drivers/raw_exec: enable configuring raw_exec task to have no memory limit (#19670)

* drivers/raw_exec: enable configuring raw_exec task to have no memory limit

This PR makes it possible to configure a raw_exec task to not have an
upper memory limit, which is how the driver would behave pre-1.7.

This is done by setting memory_max = -1. The cluster (or node pool) must
have memory oversubscription enabled.

* cl: add cl

drivers/shared/executor/executor_universal_linux_test.go

@@ -0,0 +1,68 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+//go:build linux
+
+package executor
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/hashicorp/nomad/nomad/structs"
+	"github.com/hashicorp/nomad/plugins/drivers"
+	"github.com/shoenig/test/must"
+)
+
+func Test_computeMemory(t *testing.T) {
+	cases := []struct {
+		memory    int64
+		memoryMax int64
+		expSoft   int64
+		expHard   int64
+	}{
+		{
+			// typical case; only 'memory' is set and that is used as the hard
+			// memory limit
+			memory:    100,
+			memoryMax: 0,
+			expSoft:   0,
+			expHard:   mbToBytes(100),
+		},
+		{
+			// oversub case; both 'memory' and 'memory_max' are set and used as
+			// the soft and hard memory limits
+			memory:    100,
+			memoryMax: 200,
+			expSoft:   mbToBytes(100),
+			expHard:   mbToBytes(200),
+		},
+		{
+			// special oversub case; 'memory' is set and 'memory_max' is set to
+			// -1; which indicates there should be no hard limit (i.e. -1 / max)
+			memory:    100,
+			memoryMax: memoryNoLimit,
+			expSoft:   mbToBytes(100),
+			expHard:   memoryNoLimit,
+		},
+	}
+
+	for _, tc := range cases {
+		name := fmt.Sprintf("(%d,%d)", tc.memory, tc.memoryMax)
+		t.Run(name, func(t *testing.T) {
+			command := &ExecCommand{
+				Resources: &drivers.Resources{
+					NomadResources: &structs.AllocatedTaskResources{
+						Memory: structs.AllocatedMemoryResources{
+							MemoryMB:    tc.memory,
+							MemoryMaxMB: tc.memoryMax,
+						},
+					},
+				},
+			}
+			hard, soft := (*UniversalExecutor)(nil).computeMemory(command)
+			must.Eq(t, tc.expSoft, soft)
+			must.Eq(t, tc.expHard, hard)
+		})
+	}
+}