Add more efficient way to find children of a process

resources/psutil/process.go

@@ -36,6 +36,7 @@ type process struct {
 	cpuLimit  uint64
 	ncpu      float64
 	proc      *psprocess.Process
+	procfs    Procfs
 
 	stopTicker context.CancelFunc
 
@@ -57,6 +58,7 @@ func (u *util) Process(pid int32) (Process, error) {
 		cpuLimit:  u.cpuLimit,
 		ncpu:      u.ncpu,
 		gpu:       u.gpu,
+		procfs:    u.procfs,
 	}
 
 	proc, err := psprocess.NewProcess(pid)
@@ -117,13 +119,10 @@ func (p *process) collectCPU() cpuTimesStat {
 func (p *process) collectCPUFromChildren(proc *psprocess.Process) *cpuTimesStat {
 	stat := cpuTimesStat{}
 
-	children, err := proc.Children()
+	children := p.procfs.AllChildren(proc.Pid)
-	if err != nil {
-		return &stat
-	}
 
-	for _, child := range children {
+	for _, pid := range children {
-		cstat, err := cpuTimes(child.Pid)
+		cstat, err := cpuTimes(pid)
 		if err != nil {
 			continue
 		}
@@ -133,14 +132,6 @@ func (p *process) collectCPUFromChildren(proc *psprocess.Process) *cpuTimesStat
 		stat.user += cstat.user
 		stat.idle += cstat.idle
 		stat.other += cstat.other
-
-		cstat = p.collectCPUFromChildren(child)
-
-		stat.total += cstat.total
-		stat.system += cstat.system
-		stat.user += cstat.user
-		stat.idle += cstat.idle
-		stat.other += cstat.other
 	}
 
 	return &stat
@@ -178,22 +169,22 @@ func (p *process) collectMemory() uint64 {
 }
 
 func (p *process) collectMemoryFromChildren(proc *psprocess.Process) uint64 {
-	children, err := proc.Children()
+	children := p.procfs.AllChildren(proc.Pid)
-	if err != nil {
-		return 0
-	}
 
 	rss := uint64(0)
 
-	for _, child := range children {
+	for _, pid := range children {
+		child, err := psprocess.NewProcess(pid)
+		if err != nil {
+			continue
+		}
+
 		info, err := child.MemoryInfo()
 		if err != nil {
 			continue
 		}
 
 		rss += info.RSS
-
-		rss += p.collectMemoryFromChildren(child)
 	}
 
 	return rss

resources/psutil/procfs.go

@@ -0,0 +1,146 @@
+package psutil
+
+import (
+	"bytes"
+	"context"
+	"io/fs"
+	"os"
+	"regexp"
+	"slices"
+	"strconv"
+	"sync"
+	"time"
+)
+
+type Procfs interface {
+	// Children returns all direct children of a process
+	Children(ppid int32) []int32
+
+	// AllChildren returns all children of a process
+	AllChildren(ppid int32) []int32
+}
+
+type procfs struct {
+	children map[int32][]int32
+
+	lock sync.RWMutex
+}
+
+func NewProcfs(ctx context.Context, interval time.Duration) (Procfs, error) {
+	p := &procfs{
+		children: map[int32][]int32{},
+	}
+
+	children, err := p.createChildrenMap()
+	if err != nil {
+		return p, err
+	}
+
+	p.children = children
+
+	go p.ticker(ctx, interval)
+
+	return p, nil
+}
+
+func (p *procfs) Children(ppid int32) []int32 {
+	p.lock.RLock()
+	defer p.lock.RUnlock()
+
+	pids, ok := p.children[ppid]
+	if !ok {
+		return []int32{}
+	}
+
+	return slices.Clone(pids)
+}
+
+func (p *procfs) AllChildren(ppid int32) []int32 {
+	children := p.Children(ppid)
+
+	allchildren := slices.Clone(children)
+
+	for _, child := range children {
+		allchildren = append(allchildren, p.AllChildren(child)...)
+	}
+
+	return allchildren
+}
+
+func (p *procfs) ticker(ctx context.Context, interval time.Duration) {
+	ticker := time.NewTicker(interval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			children, err := p.createChildrenMap()
+			if err == nil {
+				p.lock.Lock()
+				p.children = children
+				p.lock.Unlock()
+			}
+		}
+	}
+}
+
+func (p *procfs) createChildrenMap() (map[int32][]int32, error) {
+	children := map[int32][]int32{}
+	re := regexp.MustCompile(`^[0-9]+$`)
+
+	proc := os.Getenv("HOST_PROC")
+	if proc == "" {
+		proc = "/proc"
+	}
+
+	fs := os.DirFS(proc).(fs.ReadDirFS)
+	dirents, err := fs.ReadDir(".")
+	if err != nil {
+		return nil, err
+	}
+
+	for _, d := range dirents {
+		if !d.IsDir() {
+			continue
+		}
+
+		name := d.Name()
+
+		if !re.MatchString(name) {
+			continue
+		}
+
+		data, err := os.ReadFile(proc + "/" + name + "/stat")
+		if err != nil {
+			continue
+		}
+
+		fields := bytes.Split(data, []byte{' '})
+		if len(fields) < 4 {
+			continue
+		}
+
+		var pid int32 = 0
+		var ppid int32 = 0
+
+		if x, err := strconv.ParseInt(string(fields[3]), 10, 32); err == nil {
+			ppid = int32(x)
+		}
+
+		if x, err := strconv.ParseInt(name, 10, 32); err == nil {
+			pid = int32(x)
+		}
+
+		if pid == 0 {
+			continue
+		}
+
+		c := children[ppid]
+		c = append(c, pid)
+		children[ppid] = c
+	}
+
+	return children, nil
+}

