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reflect: ArrayOf GC prog uses too much memory #10524

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rsc opened this issue Apr 21, 2015 · 2 comments
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reflect: ArrayOf GC prog uses too much memory #10524

rsc opened this issue Apr 21, 2015 · 2 comments
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Go1.5

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@rsc
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rsc commented Apr 21, 2015

This program takes 11 GB of memory. It should use a tiny fixed amount. It's not possible to fix right now, because GC programs are disabled, but when we re-enable them, we should make this work too. This must be fixed for Go 1.5, or else we should unexport reflect.ArrayOf (new since Go 1.4).

package main

import (
    "fmt"
    "reflect"
    "runtime"
)

func main() {
    var m1, m2 runtime.MemStats
    runtime.ReadMemStats(&m1)
    reflect.ArrayOf(1e9, reflect.TypeOf((*byte)(nil)))
    runtime.ReadMemStats(&m2)
    fmt.Printf("%d\n", m2.Sys-m1.Sys)
}
@rsc rsc added this to the Go1.5 milestone Apr 21, 2015
sbinet added a commit to sbinet/golang-go that referenced this issue Apr 21, 2015
@sbinet
reflect: optimize gcprog info for arrays
dd77546 
This change implements insArray and insArrayEnd directives for gcProg types
informations.

Fixes golang#10524.

Change-Id: I57773ae63c0ef6f03ea2325c21fc54d9e7bf21c6
@sbinet
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sbinet commented Apr 21, 2015

I am willing to work on this (it's fun to decipher GC internals).
my WIP is over there: sbinet@dd77546

but I would need some more hand holding, I am afraid.

I started to look at runtime/mbitmaps and cmd/internal/gc/reflect.go... (gengcprog1, proggenarray proggendata, proggenarrayend and genemit seem to be the general areas where one should look at, but I don't see quite clearly how they would translate into reflect.progGC framework)

sbinet added a commit to sbinet/golang-go that referenced this issue Apr 23, 2015
@sbinet
reflect: optimize gcprog info for arrays
b1921b8 
This change implements insArray and insArrayEnd directives for gcProg types
informations.

Fixes golang#10524.

Change-Id: I57773ae63c0ef6f03ea2325c21fc54d9e7bf21c6
@gopherbot
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CL https://golang.org/cl/9888 mentions this issue.

@rsc rsc closed this as completed in 512f75e May 16, 2015
@golang golang locked and limited conversation to collaborators Jun 25, 2016
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