Push max threads to little less than kernel limit (#5001)

Let Minio server use more threads than allowed by golang runtime. This
is important to better deal with high load.

cmd/server-rlimit.go

@@ -16,9 +16,24 @@
 
 package cmd
 
-import "github.com/minio/minio/pkg/sys"
+import (
+	"runtime/debug"
+
+	"github.com/minio/minio/pkg/sys"
+)
 
 func setMaxResources() (err error) {
+	// Set the Go runtime max threads threshold to 90% of kernel setting.
+	// Do not return when an error when encountered since it is not a crucial task.
+	sysMaxThreads, mErr := sys.GetMaxThreads()
+	if mErr == nil {
+		minioMaxThreads := (sysMaxThreads * 90) / 100
+		// Only set max threads if it is greater than the default one
+		if minioMaxThreads > 10000 {
+			debug.SetMaxThreads(minioMaxThreads)
+		}
+	}
+
 	var maxLimit uint64
 
 	// Set open files limit to maximum.

pkg/sys/threads.go

@@ -0,0 +1,38 @@
+// +build linux
+
+/*
+ * Minio Cloud Storage, (C) 2017 Minio, Inc.
+ *
+ * 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.
+ */
+
+package sys
+
+import (
+	"io/ioutil"
+	"strconv"
+	"strings"
+)
+
+// GetMaxThreads returns the maximum number of threads that the system can create.
+func GetMaxThreads() (int, error) {
+	sysMaxThreadsStr, err := ioutil.ReadFile("/proc/sys/kernel/threads-max")
+	if err != nil {
+		return 0, err
+	}
+	sysMaxThreads, err := strconv.Atoi(strings.TrimSpace(string(sysMaxThreadsStr)))
+	if err != nil {
+		return 0, err
+	}
+	return sysMaxThreads, nil
+}

pkg/sys/threads_other.go

@@ -0,0 +1,26 @@
+// +build !linux
+
+/*
+ * Minio Cloud Storage, (C) 2017 Minio, Inc.
+ *
+ * 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.
+ */
+
+package sys
+
+import "errors"
+
+// GetMaxThreads returns the maximum number of threads that the system can create.
+func GetMaxThreads() (int, error) {
+	return 0, errors.New("getting max threads is not supported")
+}