memstat HeapInuse and TotalAlloc need explain-CodePudding

i want dump golang memstat

package main

import (
    "fmt"
    "github.com/dustin/go-humanize"
    "runtime"
    "time"
)

func main() {
    for {
        var mem = new(runtime.MemStats)
        runtime.ReadMemStats(mem)
        fmt.Println("HeapInuse:", humanize.Bytes(mem.HeapInuse), "TotalAlloc:", humanize.Bytes(mem.TotalAlloc))

        allocate()
        time.Sleep(100 * time.Millisecond)
    }

}

func allocate() {
    //  0.25MB
    _ = make([]byte, int((1<<20)*0.25))
}

when i dump the mem info

HeapInuse: 418 kB TotalAlloc: 154 kB ? why  HeapInuse bigger than TotalAlloc
HeapInuse: 688 kB TotalAlloc: 417 kB
HeapInuse: 950 kB TotalAlloc: 680 kB
HeapInuse: 1.2 MB TotalAlloc: 942 kB
HeapInuse: 1.5 MB TotalAlloc: 1.2 MB
HeapInuse: 1.8 MB TotalAlloc: 1.5 MB
HeapInuse: 2.0 MB TotalAlloc: 1.7 MB
HeapInuse: 2.3 MB TotalAlloc: 2.0 MB
HeapInuse: 2.5 MB TotalAlloc: 2.3 MB
HeapInuse: 2.8 MB TotalAlloc: 2.5 MB
HeapInuse: 3.1 MB TotalAlloc: 2.8 MB
HeapInuse: 3.3 MB TotalAlloc: 3.0 MB
HeapInuse: 3.6 MB TotalAlloc: 3.3 MB
HeapInuse: 3.9 MB TotalAlloc: 3.6 MB
HeapInuse: 4.1 MB TotalAlloc: 3.8 MB
HeapInuse: 4.4 MB TotalAlloc: 4.1 MB
HeapInuse: 410 kB TotalAlloc: 4.4 MB

i found HeapInuse bigger than TotalAlloc? but i cannt understand reason ? i think the totalAlloc should include HeapInuse.

CodePudding user response：

Let's read the official comments below:

TotalAlloc

// TotalAlloc is cumulative bytes allocated for heap objects.
//
// TotalAlloc increases as heap objects are allocated, but
// unlike Alloc and HeapAlloc, it does not decrease when
// objects are freed.
TotalAlloc uint64

HeapInuse

// HeapInuse is bytes in in-use spans.
//
// In-use spans have at least one object in them. These spans
// can only be used for other objects of roughly the same
// size.
//
// HeapInuse minus HeapAlloc estimates the amount of memory
// that has been dedicated to particular size classes, but is
// not currently being used. This is an upper bound on
// fragmentation, but in general this memory can be reused
// efficiently.
HeapInuse uint64

HeapInuse is memory allocated (from the OS), may not be used by objects
TotalAlloc is memory allocated for heap objects

Let's try HeapAlloc

// HeapAlloc is bytes of allocated heap objects.
//
// "Allocated" heap objects include all reachable objects, as
// well as unreachable objects that the garbage collector has
// not yet freed. Specifically, HeapAlloc increases as heap
// objects are allocated and decreases as the heap is swept
// and unreachable objects are freed. Sweeping occurs
// incrementally between GC cycles, so these two processes
// occur simultaneously, and as a result HeapAlloc tends to
// change smoothly (in contrast with the sawtooth that is
// typical of stop-the-world garbage collectors).
HeapAlloc uint64

