gc in golang

GC golang

Tri-color garbage collection

•

•

• garbage

Tri-color garbage collection• root scan: root ( )

push stack

• mark phase:

• stack

• stack

•

• stack ( root root )

• sweep phase heap

Tri-color garbage collection

• mark phase & sweep phase mutator pause time

Tri-color gc

• A F push stack

root scan

• stack A F push stack

mark

• B C D stack

mark

•

sweep

mark

• mark A J

write barrier

• A I

write barrier

• sweep

write barrier

write barrier

• push stack

sweep

• < current sweep > current sweep

GOGC

GOGC

• GOGC golfing GC

• GOGC=100 heap 100% GC GC = 200 200%

tradeoff• tricolor GC pause time

• heap size sweep

• throughput CPU GC

• Spatial Locality

GC example code

test codepackage main import ( "container/list" "time" ) func GenList() { l := list.New() for i := 0; i < 10000; i++ { str := "aaaaaaaaaaaaaaaaaaa" l.PushBack(str) } } func main() { count := 0 for { count++ for i := 0; i < 1000; i++ { go func() { GenList() }() } time.Sleep(500 * time.Millisecond) if count == 360 { time.Sleep(10000 * time.Millisecond) count =0 } } }

gctrace output

• CPU 32% GC

• GC pause time 0.18 + 0.98

ms

• heap size 625M

• htop 1313M

htop

slice List

test codepackage main import ( "time" ) func GenSlice() { s:= make([]string, 10000) for i:= 0;i<10000;i++ { str := "aaaaaaaaaaaaaaaaaaa" s[i] = str } } func main() { count := 0 for { count++ for i := 0; i < 1000; i++ { go func() { GenSlice() }() } time.Sleep(500 * time.Millisecond) if count == 360 { time.Sleep(10000 * time.Millisecond) count =0 } } }

gctrace output

• CPU 5% GC

• GC pause time 1.1 + 2.1 ms

• heap size 156M

Real Memory size

• htop 188M