Merge pull request opencontainers#250 from hqhq/hq_cgroup_cleanup

Some cgroups cleanup
sithembiso · Sep 9, 2015 · 5731a04 · 5731a04
2 parents 0f85e4e + f2ec7ef
commit 5731a04
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Showing 2 changed files with 19 additions and 9 deletions.
diff --git a/libcontainer/cgroups/fs/apply_raw.go b/libcontainer/cgroups/fs/apply_raw.go
@@ -235,20 +235,20 @@ func getCgroupData(c *configs.Cgroup, pid int) (*data, error) {
 	}, nil
 }
 
-func (raw *data) parent(subsystem, mountpoint, src string) (string, error) {
+func (raw *data) parent(subsystem, mountpoint, root string) (string, error) {
 	initPath, err := cgroups.GetThisCgroupDir(subsystem)
 	if err != nil {
 		return "", err
 	}
-	relDir, err := filepath.Rel(src, initPath)
+	relDir, err := filepath.Rel(root, initPath)
 	if err != nil {
 		return "", err
 	}
 	return filepath.Join(mountpoint, relDir), nil
 }
 
 func (raw *data) path(subsystem string) (string, error) {
-	mnt, src, err := cgroups.FindCgroupMountpointAndSource(subsystem)
+	mnt, root, err := cgroups.FindCgroupMountpointAndRoot(subsystem)
 	// If we didn't mount the subsystem, there is no point we make the path.
 	if err != nil {
 		return "", err
@@ -259,7 +259,7 @@ func (raw *data) path(subsystem string) (string, error) {
 		return filepath.Join(raw.root, filepath.Base(mnt), raw.cgroup), nil
 	}
 
-	parent, err := raw.parent(subsystem, mnt, src)
+	parent, err := raw.parent(subsystem, mnt, root)
 	if err != nil {
 		return "", err
 	}

diff --git a/libcontainer/cgroups/utils.go b/libcontainer/cgroups/utils.go
@@ -21,6 +21,9 @@ const cgroupNamePrefix = "name="
 
 // https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt
 func FindCgroupMountpoint(subsystem string) (string, error) {
+	// We are not using mount.GetMounts() because it's super-inefficient,
+	// parsing it directly sped up x10 times because of not using Sscanf.
+	// It was one of two major performance drawbacks in container start.
 	f, err := os.Open("/proc/self/mountinfo")
 	if err != nil {
 		return "", err
@@ -44,7 +47,7 @@ func FindCgroupMountpoint(subsystem string) (string, error) {
 	return "", NewNotFoundError(subsystem)
 }
 
-func FindCgroupMountpointAndSource(subsystem string) (string, string, error) {
+func FindCgroupMountpointAndRoot(subsystem string) (string, string, error) {
 	f, err := os.Open("/proc/self/mountinfo")
 	if err != nil {
 		return "", "", err
@@ -69,16 +72,23 @@ func FindCgroupMountpointAndSource(subsystem string) (string, string, error) {
 }
 
 func FindCgroupMountpointDir() (string, error) {
-	mounts, err := mount.GetMounts()
+	f, err := os.Open("/proc/self/mountinfo")
 	if err != nil {
 		return "", err
 	}
+	defer f.Close()
 
-	for _, mount := range mounts {
-		if mount.Fstype == "cgroup" {
-			return filepath.Dir(mount.Mountpoint), nil
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		txt := scanner.Text()
+		fields := strings.Split(txt, " ")
+		if fields[7] == "cgroup" {
+			return filepath.Dir(fields[4]), nil
 		}
 	}
+	if err := scanner.Err(); err != nil {
+		return "", err
+	}
 
 	return "", NewNotFoundError("cgroup")
 }