Add /proc/swaps collector (#3428)

* Add /proc/swaps collector

Building on prometheus/procfs#246 this PR is introducing metrics around swap devices.

Today metrics around swap are already available, but they are on the node level.
With this PR, metrics are now available per device.

Relates to: #1890

Signed-off-by: Fabian Deutsch <[email protected]>
Co-authored-by: claude.ai


---------

Signed-off-by: Fabian Deutsch <[email protected]>

Author: fabiand

README.md

@@ -208,6 +208,7 @@ qdisc | Exposes [queuing discipline](https://en.wikipedia.org/wiki/Network_sched
 slabinfo | Exposes slab statistics from `/proc/slabinfo`. Note that permission of `/proc/slabinfo` is usually 0400, so set it appropriately. | Linux
 softirqs | Exposes detailed softirq statistics from `/proc/softirqs`. | Linux
 sysctl | Expose sysctl values from `/proc/sys`. Use `--collector.sysctl.include(-info)` to configure. | Linux
+swap | Expose swap information from `/proc/swaps`. | Linux
 systemd | Exposes service and system status from [systemd](http://www.freedesktop.org/wiki/Software/systemd/). | Linux
 tcpstat | Exposes TCP connection status information from `/proc/net/tcp` and `/proc/net/tcp6`. (Warning: the current version has potential performance issues in high load situations.) | Linux
 wifi | Exposes WiFi device and station statistics. | Linux

collector/fixtures/proc/swaps

@@ -0,0 +1,2 @@
+Filename				Type		Size		Used		Priority
+/dev/zram0                              partition	8388604		76		100

collector/swap_linux.go

@@ -0,0 +1,129 @@
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !noswap
+
+package collector
+
+import (
+	"fmt"
+	"log/slog"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/procfs"
+)
+
+const (
+	swapSubsystem = "swap"
+)
+
+var swapLabelNames = []string{"device", "swap_type"}
+
+type swapCollector struct {
+	fs     procfs.FS
+	logger *slog.Logger
+}
+
+func init() {
+	registerCollector("swap", defaultDisabled, NewSwapCollector)
+}
+
+// NewSwapCollector returns a new Collector exposing swap device statistics.
+func NewSwapCollector(logger *slog.Logger) (Collector, error) {
+	fs, err := procfs.NewFS(*procPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open procfs: %w", err)
+	}
+
+	return &swapCollector{
+		fs:     fs,
+		logger: logger,
+	}, nil
+}
+
+type SwapsEntry struct {
+	Device   string
+	Type     string
+	Priority int
+	Size     int
+	Used     int
+}
+
+func (c *swapCollector) getSwapInfo() ([]SwapsEntry, error) {
+	swaps, err := c.fs.Swaps()
+	if err != nil {
+		return nil, fmt.Errorf("couldn't get proc/swap information: %w", err)
+	}
+
+	metrics := make([]SwapsEntry, 0, len(swaps))
+
+	for _, swap := range swaps {
+		metrics = append(metrics, SwapsEntry{Device: swap.Filename, Type: swap.Type,
+			Priority: swap.Priority, Size: swap.Size, Used: swap.Used})
+	}
+
+	return metrics, nil
+}
+
+func (c *swapCollector) Update(ch chan<- prometheus.Metric) error {
+	swaps, err := c.getSwapInfo()
+	if err != nil {
+		return fmt.Errorf("couldn't get swap information: %w", err)
+	}
+
+	for _, swap := range swaps {
+		swapLabelValues := []string{swap.Device, swap.Type}
+
+		// Export swap size in bytes
+		ch <- prometheus.MustNewConstMetric(
+			prometheus.NewDesc(
+				prometheus.BuildFQName(namespace, swapSubsystem, "size_bytes"),
+				"Swap device size in bytes.",
+				[]string{"device", "swap_type"}, nil,
+			),
+			prometheus.GaugeValue,
+			// Size is provided in kbytes (not bytes), translate to bytes
+			// see https://github.com/torvalds/linux/blob/fd94619c43360eb44d28bd3ef326a4f85c600a07/mm/swapfile.c#L3079-L3080
+			float64(swap.Size*1024),
+			swapLabelValues...,
+		)
+
+		// Export swap used in bytes
+		ch <- prometheus.MustNewConstMetric(
+			prometheus.NewDesc(
+				prometheus.BuildFQName(namespace, swapSubsystem, "used_bytes"),
+				"Swap device used in bytes.",
+				swapLabelNames, nil,
+			),
+			prometheus.GaugeValue,
+			// Swap used is also provided in kbytes, translate to bytes
+			float64(swap.Used*1024),
+			swapLabelValues...,
+		)
+
+		// Export swap priority
+		ch <- prometheus.MustNewConstMetric(
+			prometheus.NewDesc(
+				prometheus.BuildFQName(namespace, swapSubsystem, "priority"),
+				"Swap device priority.",
+				swapLabelNames, nil,
+			),
+			prometheus.GaugeValue,
+			float64(swap.Priority),
+			swapLabelValues...,
+		)
+
+	}
+
+	return nil
+}

collector/swap_linux_test.go

@@ -0,0 +1,58 @@
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !noswap
+// +build !noswap
+
+package collector
+
+import (
+	"io"
+	"log/slog"
+	"testing"
+)
+
+func TestSwap(t *testing.T) {
+	*procPath = "fixtures/proc"
+	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
+
+	collector, err := NewSwapCollector(logger)
+	if err != nil {
+		panic(err)
+	}
+
+	swapInfo, err := collector.(*swapCollector).getSwapInfo()
+	if err != nil {
+		panic(err)
+	}
+
+	if want, got := "/dev/zram0", swapInfo[0].Device; want != got {
+		t.Errorf("want swap device %s, got %s", want, got)
+	}
+
+	if want, got := "partition", swapInfo[0].Type; want != got {
+		t.Errorf("want swap type %s, got %s", want, got)
+	}
+
+	if want, got := 100, swapInfo[0].Priority; want != got {
+		t.Errorf("want swap priority %d, got %d", want, got)
+	}
+
+	if want, got := 8388604, swapInfo[0].Size; want != got {
+		t.Errorf("want swap size %d, got %d", want, got)
+	}
+
+	if want, got := 76, swapInfo[0].Used; want != got {
+		t.Errorf("want swpa used %d, got %d", want, got)
+	}
+}