gc debug problem

[sandao]

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?    go version is 1.12.7.

[fge...@gmail.com]

when as is allocated on the stack, gc has a smaller task.

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[sandao]

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：

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[fge...@gmail.com]

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)

[sandao]

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：