escapes to heap,use "go tool compile -m".
在 2019年8月15日星期四 UTC+8下午12:06:20，Gergely Födémesi写道：
>
>
>
> On Thu, Aug 15, 2019, 05:19 sandao <yiren...@gmail.com <javascript:>>
> wrote:
>
>> In my opinion, the slice which "as" point to, is all allocated on the
>> heap in two case . so, I think the mark time should not be so different.
>> Can you tell me more details for you answer(when as is allocated on the
>> stack, gc has a smaller task.)?
>>
>> 在 2019年8月15日星期四 UTC+8上午11:02:46，Gergely Födémesi写道：
>>>
>>> .On Wed, Aug 14, 2019, 17:56 sandao <yiren...@gmail.com> wrote:
>>>
>>>> type A struct {
>>>> a int
>>>> }
>>>>
>>>> func gen() []*A {
>>>> r := make([]*A, 1000000)
>>>> for i := 0; i < len(r); i++ {
>>>> r[i] = &A{i}
>>>> }
>>>> return r
>>>> }
>>>>
>>>> //var as []*A = gen()
>>>>
>>>> func main() {
>>>> go func() {
>>>> err := http.ListenAndServe(":8034", nil)
>>>> if err != nil {
>>>> //fmt.Printf("ListenAndServe:%s\n", err)
>>>> }
>>>> }()
>>>> var as []*A = gen()
>>>> fmt.Println(as[0])
>>>> time.Sleep(100 * time.Second)
>>>> }
>>>>
>>>> when debug gc:
>>>> 1) if the "var as []*A = gen()" is in main , the debug info is
>>>> : gc 4 @2.757s 0%: 0.049+0.59+0.025 ms clock, 2.3+0/0.54/0.28+1.2 ms
>>>> cpu, 16->16->0 MB, 31 MB goal, 48 P (forced)
>>>> 2) if the "var as []*A = gen()" is not in main, the debug info
>>>> is: gc 9 @7.172s 0%: 0.077+25+0.020 ms clock, 3.7+0/24/0.73+0.99 ms
>>>> cpu, 16->16->15 MB, 31 MB goal, 48 P (forced)
>>>>
>>>> Anybody konw why the mark time (red numbers) is so different?
>>>>
>>>
>>> when as is allocated on the stack, gc has a smaller task.
>>>
>>
> see for yourself what the compiler says about that decision:
> https://golang.org/cmd/compile/
> you'll need -m
>
> you can also use pprof to check your assumptions.
>
> (there isn't any computer near me currently)
>
>
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