From 2544b1051ec1bff91d436250ce78295f3123a356 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Felix=20Geisend=C3=B6rfer?=
 <felix.geisendoerfer@datadoghq.com>
Date: Tue, 23 May 2023 11:16:28 +0200
Subject: [PATCH] runtime/metrics: add /gc/gomemlimit:bytes
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For #56857

Change-Id: I184d752cc615874ada3d0dbc6ed1bf72c8debd0f
Reviewed-on: https://go-review.googlesource.com/c/go/+/497316
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Felix Geisendörfer <felix.geisendoerfer@datadoghq.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: David Chase <drchase@google.com>
---
 src/runtime/metrics.go             | 6 ++++++
 src/runtime/metrics/description.go | 7 +++++++
 src/runtime/metrics/doc.go         | 5 +++++
 src/runtime/metrics_test.go        | 8 ++++++++
 4 files changed, 26 insertions(+)

diff --git a/src/runtime/metrics.go b/src/runtime/metrics.go
index ad6348136e..9308a784b7 100644
--- a/src/runtime/metrics.go
+++ b/src/runtime/metrics.go
@@ -248,6 +248,12 @@ func initMetrics() {
 				out.scalar = in.sysStats.heapGoal
 			},
 		},
+		"/gc/gomemlimit:bytes": {
+			compute: func(in *statAggregate, out *metricValue) {
+				out.kind = metricKindUint64
+				out.scalar = uint64(gcController.memoryLimit.Load())
+			},
+		},
 		"/gc/heap/live:bytes": {
 			deps: makeStatDepSet(heapStatsDep),
 			compute: func(in *statAggregate, out *metricValue) {
diff --git a/src/runtime/metrics/description.go b/src/runtime/metrics/description.go
index f5b1020271..e9c8ccc0fe 100644
--- a/src/runtime/metrics/description.go
+++ b/src/runtime/metrics/description.go
@@ -193,6 +193,13 @@ var allDesc = []Description{
 		Kind:        KindUint64,
 		Cumulative:  true,
 	},
+	{
+		Name: "/gc/gomemlimit:bytes",
+		Description: "Go runtime memory limit configured by the user, otherwise " +
+			"math.MaxInt64. This value is set by the GOMEMLIMIT environment variable, and " +
+			"the runtime/debug.SetMemoryLimit function.",
+		Kind: KindUint64,
+	},
 	{
 		Name: "/gc/heap/allocs-by-size:bytes",
 		Description: "Distribution of heap allocations by approximate size. " +
diff --git a/src/runtime/metrics/doc.go b/src/runtime/metrics/doc.go
index fe0d1f58e9..61326ed1df 100644
--- a/src/runtime/metrics/doc.go
+++ b/src/runtime/metrics/doc.go
@@ -147,6 +147,11 @@ Below is the full list of supported metrics, ordered lexicographically.
 	/gc/cycles/total:gc-cycles
 		Count of all completed GC cycles.
 
+	/gc/gomemlimit:bytes
+		Go runtime memory limit configured by the user, otherwise
+		math.MaxInt64. This value is set by the GOMEMLIMIT environment
+		variable, and the runtime/debug.SetMemoryLimit function.
+
 	/gc/heap/allocs-by-size:bytes
 		Distribution of heap allocations by approximate size.
 		Bucket counts increase monotonically. Note that this does not
diff --git a/src/runtime/metrics_test.go b/src/runtime/metrics_test.go
index c1a991ead0..19888376a4 100644
--- a/src/runtime/metrics_test.go
+++ b/src/runtime/metrics_test.go
@@ -7,6 +7,7 @@ package runtime_test
 import (
 	"reflect"
 	"runtime"
+	"runtime/debug"
 	"runtime/metrics"
 	"sort"
 	"strings"
@@ -31,6 +32,11 @@ func TestReadMetrics(t *testing.T) {
 	// Run a GC cycle to get some of the stats to be non-zero.
 	runtime.GC()
 
+	// Set an arbitrary memory limit to check the metric for it
+	limit := int64(512 * 1024 * 1024)
+	oldLimit := debug.SetMemoryLimit(limit)
+	defer debug.SetMemoryLimit(oldLimit)
+
 	// Tests whether readMetrics produces values aligning
 	// with ReadMemStats while the world is stopped.
 	var mstats runtime.MemStats
@@ -138,6 +144,8 @@ func TestReadMetrics(t *testing.T) {
 				// Might happen if we don't call runtime.GC() above.
 				t.Error("live bytes is 0")
 			}
+		case "/gc/gomemlimit:bytes":
+			checkUint64(t, name, samples[i].Value.Uint64(), uint64(limit))
 		case "/gc/heap/objects:objects":
 			checkUint64(t, name, samples[i].Value.Uint64(), mstats.HeapObjects)
 		case "/gc/heap/goal:bytes":
-- 
2.50.0