why? afero change to NewMemMapFs very slowly?

[chengjia2016]

package fs

import (
"fmt"

"github.com/spf13/afero"

)

const (
OsType = "os"
Mem = "mem"
)

var supportedTypes = []string{OsType}

func GetFs(fs string) (afero.Fs, error) {
switch fs {
case OsType:
return afero.NewOsFs(), nil
case Mem:
return afero.NewMemMapFs(), nil
}
return nil, fmt.Errorf("unknown filesystem type provided: %s (supported types: %v)", fs, supportedTypes)
}