts:
                      #         492         713       50644        3770

 Latency summary:
               sum, ms:           0           0          38           3 <--- !!!

 Sizes summary:
                sum, M:         251         113     1023531       14344 <--- !!!

 Latency histogram (time in microseconds):
         0 -         1:         166         696       19597        2808
         1 -         2:         306          14       28232         383
         2 -         4:          19           1        2539         100
         4 -         8:           1           1         125         458
         8 -        16:           0           1          76          16
        16 -        32:           0           0          10           0
        32 -        64:           0           0          41           4
        64 -       128:           0           0          14           0
       128 -       256:           0           0           9           1
       256 -       512:           0           0           1           0

 Sizes histogram (size in bytes):
      2048 -      4096:          25           0           1        1146 <--- !!!
      4096 -      8192:         221           0           2         480
      8192 -     16384:           0          97           2         483
     16384 -     32768:           1         113           6         385
     32768 -     65536:           3          28         445         338
     65536 -    131072:           1         381        1969         210
    131072 -    262144:           4           0        2766          95
    262144 -    524288:           0          16        2268          38
    524288 -   1048576:           9          26        1285          31
   1048576 -   2097152:         225          37        1080          31
   2097152 -   4194304:           2          15        1280          30
   4194304 -   8388608:           0           0        1352          29
   8388608 -  16777216:           0           0        7596          28
  16777216 -  33554432:           1           0        7477          28
  33554432 -  67108864:           0           0       23115         418