![www.cloudflare.com!
Test garbage making program
func makeBuffer() []byte { !
return make([]byte, rand.Intn(5000000)+5000000) !
}!
!
func main() { !
pool := make([][]byte, 20)!
!
makes := 0 !
for { !
b := makeBuffer()
makes += 1!
!
i := rand.Intn(len(pool))!
pool[i] = b!
!
time.Sleep(time.Second)!
}!
}!](https://image.slidesharecdn.com/gomemory-130912042032-phpapp01/85/Go-memory-7-320.jpg)
![www.cloudflare.com!
Use a buffered channel
func main() {!
pool := make([][]byte, 20)!
idle:= make(chan []byte, 5)!
!
makes := 0!
for {!
var b []byte!
select {!
case b = <-idle:!
default:!
makes += 1!
b = makeBuffer()!
}!
!
!
i := rand.Intn(len(pool))!
if pool[i] != nil {!
select {!
case idle<- pool[i]:!
pool[i] = nil!
default:!
}!
}!
!
pool[i] = b!
!
time.Sleep(time.Second)!
}!
}](https://image.slidesharecdn.com/gomemory-130912042032-phpapp01/85/Go-memory-10-320.jpg)
![www.cloudflare.com!
select for non-blocking receive
idle:= make(chan []byte, 5)!
!
select {!
case b = <-idle:
!
default:!
makes += 1!
b = makeBuffer()!
}!
Try to get from the
idle queue
Idle queue
empty? Make a
new buffer
A buffered
channel makes a
simple queue](https://image.slidesharecdn.com/gomemory-130912042032-phpapp01/85/Go-memory-11-320.jpg)
![www.cloudflare.com!
select for non-blocking send
idle:= make(chan []byte, 5)!
!
select {!
case buffer <- pool[i]:!
pool[i] = nil!
!
default:!
}!
A buffered
channel makes a
simple queue
Try to return buffer
to the idle queue
Idle queue full?
GC will have to
deal with the
buffer](https://image.slidesharecdn.com/gomemory-130912042032-phpapp01/85/Go-memory-12-320.jpg)
![www.cloudflare.com!
More realistic: 20 goroutines
func main() {!
pool := make([][]byte, 200)!
!
for i := 0; i < 10; i++ {!
go func(offset int) {!
for {!
b := makeBuffer()!
j := offset+rand.Intn(20)!
pool[j] = b!
!
time.Sleep(time.Millisecond * time.Duration(rand.Intn(1000))!
}!
}(i*20)!
}!
}!](https://image.slidesharecdn.com/gomemory-130912042032-phpapp01/85/Go-memory-14-320.jpg)
![www.cloudflare.com!
Shared across goroutines
func main() {!
buffer := make(chan []byte, 5)!
!
pool := make([][]byte, 200)!
for i := 0; i < 10; i++ {!
go func(offset int) {!
for {!
var b []byte!
select {!
case b = <-buffer:!
default: b = makeBuffer()!
}!
j := offset+rand.Intn(20)!
if pool[j] != nil {!
select {!
case buffer <- pool[j]: pool[j] = nil!
default:!
}!
}!
pool[j] = b!
time.Sleep(time.Millisecond * time.Duration(rand.Intn(1000))!
}!
}(i*20)!
}!
!](https://image.slidesharecdn.com/gomemory-130912042032-phpapp01/85/Go-memory-16-320.jpg)
![www.cloudflare.com!
Also
• This works for things other than []byte
• Can be done with arbitrary types
• Just need some way to reset
• There’s a proposal to add something like this to the Go
package library
• sync.Cache
• Follow TODO](https://image.slidesharecdn.com/gomemory-130912042032-phpapp01/85/Go-memory-22-320.jpg)
Go memory
- 1. www.cloudflare.com! Understanding Go Memory September 11, 2013 John Graham-Cumming
- 2. www.cloudflare.com! Allocation Primitives • new(T)! • Allocates memory for item with type T! • Zeroes it ! • make(T)! • Allocates memory for item with type T! • Initializes it • Needed for channels, maps and slices • Memory comes from internal heap ret = runtime·mallocgc(typ->size, flag, 1, 1);! zeroed
- 3. www.cloudflare.com! Two memory freeing processes • Garbage collection • Determines which blocks of memory are no longer used • Marks areas of heap so they can be reused by your program • Scavenging • Determines when parts of the heap are idle for a long time • Returns memory to the operation system
- 4. www.cloudflare.com! Garbage collection • Controlled by the GOGC environment variable • And by debug.SetGCPercentage()! • Default is same as GOGC=100! • Can set GOGC=off or debug.SetGCPercentage(-1) (no garbage collection at all) // Initialized from $GOGC. GOGC=off means no gc.! //! // Next gc is after we've allocated an extra amount of! // memory proportional to the amount already in use.! // If gcpercent=100 and we're using 4M, we'll gc again! // when we get to 8M. This keeps the gc cost in linear! // proportion to the allocation cost. Adjusting gcpercent! // just changes the linear constant (and also the amount of! // extra memory used).!
