The document discusses tri-color garbage collection used in Go. It has three main phases: root scanning to identify reachable objects, mark phase to mark reachable objects, and sweep phase to free unmarked objects. This approach aims to minimize mutator pause times during garbage collection by using a write barrier to track pointers to unscanned objects during concurrent marking. The document also provides examples comparing memory usage and GC performance between using lists versus slices in Go code.

1. GC
golang

2. Tri-color garbage collection
•
•
• garbage

3. Tri-color garbage collection
• root scan: root ( )
push stack
• mark phase:
• stack
• stack
•
• stack (
root root )
• sweep phase heap

4. Tri-color garbage collection
• mark phase & sweep phase
mutator pause time

5. Tri-color gc

7. • A F push stack
root scan

8. • stack A F push stack
mark

9. • B C D stack
mark

10. •
sweep

11. mark

12. • mark A J
write barrier

13. • A I
write barrier

14. • sweep
write barrier

15. write barrier
• push stack

16. sweep

17. • < current sweep > current sweep

18. GOGC

19. GOGC
• GOGC golfing GC
• GOGC=100 heap 100%
GC GC = 200 200%

21. tradeoff
• tricolor GC pause time
• heap size
sweep
• throughput CPU
GC
• Spatial
Locality

22. GC
example code

23. test code
package 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
}
}
}

24. gctrace output
• CPU 32%
GC
• GC pause time
0.18 + 0.98
ms
• heap size
625M

25. • htop 1313M
htop

26.
slice List

27. test code
package 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
}
}
}

28. gctrace output
• CPU 5%
GC
• GC pause time
1.1 + 2.1 ms
• heap size
156M

29. Real Memory size
• htop 188M