Result

HeapAlloc: 148 kB HeapInuse: 401 kB TotalAlloc: 148 kB
HeapAlloc: 412 kB HeapInuse: 664 kB TotalAlloc: 412 kB
HeapAlloc: 675 kB HeapInuse: 926 kB TotalAlloc: 675 kB
HeapAlloc: 937 kB HeapInuse: 1.2 MB TotalAlloc: 937 kB
HeapAlloc: 1.2 MB HeapInuse: 1.5 MB TotalAlloc: 1.2 MB
HeapAlloc: 1.5 MB HeapInuse: 1.7 MB TotalAlloc: 1.5 MB
HeapAlloc: 1.7 MB HeapInuse: 2.0 MB TotalAlloc: 1.7 MB
HeapAlloc: 2.0 MB HeapInuse: 2.2 MB TotalAlloc: 2.0 MB
HeapAlloc: 2.2 MB HeapInuse: 2.5 MB TotalAlloc: 2.2 MB
HeapAlloc: 2.5 MB HeapInuse: 2.8 MB TotalAlloc: 2.5 MB
HeapAlloc: 2.8 MB HeapInuse: 3.0 MB TotalAlloc: 2.8 MB
HeapAlloc: 3.0 MB HeapInuse: 3.3 MB TotalAlloc: 3.0 MB
HeapAlloc: 3.3 MB HeapInuse: 3.6 MB TotalAlloc: 3.3 MB
HeapAlloc: 3.6 MB HeapInuse: 3.8 MB TotalAlloc: 3.6 MB
HeapAlloc: 3.8 MB HeapInuse: 4.1 MB TotalAlloc: 3.8 MB
HeapAlloc: 4.1 MB HeapInuse: 4.3 MB TotalAlloc: 4.1 MB
HeapAlloc: 134 kB HeapInuse: 393 kB TotalAlloc: 4.4 MB
HeapAlloc: 398 kB HeapInuse: 664 kB TotalAlloc: 4.6 MB
HeapAlloc: 660 kB HeapInuse: 926 kB TotalAlloc: 4.9 MB
HeapAlloc: 923 kB HeapInuse: 1.2 MB TotalAlloc: 5.1 MB
HeapAlloc: 1.2 MB HeapInuse: 1.4 MB TotalAlloc: 5.4 MB
HeapAlloc: 1.4 MB HeapInuse: 1.7 MB TotalAlloc: 5.7 MB
HeapAlloc: 1.7 MB HeapInuse: 2.0 MB TotalAlloc: 5.9 MB
HeapAlloc: 2.0 MB HeapInuse: 2.2 MB TotalAlloc: 6.2 MB
HeapAlloc: 2.2 MB HeapInuse: 2.5 MB TotalAlloc: 6.5 MB
HeapAlloc: 2.5 MB HeapInuse: 2.8 MB TotalAlloc: 6.7 MB
HeapAlloc: 2.8 MB HeapInuse: 3.0 MB TotalAlloc: 7.0 MB
HeapAlloc: 3.0 MB HeapInuse: 3.3 MB TotalAlloc: 7.2 MB
HeapAlloc: 3.3 MB HeapInuse: 3.5 MB TotalAlloc: 7.5 MB
HeapAlloc: 3.5 MB HeapInuse: 3.8 MB TotalAlloc: 7.8 MB
HeapAlloc: 3.8 MB HeapInuse: 4.1 MB TotalAlloc: 8.0 MB
HeapAlloc: 4.1 MB HeapInuse: 4.3 MB TotalAlloc: 8.3 MB
HeapAlloc: 136 kB HeapInuse: 401 kB TotalAlloc: 8.6 MB
HeapAlloc: 400 kB HeapInuse: 664 kB TotalAlloc: 8.8 MB
HeapAlloc: 662 kB HeapInuse: 926 kB TotalAlloc: 9.1 MB
HeapAlloc: 924 kB HeapInuse: 1.2 MB TotalAlloc: 9.3 MB
HeapAlloc: 1.2 MB HeapInuse: 1.4 MB TotalAlloc: 9.6 MB
HeapAlloc: 1.4 MB HeapInuse: 1.7 MB TotalAlloc: 9.9 MB
HeapAlloc: 1.7 MB HeapInuse: 2.0 MB TotalAlloc: 10 MB
HeapAlloc: 2.0 MB HeapInuse: 2.2 MB TotalAlloc: 10 MB
HeapAlloc: 2.2 MB HeapInuse: 2.5 MB TotalAlloc: 11 MB
HeapAlloc: 2.5 MB HeapInuse: 2.8 MB TotalAlloc: 11 MB
HeapAlloc: 2.8 MB HeapInuse: 3.0 MB TotalAlloc: 11 MB
HeapAlloc: 3.0 MB HeapInuse: 3.3 MB TotalAlloc: 11 MB
HeapAlloc: 3.3 MB HeapInuse: 3.5 MB TotalAlloc: 12 MB
HeapAlloc: 3.5 MB HeapInuse: 3.8 MB TotalAlloc: 12 MB
HeapAlloc: 3.8 MB HeapInuse: 4.1 MB TotalAlloc: 12 MB
HeapAlloc: 4.1 MB HeapInuse: 4.3 MB TotalAlloc: 12 MB
HeapAlloc: 136 kB HeapInuse: 401 kB TotalAlloc: 13 MB
HeapAlloc: 400 kB HeapInuse: 664 kB TotalAlloc: 13 MB
HeapAlloc: 663 kB HeapInuse: 926 kB TotalAlloc: 13 MB
HeapAlloc: 925 kB HeapInuse: 1.2 MB TotalAlloc: 14 MB
HeapAlloc: 1.2 MB HeapInuse: 1.4 MB TotalAlloc: 14 MB
HeapAlloc: 1.4 MB HeapInuse: 1.7 MB TotalAlloc: 14 MB