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https://github.com/tailscale/tailscale.git
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metrics: optimize CurrentFDs to not allocate on Linux
It was 50% of our allocs on one of our servers. (!!) Updates #2784 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
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@ -32,7 +32,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
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tailscale.com/ipn from tailscale.com/cmd/tailscale/cli+
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tailscale.com/ipn from tailscale.com/cmd/tailscale/cli+
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tailscale.com/ipn/ipnstate from tailscale.com/cmd/tailscale/cli+
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tailscale.com/ipn/ipnstate from tailscale.com/cmd/tailscale/cli+
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tailscale.com/kube from tailscale.com/ipn
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tailscale.com/kube from tailscale.com/ipn
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tailscale.com/metrics from tailscale.com/derp
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💣 tailscale.com/metrics from tailscale.com/derp
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tailscale.com/net/dnscache from tailscale.com/derp/derphttp
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tailscale.com/net/dnscache from tailscale.com/derp/derphttp
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tailscale.com/net/flowtrack from tailscale.com/wgengine/filter+
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tailscale.com/net/flowtrack from tailscale.com/wgengine/filter+
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💣 tailscale.com/net/interfaces from tailscale.com/cmd/tailscale/cli+
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💣 tailscale.com/net/interfaces from tailscale.com/cmd/tailscale/cli+
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@ -112,7 +112,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
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tailscale.com/logtail from tailscale.com/logpolicy
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tailscale.com/logtail from tailscale.com/logpolicy
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tailscale.com/logtail/backoff from tailscale.com/control/controlclient+
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tailscale.com/logtail/backoff from tailscale.com/control/controlclient+
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tailscale.com/logtail/filch from tailscale.com/logpolicy
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tailscale.com/logtail/filch from tailscale.com/logpolicy
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tailscale.com/metrics from tailscale.com/derp
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💣 tailscale.com/metrics from tailscale.com/derp
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tailscale.com/net/dns from tailscale.com/ipn/ipnlocal+
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tailscale.com/net/dns from tailscale.com/ipn/ipnlocal+
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tailscale.com/net/dns/resolver from tailscale.com/wgengine+
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tailscale.com/net/dns/resolver from tailscale.com/wgengine+
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tailscale.com/net/dnscache from tailscale.com/control/controlclient+
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tailscale.com/net/dnscache from tailscale.com/control/controlclient+
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@ -4,10 +4,104 @@
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package metrics
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package metrics
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import "os"
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import (
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"fmt"
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"log"
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"syscall"
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"unsafe"
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)
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func currentFDs() int {
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func currentFDs() int {
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// TODO(bradfitz): do this without so many allocations on Linux.
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fd, err := openProcSelfFD()
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ents, _ := os.ReadDir("/proc/self/fd")
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if err != nil {
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return len(ents)
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return 0
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}
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defer syscall.Close(fd)
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count := 0
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const blockSize = 8 << 10
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buf := make([]byte, blockSize) // stack-allocated; doesn't escape
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bufp := 0 // starting read position in buf
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nbuf := 0 // end valid data in buf
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dirent := &syscall.Dirent{}
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for {
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if bufp >= nbuf {
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bufp = 0
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nbuf, err = readDirent(fd, buf)
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if err != nil {
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log.Printf("currentFDs: readDirent: %v", err)
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return 0
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}
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if nbuf <= 0 {
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return count
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}
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}
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consumed, name := parseDirEnt(dirent, buf[bufp:nbuf])
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bufp += consumed
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if len(name) == 0 || string(name) == "." || string(name) == ".." {
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continue
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}
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count++
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}
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}
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func direntNamlen(dirent *syscall.Dirent) int {
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const fixedHdr = uint16(unsafe.Offsetof(syscall.Dirent{}.Name))
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limit := dirent.Reclen - fixedHdr
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const dirNameLen = 256 // sizeof syscall.Dirent.Name
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if limit > dirNameLen {
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limit = dirNameLen
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}
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for i := uint16(0); i < limit; i++ {
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if dirent.Name[i] == 0 {
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return int(i)
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}
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}
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panic("failed to find terminating 0 byte in dirent")
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}
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func parseDirEnt(dirent *syscall.Dirent, buf []byte) (consumed int, name []byte) {
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// golang.org/issue/37269
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copy(unsafe.Slice((*byte)(unsafe.Pointer(dirent)), unsafe.Sizeof(syscall.Dirent{})), buf)
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if v := unsafe.Offsetof(dirent.Reclen) + unsafe.Sizeof(dirent.Reclen); uintptr(len(buf)) < v {
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panic(fmt.Sprintf("buf size of %d smaller than dirent header size %d", len(buf), v))
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}
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if len(buf) < int(dirent.Reclen) {
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panic(fmt.Sprintf("buf size %d < record length %d", len(buf), dirent.Reclen))
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}
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consumed = int(dirent.Reclen)
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if dirent.Ino == 0 { // File absent in directory.
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return
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}
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name = unsafe.Slice((*byte)(unsafe.Pointer(&dirent.Name[0])), direntNamlen(dirent))
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return
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}
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var procSelfFDName = []byte("/proc/self/fd\x00")
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func openProcSelfFD() (fd int, err error) {
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for {
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r0, _, e1 := syscall.Syscall(syscall.SYS_OPEN,
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uintptr(unsafe.Pointer(&procSelfFDName[0])),
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0, 0)
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if e1 == 0 {
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return int(r0), nil
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}
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if e1 == syscall.EINTR {
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// Since https://golang.org/doc/go1.14#runtime we
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// need to loop on EINTR on more places.
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continue
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}
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return 0, syscall.Errno(e1)
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}
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}
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func readDirent(fd int, buf []byte) (n int, err error) {
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for {
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nbuf, err := syscall.ReadDirent(fd, buf)
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if err != syscall.EINTR {
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return nbuf, err
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}
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}
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}
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}
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@ -5,6 +5,7 @@
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package metrics
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package metrics
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import (
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import (
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"os"
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"runtime"
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"runtime"
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"testing"
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"testing"
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)
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)
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@ -13,10 +14,31 @@ func TestCurrentFileDescriptors(t *testing.T) {
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if runtime.GOOS != "linux" {
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if runtime.GOOS != "linux" {
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t.Skipf("skipping on %v", runtime.GOOS)
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t.Skipf("skipping on %v", runtime.GOOS)
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}
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}
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if n := CurrentFDs(); n < 3 {
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n := CurrentFDs()
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t.Errorf("got %v; want >= 3", n)
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if n < 3 {
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} else {
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t.Fatalf("got %v; want >= 3", n)
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t.Logf("got %v", n)
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}
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allocs := int(testing.AllocsPerRun(100, func() {
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n = CurrentFDs()
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}))
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if allocs != 0 {
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t.Errorf("allocs = %v; want 0", allocs)
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}
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// Open some FDs.
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const extra = 10
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for i := 0; i < extra; i++ {
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f, err := os.Open("/proc/self/stat")
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if err != nil {
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t.Fatal(err)
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}
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defer f.Close()
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}
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n2 := CurrentFDs()
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if n2 != n+extra {
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t.Errorf("fds changed from %v => %v, want to %v", n, n2, n+extra)
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}
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}
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}
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}
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