Repository: go
Issue: runtime: high startup address space usage (RLIMIT_AS) on Linux AMD64
Labels: NeedsInvestigation,compiler/runtime

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### What version of Go are you using (`go version`)?

<pre>
$ go version
go version go1.14 linux/amd64
</pre>

### Does this issue reproduce with the latest release?
Yes


### What operating system and processor architecture are you using (`go env`)?


<details><summary><code>go env</code> Output</summary><br><pre>
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/vorvvbgc/.cache/go-build"
GOENV="/home/vorvvbgc/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/vorvvbgc/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/vorvvbgc/go1.14/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/vorvvbgc/go1.14/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build969828813=/tmp/go-build -gno-record-gcc-switches"
</pre></details>

### What did you do?
I am trying to get an FastCGI server running behind an Apache2 webserver on a shared hosting system using the net/http/fcgi library. The webserver is limiting my software to 512MB memory. 

This is the code: https://play.golang.org/p/Z-Gc6icOpw5

### What did you expect to see?
I expect to see "This was generated by Go running as a FastCGI app" on the website generated by the FastCGI server. 


### What did you see instead?
I have modified the sysReserve() function in the runtime to include println() to print out the error code from mmap() and the requested memory size. This is a diff of `src/runtime/mem_linux.go` and my version:
```
157a158,159
>       println(err)
>       println(n)
```

I kept the output in the following output in the hopes that it might be useful.

The application crashes with this trace:
```
0
131072
0
1048576
0
8388608
0
67108864
12
536870912
fatal error: failed to reserve page summary memory

runtime stack:
runtime.throw(0x6f3456, 0x25)
        /home/vorvvbgc/go1.14/go/src/runtime/panic.go:1112 +0x72 fp=0x7ffc17e5b170 sp=0x7ffc17e5b140 pc=0x433a12
runtime.(*pageAlloc).sysInit(0x939428)
        /home/vorvvbgc/go1.14/go/src/runtime/mpagealloc_64bit.go:80 +0x13f fp=0x7ffc17e5b1e8 sp=0x7ffc17e5b170 pc=0x42ac1f
runtime.(*pageAlloc).init(0x939428, 0x939420, 0x94db38)
        /home/vorvvbgc/go1.14/go/src/runtime/mpagealloc.go:297 +0x75 fp=0x7ffc17e5b210 sp=0x7ffc17e5b1e8 pc=0x4288b5
runtime.(*mheap).init(0x939420)
        /home/vorvvbgc/go1.14/go/src/runtime/mheap.go:694 +0x274 fp=0x7ffc17e5b238 sp=0x7ffc17e5b210 pc=0x425ad4
runtime.mallocinit()
        /home/vorvvbgc/go1.14/go/src/runtime/malloc.go:470 +0xff fp=0x7ffc17e5b268 sp=0x7ffc17e5b238 pc=0x40c41f
runtime.schedinit()
        /home/vorvvbgc/go1.14/go/src/runtime/proc.go:545 +0x60 fp=0x7ffc17e5b2c0 sp=0x7ffc17e5b268 pc=0x437100
runtime.rt0_go(0x7ffc17e5b2f8, 0x1, 0x7ffc17e5b2f8, 0x0, 0x7fd2029790ca, 0x1, 0x7ffc17e5cbb6, 0x0, 0x7ffc17e5cbc4, 0x7ffc17e5cbe6, ...)
        /home/vorvvbgc/go1.14/go/src/runtime/asm_amd64.s:214 +0x125 fp=0x7ffc17e5b2c8 sp=0x7ffc17e5b2c0 pc=0x460655
```
The application works fine with golang 1.13.9.

I have no idea how to debug this further.