index:=hash("love") % len(array)

index := hash("Key6") % len(array)

// /usr/local/go/src/runtime/map.go
type hmap struct {
	// Note: the format of the hmap is also encoded in cmd/compile/internal/reflectdata/reflect.go.
	// Make sure this stays in sync with the compiler's definition.
	count     int // # live cells == size of map.  Must be first (used by len() builtin)
	flags     uint8
	B         uint8  // log_2 of # of buckets (can hold up to loadFactor * 2^B items)
	noverflow uint16 // approximate number of overflow buckets; see incrnoverflow for details
	hash0     uint32 // hash seed

	buckets    unsafe.Pointer // array of 2^B Buckets. may be nil if count==0.
	oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing
	nevacuate  uintptr        // progress counter for evacuation (buckets less than this have been evacuated)

	extra *mapextra // optional fields
}

type mapextra struct {
	// If both key and elem do not contain pointers and are inline, then we mark bucket
	// type as containing no pointers. This avoids scanning such maps.
	// However, bmap.overflow is a pointer. In order to keep overflow buckets
	// alive, we store pointers to all overflow buckets in hmap.extra.overflow and hmap.extra.oldoverflow.
	// overflow and oldoverflow are only used if key and elem do not contain pointers.
	// overflow contains overflow buckets for hmap.buckets.
	// oldoverflow contains overflow buckets for hmap.oldbuckets.
	// The indirection allows to store a pointer to the slice in hiter.
	overflow    *[]*bmap
	oldoverflow *[]*bmap

	// nextOverflow holds a pointer to a free overflow bucket.
	nextOverflow *bmap
}

type bmap struct {
    topbits  [8]uint8
    keys     [8]keytype
    values   [8]valuetype
    pad      uintptr
    overflow uintptr
}

v:=hash[key]
v,ok:=hash[key]

if h.flags&hashWriting != 0 {
		throw("concurrent map writes")
	}
	hash := t.hasher(key, uintptr(h.hash0))

.........

b := (*bmap)(add(h.buckets, bucket*uintptr(t.bucketsize)))
	top := tophash(hash)

bucketloop:
	for {
		for i := uintptr(0); i < bucketCnt; i++ {
			if b.tophash[i] != top {
				if isEmpty(b.tophash[i]) && inserti == nil {
					inserti = &b.tophash[i]
					insertk = add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
					elem = add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
				}
				if b.tophash[i] == emptyRest {
					break bucketloop
				}
				continue
			}
			k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
			if t.indirectkey() {
				k = *((*unsafe.Pointer)(k))
			}
			if !t.key.equal(key, k) {
				continue
			}
			// already have a mapping for key. Update it.
			if t.needkeyupdate() {
				typedmemmove(t.key, k, key)
			}
			elem = add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
			goto done
		}
		ovf := b.overflow(t)
		if ovf == nil {
			break
		}
		b = ovf
	}

fmt.Println(math.Ceil(math.Log2(float64(1000000) / 6.5)))

package main

import (
	"fmt"
	"runtime"
)

const N = 128

func randBytes() [N]byte {
	return [N]byte{}
}

func printAlloc() {
	var m runtime.MemStats
	runtime.ReadMemStats(&m)
	fmt.Printf("%d MB\n", m.Alloc/1024/1024)
}

func main() {
	n := 1_000_000
	m := make(map[int][N]byte, 0)
	printAlloc()

	for i := 0; i < n; i++ {
		m[i] = randBytes()
	}
	printAlloc()

	for i := 0; i < n; i++ {
		delete(m, i)
	}

	runtime.GC()
	printAlloc()
  // 避免m被GC掉
	runtime.KeepAlive(m)
}

▶ ./t     
0 MB
461 MB
293 MB

package main

import (
	"fmt"
	"runtime"
)

const N = 128

func printAlloc() {
	var m runtime.MemStats
	runtime.ReadMemStats(&m)
	fmt.Printf("%d MB\n", m.Alloc/1024/1024)
}

func main() {
	n := 1_000_000
	m := make(map[int][N]byte, n)
	printAlloc()

	runtime.KeepAlive(m)
}

▶ go run main.go
293 MB

package main

import (
	"fmt"
	"runtime"
)

const N = 128

func randBytes() [N]byte {
	return [N]byte{}
}

func printAlloc() {
	var m runtime.MemStats
	runtime.ReadMemStats(&m)
	fmt.Printf("%d MB\n", m.Alloc/1024/1024)
}

func main() {
	n := 1_000_000
  // 指定初始化容量
	m := make(map[int][N]byte, n)
	printAlloc()

	for i := 0; i < n; i++ {
		m[i] = randBytes()
	}
	printAlloc()

	for i := 0; i < n; i++ {
		delete(m, i)
	}

	runtime.GC()
	printAlloc()
  // 避免m被GC掉
	runtime.KeepAlive(m)
}

▶ go run main.go
293 MB
293 MB
293 MB

0 MB
197 MB
38 MB

func randBytes() *[N]byte {
	return &[N]byte{}
}

	m := make(map[int]*[N]byte, 0)
	
		for i := 0; i < n; i++ {
		m[i] = randBytes()
	}