resources/psutil/procfs_test.go

@@ -0,0 +1,41 @@
+package psutil
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestChildren(t *testing.T) {
+	p := &procfs{
+		children: map[int32][]int32{
+			0: {1},
+			1: {2, 3},
+			2: {4, 5, 6},
+			3: {7, 8, 9},
+		},
+	}
+
+	require.Equal(t, []int32{1}, p.Children(0))
+	require.Equal(t, []int32{2, 3}, p.Children(1))
+	require.Equal(t, []int32{4, 5, 6}, p.Children(2))
+	require.Equal(t, []int32{7, 8, 9}, p.Children(3))
+	require.Equal(t, []int32{}, p.Children(4))
+}
+
+func TestAllChildren(t *testing.T) {
+	p := &procfs{
+		children: map[int32][]int32{
+			0: {1},
+			1: {2, 3},
+			2: {4, 5, 6},
+			3: {7, 8, 9},
+		},
+	}
+
+	require.Equal(t, []int32{1, 2, 3, 4, 5, 6, 7, 8, 9}, p.AllChildren(0))
+	require.Equal(t, []int32{2, 3, 4, 5, 6, 7, 8, 9}, p.AllChildren(1))
+	require.Equal(t, []int32{4, 5, 6}, p.AllChildren(2))
+	require.Equal(t, []int32{7, 8, 9}, p.AllChildren(3))
+	require.Equal(t, []int32{}, p.AllChildren(4))
+}

resources/psutil/psutil.go

@@ -137,6 +137,8 @@ type util struct {
 	mem              MemoryInfo
 
 	gpu psutilgpu.GPU
+
+	procfs Procfs
 }
 
 // New returns a new util, it will be started automatically
@@ -184,6 +186,9 @@ func New(root string, gpu psutilgpu.GPU) (Util, error) {
 	go u.tickCPU(ctx, time.Second)
 	go u.tickMemory(ctx, time.Second)
 
+	procfs, _ := NewProcfs(ctx, 5*time.Second)
+	u.procfs = procfs
+
 	u.stopOnce = sync.Once{}
 
 	return u, nil
@@ -224,7 +229,8 @@ func (u *util) detectCgroupVersion() int {
 }
 
 func (u *util) cgroupCPULimit(version int) (uint64, float64) {
-	if version == 1 {
+	switch version {
+	case 1:
 		lines, err := u.readFile("cpu/cpu.cfs_quota_us")
 		if err != nil {
 			return 0, 0
@@ -248,7 +254,7 @@ func (u *util) cgroupCPULimit(version int) (uint64, float64) {
 
 			return uint64(1e6/period*quota) * 1e3, quota / period // nanoseconds
 		}
-	} else if version == 2 {
+	case 2:
 		lines, err := u.readFile("cpu.max")
 		if err != nil {
 			return 0, 0
@@ -437,7 +443,8 @@ func (u *util) CPU() (*CPUInfo, error) {
 func (u *util) cgroupCPUTimes(version int) (*cpuTimesStat, error) {
 	info := &cpuTimesStat{}
 
-	if version == 1 {
+	switch version {
+	case 1:
 		lines, err := u.readFile("cpuacct/cpuacct.usage")
 		if err != nil {
 			return nil, err
@@ -449,7 +456,7 @@ func (u *util) cgroupCPUTimes(version int) (*cpuTimesStat, error) {
 		}
 
 		info.system = usage
-	} else if version == 2 {
+	case 2:
 		lines, err := u.readFile("cpu.stat")
 		if err != nil {
 			return nil, err
@@ -523,7 +530,8 @@ func (u *util) Memory() (*MemoryInfo, error) {
 func (u *util) cgroupVirtualMemory(version int) (*MemoryInfo, error) {
 	info := &MemoryInfo{}
 
-	if version == 1 {
+	switch version {
+	case 1:
 		lines, err := u.readFile("memory/memory.limit_in_bytes")
 		if err != nil {
 			return nil, err
@@ -547,7 +555,7 @@ func (u *util) cgroupVirtualMemory(version int) (*MemoryInfo, error) {
 		info.Total = total
 		info.Available = total - used
 		info.Used = used
-	} else if version == 2 {
+	case 2:
 		lines, err := u.readFile("memory.max")
 		if err != nil {
 			return nil, err