Add system memory metrics in v3 (#19486)

Following memory metrics will be added under /system/memory

- available
- buffers
- cache
- free
- shared
- total
- used
- used_perc

cmd/metrics-v3-system-memory.go

@@ -0,0 +1,65 @@
+// Copyright (c) 2015-2024 MinIO, Inc.
+//
+// # This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package cmd
+
+import (
+	"context"
+)
+
+const (
+	memTotal     = "total"
+	memUsed      = "used"
+	memFree      = "free"
+	memBuffers   = "buffers"
+	memCache     = "cache"
+	memUsedPerc  = "used_perc"
+	memShared    = "shared"
+	memAvailable = "available"
+)
+
+var (
+	memTotalMD     = NewGaugeMD(memTotal, "Total memory on the node")
+	memUsedMD      = NewGaugeMD(memUsed, "Used memory on the node")
+	memUsedPercMD  = NewGaugeMD(memUsedPerc, "Used memory percentage on the node")
+	memFreeMD      = NewGaugeMD(memFree, "Free memory on the node")
+	memBuffersMD   = NewGaugeMD(memBuffers, "Buffers memory on the node")
+	memCacheMD     = NewGaugeMD(memCache, "Cache memory on the node")
+	memSharedMD    = NewGaugeMD(memShared, "Shared memory on the node")
+	memAvailableMD = NewGaugeMD(memAvailable, "Available memory on the node")
+)
+
+// loadMemoryMetrics - `MetricsLoaderFn` for node memory metrics.
+func loadMemoryMetrics(ctx context.Context, m MetricValues, c *metricsCache) error {
+	memMetrics, err := c.memoryMetrics.Get()
+	if err != nil {
+		metricsLogIf(ctx, err)
+		return err
+	}
+
+	m.Set(memTotal, float64(memMetrics.Total))
+	m.Set(memUsed, float64(memMetrics.Used))
+	usedPerc := float64(memMetrics.Used) * 100 / float64(memMetrics.Total)
+	m.Set(memUsedPerc, usedPerc)
+	m.Set(memFree, float64(memMetrics.Free))
+	m.Set(memBuffers, float64(memMetrics.Buffers))
+	m.Set(memCache, float64(memMetrics.Cache))
+	m.Set(memShared, float64(memMetrics.Shared))
+	m.Set(memAvailable, float64(memMetrics.Available))
+
+	return nil
+}