- 5. www.cloudflare.com! Scavenging • Runs once per minute • Can also force return of all unused memory by calling debug.FreeOSMemory()! // If we go two minutes without a garbage collection, ! // force one to run.! forcegc = 2*60*1e9;! ! // If a span goes unused for 5 minutes after a garbage! // collection, we hand it back to the operating system.! limit = 5*60*1e9;!
- 6. www.cloudflare.com! Memory Statistics • Read with runtime.ReadMemStats(&m) ! • The MemStats struct has tons of members • Useful ones for looking at heap • HeapInuse - # bytes in the heap allocated to things • HeapIdle - # bytes in heap waiting to be used • HeapSys - # bytes obtained from OS • HeapReleased - # bytes released to OS
- 7. www.cloudflare.com! Test garbage making program func makeBuffer() []byte { ! return make([]byte, rand.Intn(5000000)+5000000) ! }! ! func main() { ! pool := make([][]byte, 20)! ! makes := 0 ! for { ! b := makeBuffer() makes += 1! ! i := rand.Intn(len(pool))! pool[i] = b! ! time.Sleep(time.Second)! }! }!
- 10. www.cloudflare.com! Use a buffered channel func main() {! pool := make([][]byte, 20)! idle:= make(chan []byte, 5)! ! makes := 0! for {! var b []byte! select {! case b = <-idle:! default:! makes += 1! b = makeBuffer()! }! ! ! i := rand.Intn(len(pool))! if pool[i] != nil {! select {! case idle<- pool[i]:! pool[i] = nil! default:! }! }! ! pool[i] = b! ! time.Sleep(time.Second)! }! }
- 11. www.cloudflare.com! select for non-blocking receive idle:= make(chan []byte, 5)! ! select {! case b = <-idle: ! default:! makes += 1! b = makeBuffer()! }! Try to get from the idle queue Idle queue empty? Make a new buffer A buffered channel makes a simple queue
- 12. www.cloudflare.com! select for non-blocking send idle:= make(chan []byte, 5)! ! select {! case buffer <- pool[i]:! pool[i] = nil! ! default:! }! A buffered channel makes a simple queue Try to return buffer to the idle queue Idle queue full? GC will have to deal with the buffer
- 14. www.cloudflare.com! More realistic: 20 goroutines func main() {! pool := make([][]byte, 200)! ! for i := 0; i < 10; i++ {! go func(offset int) {! for {! b := makeBuffer()! j := offset+rand.Intn(20)! pool[j] = b! ! time.Sleep(time.Millisecond * time.Duration(rand.Intn(1000))! }! }(i*20)! }! }!
- 16. www.cloudflare.com! Shared across goroutines func main() {! buffer := make(chan []byte, 5)! ! pool := make([][]byte, 200)! for i := 0; i < 10; i++ {! go func(offset int) {! for {! var b []byte! select {! case b = <-buffer:! default: b = makeBuffer()! }! j := offset+rand.Intn(20)! if pool[j] != nil {! select {! case buffer <- pool[j]: pool[j] = nil! default:! }! }! pool[j] = b! time.Sleep(time.Millisecond * time.Duration(rand.Intn(1000))! }! }(i*20)! }! !
- 18. www.cloudflare.com! More realistic example • Alter code to • Always try to give back a random buffer from the pool • 50% of the time get a new one • Should create more garbage
- 22. www.cloudflare.com! Also • This works for things other than []byte • Can be done with arbitrary types • Just need some way to reset • There’s a proposal to add something like this to the Go package library • sync.Cache • Follow TODO