Open
Description
Go version
go1.23.4 linux/amd64
Output of go env in your module/workspace:
GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/ykelani/.cache/go-build'
GOENV='/home/ykelani/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/ykelani/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/ykelani/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/ykelani/sdk/go1.23.4'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/ykelani/sdk/go1.23.4/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.23.4'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/ykelani/.config/go/telemetry'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/ykelani/TestCGoScaling/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build4071249400=/tmp/go-build -gno-record-gcc-switches'What did you do?
package main
/*
#cgo CFLAGS: -O0
#include <unistd.h>
void a(int depth) {
if (depth > 0) a(depth - 1);
}
*/
import "C"
import (
"fmt"
"runtime/debug"
"sync"
)
func main() {
fmt.Println("Running multiple CGo calls")
var wg sync.WaitGroup
for i := 0; i < 1000000; i++ {
go func() {
wg.Add(1)
defer wg.Done()
C.a(100000)
}()
}
wg.Wait()
debug.FreeOSMemory()
select {}
}
What did you see happen?
After the program pauses on the select call, RSS is 497MB for 150 OS threads. I see many segments of size 3132KB in the pmap output - my uninformed guess is that these are thread stacks but it's unclear why they are still in physical memory.
dev-dsk-ykelani-1a-f1f9d672 % ps -o nlwp 15514
NLWP
150
dev-dsk-ykelani-1a-f1f9d672 % pmap -x 15514
15514: ./build/bin/cgo-scaling
Address Kbytes RSS Dirty Mode Mapping
0000000000400000 1352 1352 0 r-x-- cgo-scaling
0000000000751000 4 4 4 r---- cgo-scaling
0000000000752000 44 44 20 rw--- cgo-scaling
000000000075d000 144 72 72 rw--- [ anon ]
00000000120cf000 132 8 8 rw--- [ anon ]
000000c000000000 65536 28900 28900 rw--- [ anon ]
00007fbeb51f5000 4 0 0 ----- [ anon ]
00007fbeb51f6000 10240 3132 3132 rw--- [ anon ]
00007fbeb5bf6000 4 0 0 ----- [ anon ]
00007fbeb5bf7000 10240 3132 3132 rw--- [ anon ]
00007fbeb65f7000 4 0 0 ----- [ anon ]
00007fbeb65f8000 10240 3132 3132 rw--- [ anon ]
00007fbeb6ff8000 4 0 0 ----- [ anon ]
00007fbeb6ff9000 10240 3132 3132 rw--- [ anon ]
00007fbeb79f9000 4 0 0 ----- [ anon ]
00007fbeb79fa000 10240 3132 3132 rw--- [ anon ]
00007fbeb83fa000 4 0 0 ----- [ anon ]
00007fbeb83fb000 10240 3132 3132 rw--- [ anon ]
00007fbeb8dfb000 4 0 0 ----- [ anon ]
00007fbeb8dfc000 10240 3132 3132 rw--- [ anon ]
00007fbeb97fc000 4 0 0 ----- [ anon ]
00007fbeb97fd000 10240 3132 3132 rw--- [ anon ]
00007fbeba1fd000 4 0 0 ----- [ anon ]
00007fbeba1fe000 10240 3132 3132 rw--- [ anon ]
00007fbebabfe000 4 0 0 ----- [ anon ]
00007fbebabff000 10240 3132 3132 rw--- [ anon ]
00007fbebb5ff000 4 0 0 ----- [ anon ]
00007fbebb600000 10240 3132 3132 rw--- [ anon ]
00007fbebc000000 132 4 4 rw--- [ anon ]
00007fbebc021000 65404 0 0 ----- [ anon ]
00007fbec0000000 132 4 4 rw--- [ anon ]
00007fbec0021000 65404 0 0 ----- [ anon ]
00007fbec4000000 132 4 4 rw--- [ anon ]
00007fbec4021000 65404 0 0 ----- [ anon ]
00007fbec83fa000 4 0 0 ----- [ anon ]
...
00007fc1117e5000 10496 3296 3296 rw--- [ anon ]
00007fc112225000 4 0 0 ----- [ anon ]
00007fc112226000 10240 3132 3132 rw--- [ anon ]
00007fc112c26000 4 0 0 ----- [ anon ]
00007fc112c27000 10240 3132 3132 rw--- [ anon ]
00007fc113627000 4 0 0 ----- [ anon ]
00007fc113628000 10240 8 8 rw--- [ anon ]
00007fc114028000 33792 8 8 rw--- [ anon ]
00007fc116128000 263680 0 0 ----- [ anon ]
00007fc1262a8000 4 4 4 rw--- [ anon ]
00007fc1262a9000 524284 0 0 ----- [ anon ]
00007fc1462a8000 4 4 4 rw--- [ anon ]
00007fc1462a9000 293564 0 0 ----- [ anon ]
00007fc158158000 4 4 4 rw--- [ anon ]
00007fc158159000 36692 0 0 ----- [ anon ]
00007fc15a52e000 4 4 4 rw--- [ anon ]
00007fc15a52f000 4068 0 0 ----- [ anon ]
00007fc15a928000 1680 1184 0 r-x-- libc-2.26.so
00007fc15aacc000 2044 0 0 ----- libc-2.26.so
00007fc15accb000 16 16 16 r---- libc-2.26.so
00007fc15accf000 8 8 8 rw--- libc-2.26.so
00007fc15acd1000 16 12 12 rw--- [ anon ]
00007fc15acd5000 96 96 0 r-x-- libpthread-2.26.so
00007fc15aced000 2048 0 0 ----- libpthread-2.26.so
00007fc15aeed000 4 4 4 r---- libpthread-2.26.so
00007fc15aeee000 4 4 4 rw--- libpthread-2.26.so
00007fc15aeef000 16 4 4 rw--- [ anon ]
00007fc15aef3000 144 144 0 r-x-- ld-2.26.so
00007fc15af22000 516 332 332 rw--- [ anon ]
00007fc15afa3000 512 0 0 ----- [ anon ]
00007fc15b023000 4 4 4 rw--- [ anon ]
00007fc15b024000 508 0 0 ----- [ anon ]
00007fc15b0a3000 404 76 76 rw--- [ anon ]
00007fc15b116000 4 4 4 r---- ld-2.26.so
00007fc15b117000 4 4 4 rw--- ld-2.26.so
00007fc15b118000 4 4 4 rw--- [ anon ]
00007ffc4edb4000 3136 3136 3136 rw--- [ stack ]
00007ffc4f17d000 16 0 0 r---- [ anon ]
00007ffc4f181000 8 4 0 r-x-- [ anon ]
ffffffffff600000 4 0 0 r-x-- [ anon ]
---------------- ------- ------- -------
total kB 11088092 497548 494744
What did you expect to see?
RSS to fall much lower for the process - low enough just to support the Go runtime. This is a toy example but I'm seeing the same behaviour slowly "leak" memory for a real long-lived Go process that uses CGo.
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