runtime: combine small NoScan allocations
Combine NoScan allocations < 16 bytes into a single memory block.
Reduces number of allocations on json/garbage benchmarks by 10+%.
json-1
allocated
8039872 7949194 -1.13%
allocs 105774 93776 -11.34%
cputime
156200000 100700000 -35.53%
gc-pause-one
4908873 3814853 -22.29%
gc-pause-total
2748969 2899288 +5.47%
rss
52674560 43560960 -17.30%
sys-gc
3796976 3256304 -14.24%
sys-heap
43843584 35192832 -19.73%
sys-other
5589312 5310784 -4.98%
sys-stack 393216 393216 +0.00%
sys-total
53623088 44153136 -17.66%
time
156193436 100886714 -35.41%
virtual-mem
256548864 256540672 -0.00%
garbage-1
allocated
2996885 2932982 -2.13%
allocs 62904 55200 -12.25%
cputime
17470000 17400000 -0.40%
gc-pause-one
932757485 925806143 -0.75%
gc-pause-total
4663787 4629030 -0.75%
rss
1151074304 1133670400 -1.51%
sys-gc
66068352 65085312 -1.49%
sys-heap
1039728640 1024065536 -1.51%
sys-other
38038208 37485248 -1.45%
sys-stack
8650752 8781824 +1.52%
sys-total
1152485952 1135417920 -1.48%
time
17478088 17418005 -0.34%
virtual-mem
1343709184 1324204032 -1.45%
LGTM=iant, bradfitz
R=golang-codereviews, dave, iant, rsc, bradfitz
CC=golang-codereviews, khr
https://golang.org/cl/
38750047