Add /proc/swaps collector

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)
+	}
+}