Goroutine Stack Size Evolve

原文链接

Go provides a light and smart goroutines management. Light because the goroutine stack starts at 2Kb only, and smart since goroutines can grow / shrink automatically according to our needs.

Regarding the size of the stack, we can find it in runtime/stack.go :

1 2	// The minimum size of stack used by Go code _StackMin = 2048

func main() {
   a := 1
   b := 2

   r := max(a, b)
   println(`max: `+strconv.Itoa(r))
}

func max(a int, b int) int {
   if a >= b {
      return a
   }

   return b
}

go build -gcflags -S main.go

"".main STEXT size=186 args=0x0 locals=0x70
   0x0000 00000 (/go/src/main.go:5)    TEXT   "".main(SB), ABIInternal, $112-0
   [...]
   0x00b0 00176 (/go/src/main.go:5) CALL   runtime.morestack_noctxt(SB)
[...]
0x0000 00000 (/go/src/main.go:13)    TEXT   "".max(SB), NOSPLIT|ABIInternal, $0-24

There are two instructions that involves the stack changes:

CALL runtime.morestack_noctxt: this method will increase the size of the stack if it needs more.
NOSPLIT: this instruction means that the stack overflow check is not needed. It is similar to the compiler directive //go:nosplit.

runtime: newstack sp=0xc00002e6d8 stack=[0xc00002e000, 0xc00002e800]
copystack gp=0xc000000300 [0xc00002e000 0xc00002e6e0 0xc00002e800] -> [0xc000076000 0xc000076ee0 0xc000077000]/4096
stackfree 0xc00002e000 2048
stack grow done
runtime: newstack sp=0xc000076888 stack=[0xc000076000, 0xc000077000]
copystack gp=0xc000000300 [0xc000076000 0xc000076890 0xc000077000] -> [0xc00003e000 0xc00003f890 0xc000040000]/8192
stackfree 0xc000076000 4096
stack grow done

The strategy to copy the stack into a bigger space is called contiguous stack as opposed to segmented stack

类似于普通操作系统的segment stacks管理？

rust部分，不采用这种方式，

stack thrashing的问题，需要事先分配
FFI，外部code往往都需要large stacks
LLVM libc optimizations and intrinsic fallbacks

Instead of segmented stacks we’re going to rely on the OS and MMU to help us map pages lazily