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metric/system/cgroup: introduce cache for cgroup v2
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Signed-off-by: Florian Lehner <[email protected]>
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florianl committed Nov 24, 2023
1 parent dd6d8b7 commit b7e4327
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Showing 2 changed files with 42 additions and 1 deletion.
17 changes: 17 additions & 0 deletions metric/system/cgroup/reader.go
Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,8 @@ import (
"path/filepath"
"strconv"
"strings"
"sync"
"time"

"github.com/elastic/elastic-agent-libs/logp"
"github.com/elastic/elastic-agent-system-metrics/metric/system/cgroup/cgv1"
Expand Down Expand Up @@ -77,6 +79,17 @@ type mount struct {
fullPath string // Absolute path to the cgroup. It's the mountpoint joined with the path.
}

// pathListWithTime combines PathList with a timestamp.
type pathListWithTime struct {
added time.Time
pathList PathList
}

type pathCache struct {
sync.RWMutex
cache map[string]pathListWithTime
}

// Reader reads cgroup metrics and limits.
type Reader struct {
// Mountpoint of the root filesystem. Defaults to / if not set. This can be
Expand All @@ -85,6 +98,9 @@ type Reader struct {
ignoreRootCgroups bool // Ignore a cgroup when its path is "/".
cgroupsHierarchyOverride string
cgroupMountpoints Mountpoints // Mountpoints for each subsystem (e.g. cpu, cpuacct, memory, blkio).

// Cache to map known v2 cgroup controllerPaths to pathListWithTime.
v2ControllerPathCache pathCache
}

// ReaderOptions holds options for NewReaderOptions.
Expand Down Expand Up @@ -135,6 +151,7 @@ func NewReaderOptions(opts ReaderOptions) (*Reader, error) {
ignoreRootCgroups: opts.IgnoreRootCgroups,
cgroupsHierarchyOverride: opts.CgroupsHierarchyOverride,
cgroupMountpoints: mountpoints,
v2ControllerPathCache: pathCache{cache: make(map[string]pathListWithTime)},
}, nil
}

Expand Down
26 changes: 25 additions & 1 deletion metric/system/cgroup/util.go
Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@ import (
"path/filepath"
"strconv"
"strings"
"time"

"github.com/elastic/elastic-agent-libs/logp"
"github.com/elastic/elastic-agent-system-metrics/metric/system/resolve"
Expand Down Expand Up @@ -67,7 +68,7 @@ type PathList struct {

// Flatten combines the V1 and V2 cgroups in cases where we don't need a map with keys
func (pl PathList) Flatten() []ControllerPath {
list := []ControllerPath{}
list := make([]ControllerPath, 0, len(pl.V1)+len(pl.V2))
for _, v1 := range pl.V1 {
list = append(list, v1)
}
Expand Down Expand Up @@ -275,6 +276,23 @@ the container as /sys/fs/cgroup/unified and start the system module with the hos
controllerPath = r.rootfsMountpoint.ResolveHostFS(filepath.Join("/sys/fs/cgroup/unified", path))
}

// Check if there is an entry for controllerPath already cached.
r.v2ControllerPathCache.Lock()
cacheEntry, ok := r.v2ControllerPathCache.cache[controllerPath]
if ok {
// If the cached entry for controllerPath is not older than 5 minutes,
// return the cached entry.
if time.Since(cacheEntry.added) < 5*time.Minute {
cPaths.V2 = cacheEntry.pathList.V2
r.v2ControllerPathCache.Unlock()
continue
}
}
// Consider the existing entry for controllerPath invalid, as it is
// older than 5 minutes.
delete(r.v2ControllerPathCache.cache, controllerPath)
r.v2ControllerPathCache.Unlock()

cgpaths, err := os.ReadDir(controllerPath)
if err != nil {
return cPaths, fmt.Errorf("error fetching cgroupV2 controllers for cgroup location '%s' and path line '%s': %w", r.cgroupMountpoints.V2Loc, line, err)
Expand All @@ -287,6 +305,12 @@ the container as /sys/fs/cgroup/unified and start the system module with the hos
cPaths.V2[controllerName] = ControllerPath{ControllerPath: path, FullPath: controllerPath, IsV2: true}
}
}
r.v2ControllerPathCache.Lock()
r.v2ControllerPathCache.cache[controllerPath] = pathListWithTime{
added: time.Now(),
pathList: cPaths,
}
r.v2ControllerPathCache.Unlock()
// cgroup v1
} else {
subsystems := strings.Split(fields[1], ",")
Expand Down

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