Move rlimit functions into sys package. (#3824)

This patch addresses below

* go build works for bsd family
* probe total RAM size for bsd family
* make unit testable functions

cmd/server-rlimit.go

@@ -0,0 +1,73 @@
+/*
+ * 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 cmd
+
+import (
+	"github.com/minio/minio/pkg/sys"
+)
+
+func setMaxOpenFiles() error {
+	_, maxLimit, err := sys.GetMaxOpenFileLimit()
+	if err != nil {
+		return err
+	}
+
+	return sys.SetMaxOpenFileLimit(maxLimit, maxLimit)
+}
+
+func getMaxCacheSize(curLimit, totalRAM uint64) (cacheSize uint64) {
+	// Return zero if current limit or totalTAM is less than minRAMSize.
+	if curLimit < minRAMSize || totalRAM < minRAMSize {
+		return cacheSize
+	}
+
+	// Return 50% of current rlimit or total RAM as cache size.
+	if curLimit < totalRAM {
+		cacheSize = curLimit / 2
+	} else {
+		cacheSize = totalRAM / 2
+	}
+
+	return cacheSize
+}
+
+func setMaxMemory() error {
+	// Get max memory limit
+	_, maxLimit, err := sys.GetMaxMemoryLimit()
+	if err != nil {
+		return err
+	}
+
+	// Set max memory limit as current memory limit.
+	if err = sys.SetMaxMemoryLimit(maxLimit, maxLimit); err != nil {
+		return err
+	}
+
+	// Get total RAM.
+	stats, err := sys.GetStats()
+	if err != nil {
+		return err
+	}
+
+	// In some OS like windows, maxLimit is zero.  Set total RAM as maxLimit.
+	if maxLimit == 0 {
+		maxLimit = stats.TotalRAM
+	}
+
+	globalMaxCacheSize = getMaxCacheSize(maxLimit, stats.TotalRAM)
+	return nil
+}