英文:
Huge GC perforamance problems with big allocated data blocks
问题
我刚刚注意到,如果在程序中分配一个巨大的内存块,垃圾回收器(GC)会占用程序的所有时间。
以下是一个示例代码:
func main() {
//////////////// !!!!!!!
/* 如果我取消下面两行的注释,程序将运行得很快 */
nodesPool := make([]int, 300e6, 300e6)
_ = nodesPool
//////////////////////7
file, _ := os.Open("result.txt")
defer file.Close()
reader := bufio.NewReader(file)
var lastLinkIdx = 1 // 不使用第一个元素,使用0作为保留值
cnt := 0
totalB := 0
for {
l, err := reader.ReadString('\n')
if err == io.EOF {
fmt.Println("EOF")
break
}
cnt += 1
totalB += len(l)
lines := strings.Split(l, ":")
nodeId, _ := strconv.Atoi(lines[0])
_ = nodeId
linkIdsStr := strings.Split(lines[1], ",")
var ii = len(linkIdsStr)
_ = ii
/* ... */
}
fmt.Println("pool ", cnt, totalB, lastLinkIdx)
}
我认为垃圾回收器尝试以某种方式移动巨大的内存块,实际上是否可能在垃圾回收器之外分配内存,但仍然让垃圾回收器为所有其他库提供服务,因为即使是ReadLine
也需要它。
以下是带有内存块的性能分析结果:
Total: 1445 samples
428 29.6% 29.6% 722 50.0% runtime.sweepone
375 26.0% 55.6% 375 26.0% markroot
263 18.2% 73.8% 263 18.2% runtime.xadd
116 8.0% 81.8% 116 8.0% strings.Count
98 6.8% 88.6% 673 46.6% strings.genSplit
34 2.4% 90.9% 44 3.0% runtime.MSpan_Sweep
25 1.7% 92.7% 729 50.4% MCentral_Grow
17 1.2% 93.8% 19 1.3% syscall.Syscall
9 0.6% 94.5% 9 0.6% runtime.memclr
9 0.6% 95.1% 9 0.6% runtime.memmove
以下是没有内存块的性能分析结果:
98 27.0% 27.0% 98 27.0% strings.Count
93 25.6% 52.6% 228 62.8% strings.genSplit
45 12.4% 65.0% 45 12.4% scanblock
24 6.6% 71.6% 28 7.7% runtime.MSpan_Sweep
13 3.6% 75.2% 74 20.4% runtime.mallocgc
12 3.3% 78.5% 12 3.3% runtime.memclr
8 2.2% 80.7% 8 2.2% MHeap_ReclaimList
8 2.2% 82.9% 11 3.0% syscall.Syscall
6 1.7% 84.6% 44 12.1% MHeap_Reclaim
6 1.7% 86.2% 6 1.7% markonly
希望对你有所帮助!
英文:
I have just noticed that if I allocate a huge memory block in programm. GC will eat all programm time.
Here is POC.
https://gist.github.com/martende/252f403f0c17cb489de4
func main() {
//////////////// !!!!!!!
/* If I uncomment 2 lines below programm runs fast */
nodesPool := make([]int, 300e6, 300e6)
_ = nodesPool
//////////////////////7
file, _ := os.Open("result.txt")
defer file.Close()
reader := bufio.NewReader(file)
var lastLinkIdx = 1 // Dont use first element use 0 as saver
cnt:= 0
totalB := 0
for {
l, err := reader.ReadString('\n')
if err == io.EOF {
fmt.Println("EOF")
break
}
cnt+=1
totalB+=len(l)
lines := strings.Split(l, ":")
nodeId,_ := strconv.Atoi(lines[0])
_ = nodeId
linkIdsStr := strings.Split(lines[1], ",")
var ii = len(linkIdsStr)
_ = ii
/* ... */
}
fmt.Println("pool ",cnt,totalB,lastLinkIdx)
}
I think that GC tries somehow move the huge memory block , is it actually possible to allocate memory out of GC but leave GC for all other libraries becuase even ReadLine need it.
Here is profiling with memory block.
Total: 1445 samples
428 29.6% 29.6% 722 50.0% runtime.sweepone
375 26.0% 55.6% 375 26.0% markroot
263 18.2% 73.8% 263 18.2% runtime.xadd
116 8.0% 81.8% 116 8.0% strings.Count
98 6.8% 88.6% 673 46.6% strings.genSplit
34 2.4% 90.9% 44 3.0% runtime.MSpan_Sweep
25 1.7% 92.7% 729 50.4% MCentral_Grow
17 1.2% 93.8% 19 1.3% syscall.Syscall
9 0.6% 94.5% 9 0.6% runtime.memclr
9 0.6% 95.1% 9 0.6% runtime.memmove
Here is profiling without memory block.
98 27.0% 27.0% 98 27.0% strings.Count
93 25.6% 52.6% 228 62.8% strings.genSplit
45 12.4% 65.0% 45 12.4% scanblock
24 6.6% 71.6% 28 7.7% runtime.MSpan_Sweep
13 3.6% 75.2% 74 20.4% runtime.mallocgc
12 3.3% 78.5% 12 3.3% runtime.memclr
8 2.2% 80.7% 8 2.2% MHeap_ReclaimList
8 2.2% 82.9% 11 3.0% syscall.Syscall
6 1.7% 84.6% 44 12.1% MHeap_Reclaim
6 1.7% 86.2% 6 1.7% markonly
答案1
得分: 1
Dmitry Vyukov来自Go团队,他在这里表示这是一个Go运行时性能问题,你可以通过大量分配来触发该问题,并且作为一种解决方法,"你可以在大对象变为死对象后立即收集它,并在此之后增加GOGC的值。"
广义上来说,GitHub上的问题指出运行时创建了许多内存管理结构(spans),然后无限期地保留它们,并且在每次垃圾回收时都需要进行清理。根据问题标签,修复计划定于Go 1.5版本。
他提供的解决方法示例代码如下:
package main
import (
"runtime"
"runtime/debug"
)
var x = make([]byte, 1<<20)
var y []byte
var z []byte
func main() {
y = make([]byte, 1<<30)
y = nil
runtime.GC()
debug.SetGCPercent(1000)
for i := 0; i < 1e6; i++ {
z = make([]byte, 8192)
}
}
(一些评论是关于完全不同的答案和代码示例,专注于避免分配,我已经将它们编辑掉了。没有办法“告诉”StackOverflow这是一个新的答案,所以它们仍然存在。)
英文:
Dmitry Vyukov of the Go team says this is a Go runtime performance issue you can trigger with a huge allocation, and that as a workaround, "you can collect the large object as soon as it become
Broadly, the GitHub issue says that the runtime creates a lot of memory-management structures (spans) that it then keeps around indefinitely and has to sweep on every GC. Going by the issue tags, a fix is targeted for Go 1.5.
His sample with workaround is:
package main
import (
"runtime"
"runtime/debug"
)
var x = make([]byte, 1<<20)
var y []byte
var z []byte
func main() {
y = make([]byte, 1<<30)
y = nil
runtime.GC()
debug.SetGCPercent(1000)
for i := 0; i < 1e6; i++ {
z = make([]byte, 8192)
}
}
(Some comments are about a totally different answer and code sample focused on avoiding allocations that I've edited out. There's no way to "tell" StackOverflow this is a new answer, so they remain.)
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