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allocator.go
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allocator.go
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/*
* Copyright 2020 Dgraph Labs, Inc. and Contributors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package z
import (
"bytes"
"fmt"
"math"
"math/bits"
"math/rand"
"strings"
"sync"
"sync/atomic"
"time"
"unsafe"
"github.com/dustin/go-humanize"
)
// Allocator amortizes the cost of small allocations by allocating memory in
// bigger chunks. Internally it uses z.Calloc to allocate memory. Once
// allocated, the memory is not moved, so it is safe to use the allocated bytes
// to unsafe cast them to Go struct pointers. Maintaining a freelist is slow.
// Instead, Allocator only allocates memory, with the idea that finally we
// would just release the entire Allocator.
type Allocator struct {
Tag string
buffers [][]byte
compIdx uint64
Ref uint64
sync.Mutex
}
// allocs keeps references to all Allocators, so we can safely discard them later.
var allocsMu *sync.Mutex
var (
allocRef uint64 //nolint:unused,varcheck,gochecknoglobals,lll,deadcode,revive // adopt fork, do not touch it
allocs map[uint64]*Allocator //nolint:unused,varcheck,gochecknoglobals,lll,deadcode,revive // adopt fork, do not touch it
calculatedLog2 []int //nolint:unused,varcheck,gochecknoglobals,lll,deadcode,revive // adopt fork, do not touch it
)
func init() {
allocsMu = new(sync.Mutex)
allocs = make(map[uint64]*Allocator)
// Set up a unique Ref per process.
rand.Seed(time.Now().UnixNano())
allocRef = uint64(rand.Int63n(1<<16)) << 48
calculatedLog2 = make([]int, 1025)
for i := 1; i <= 1024; i++ {
calculatedLog2[i] = int(math.Log2(float64(i)))
}
}
// NewAllocator creates an allocator starting with the given size.
func NewAllocator(sz int, tag string) *Allocator {
ref := atomic.AddUint64(&allocRef, 1)
// We should not allow a zero sized page because addBufferWithMinSize
// will run into an infinite loop trying to double the pagesize.
if sz < 512 {
sz = 512
}
a := &Allocator{
Ref: ref,
buffers: make([][]byte, 64),
Tag: tag,
}
l2 := uint64(log2(sz))
if bits.OnesCount64(uint64(sz)) > 1 {
l2 += 1
}
a.buffers[0] = Calloc(1<<l2, a.Tag)
allocsMu.Lock()
allocs[ref] = a
allocsMu.Unlock()
return a
}
func (a *Allocator) Reset() {
atomic.StoreUint64(&a.compIdx, 0)
}
func Allocators() string {
allocsMu.Lock()
tags := make(map[string]uint64)
num := make(map[string]int)
for _, ac := range allocs {
tags[ac.Tag] += ac.Allocated()
num[ac.Tag] += 1
}
var buf bytes.Buffer
for tag, sz := range tags {
fmt.Fprintf(&buf, "Tag: %s Num: %d Size: %s . ", tag, num[tag], humanize.IBytes(sz))
}
allocsMu.Unlock()
return buf.String()
}
func (a *Allocator) String() string {
var s strings.Builder
s.WriteString(fmt.Sprintf("Allocator: %x\n", a.Ref))
var cum int
for i, b := range a.buffers {
cum += len(b)
if len(b) == 0 {
break
}
s.WriteString(fmt.Sprintf("idx: %d len: %d cum: %d\n", i, len(b), cum))
}
pos := atomic.LoadUint64(&a.compIdx)
bi, pi := parse(pos)
s.WriteString(fmt.Sprintf("bi: %d pi: %d\n", bi, pi))
s.WriteString(fmt.Sprintf("Size: %d\n", a.Size()))
return s.String()
}
// AllocatorFrom would return the allocator corresponding to the ref.
func AllocatorFrom(ref uint64) *Allocator {
allocsMu.Lock()
a := allocs[ref]
allocsMu.Unlock()
return a
}
func parse(pos uint64) (bufIdx, posIdx int) {
return int(pos >> 32), int(pos & 0xFFFFFFFF)
}
// Size returns the size of the allocations so far.
func (a *Allocator) Size() int {
pos := atomic.LoadUint64(&a.compIdx)
bi, pi := parse(pos)
var sz int
for i, b := range a.buffers {
if i < bi {
sz += len(b)
continue
}
sz += pi
return sz
}
panic("Size should not reach here")
}
func log2(sz int) int {
if sz < len(calculatedLog2) {
return calculatedLog2[sz]
}
pow := 10
sz >>= 10
for sz > 1 {
sz >>= 1
pow++
}
return pow
}
func (a *Allocator) Allocated() uint64 {
var alloc int
for _, b := range a.buffers {
alloc += cap(b)
}
return uint64(alloc)
}
func (a *Allocator) TrimTo(max int) {
var alloc int
for i, b := range a.buffers {
if len(b) == 0 {
break
}
alloc += len(b)
if alloc < max {
continue
}
Free(b)
a.buffers[i] = nil
}
}
// Release would release the memory back. Remember to make this call to avoid memory leaks.
func (a *Allocator) Release() {
if a == nil {
return
}
var alloc int
for _, b := range a.buffers {
if len(b) == 0 {
break
}
alloc += len(b)
Free(b)
}
allocsMu.Lock()
delete(allocs, a.Ref)
allocsMu.Unlock()
}
const maxAlloc = 1 << 30
func (a *Allocator) MaxAlloc() int {
return maxAlloc
}
const nodeAlign = unsafe.Sizeof(uint64(0)) - 1
func (a *Allocator) AllocateAligned(sz int) []byte {
tsz := sz + int(nodeAlign)
out := a.Allocate(tsz)
// We are reusing allocators. In that case, it's important to zero out the memory allocated
// here. We don't always zero it out (in Allocate), because other functions would be immediately
// overwriting the allocated slices anyway (see Copy).
ZeroOut(out, 0, len(out))
addr := uintptr(unsafe.Pointer(&out[0]))
aligned := (addr + nodeAlign) & ^nodeAlign
start := int(aligned - addr)
return out[start : start+sz]
}
func (a *Allocator) Copy(buf []byte) []byte {
if a == nil {
return append([]byte{}, buf...)
}
out := a.Allocate(len(buf))
copy(out, buf)
return out
}
func (a *Allocator) addBufferAt(bufIdx, minSz int) {
for {
if bufIdx >= len(a.buffers) {
panic(fmt.Sprintf("Allocator can not allocate more than %d buffers", len(a.buffers)))
}
if len(a.buffers[bufIdx]) == 0 {
break
}
if minSz <= len(a.buffers[bufIdx]) {
// No need to do anything. We already have a buffer which can satisfy minSz.
return
}
bufIdx++
}
assert(bufIdx > 0)
// We need to allocate a new buffer.
// Make pageSize double of the last allocation.
pageSize := 2 * len(a.buffers[bufIdx-1])
// Ensure pageSize is bigger than sz.
for pageSize < minSz {
pageSize *= 2
}
// If bigger than maxAlloc, trim to maxAlloc.
if pageSize > maxAlloc {
pageSize = maxAlloc
}
buf := Calloc(pageSize, a.Tag)
assert(len(a.buffers[bufIdx]) == 0)
a.buffers[bufIdx] = buf
}
func (a *Allocator) Allocate(sz int) []byte {
if a == nil {
return make([]byte, sz)
}
if sz > maxAlloc {
panic(fmt.Sprintf("Unable to allocate more than %d\n", maxAlloc))
}
if sz == 0 {
return nil
}
for {
pos := atomic.AddUint64(&a.compIdx, uint64(sz))
bufIdx, posIdx := parse(pos)
buf := a.buffers[bufIdx]
if posIdx > len(buf) {
a.Lock()
newPos := atomic.LoadUint64(&a.compIdx)
newBufIdx, _ := parse(newPos)
if newBufIdx != bufIdx {
a.Unlock()
continue
}
a.addBufferAt(bufIdx+1, sz)
atomic.StoreUint64(&a.compIdx, uint64((bufIdx+1)<<32))
a.Unlock()
// We added a new buffer. Let's acquire slice the right way by going back to the top.
continue
}
data := buf[posIdx-sz : posIdx]
return data
}
}
type AllocatorPool struct {
allocCh chan *Allocator
closer *Closer
numGets int64
}
func NewAllocatorPool(sz int) *AllocatorPool {
a := &AllocatorPool{
allocCh: make(chan *Allocator, sz),
closer: NewCloser(1),
}
go a.freeupAllocators()
return a
}
func (p *AllocatorPool) Get(sz int, tag string) *Allocator {
if p == nil {
return NewAllocator(sz, tag)
}
atomic.AddInt64(&p.numGets, 1)
select {
case alloc := <-p.allocCh:
alloc.Reset()
alloc.Tag = tag
return alloc
default:
return NewAllocator(sz, tag)
}
}
func (p *AllocatorPool) Return(a *Allocator) {
if a == nil {
return
}
if p == nil {
a.Release()
return
}
a.TrimTo(400 << 20)
select {
case p.allocCh <- a:
return
default:
a.Release()
}
}
func (p *AllocatorPool) Release() {
if p == nil {
return
}
p.closer.SignalAndWait()
}
func (p *AllocatorPool) freeupAllocators() {
defer p.closer.Done()
ticker := time.NewTicker(2 * time.Second)
defer ticker.Stop()
releaseOne := func() bool {
select {
case alloc := <-p.allocCh:
alloc.Release()
return true
default:
return false
}
}
var last int64
for {
select {
case <-p.closer.HasBeenClosed():
close(p.allocCh)
for alloc := range p.allocCh {
alloc.Release()
}
return
case <-ticker.C:
gets := atomic.LoadInt64(&p.numGets)
if gets != last {
// Some retrievals were made since the last time. So, let's avoid doing a release.
last = gets
continue
}
releaseOne()
}
}
}