Break down groups into subsystems

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

cgroups/fs/memory.go

@@ -0,0 +1,41 @@
+package fs
+
+import (
+	"os"
+	"strconv"
+)
+
+type memoryGroup struct {
+}
+
+func (s *memoryGroup) Set(d *data) error {
+	dir, err := d.join("memory")
+	// only return an error for memory if it was not specified
+	if err != nil && (d.c.Memory != 0 || d.c.MemorySwap != 0) {
+		return err
+	}
+	defer func() {
+		if err != nil {
+			os.RemoveAll(dir)
+		}
+	}()
+
+	if d.c.Memory != 0 || d.c.MemorySwap != 0 {
+		if d.c.Memory != 0 {
+			if err := writeFile(dir, "memory.limit_in_bytes", strconv.FormatInt(d.c.Memory, 10)); err != nil {
+				return err
+			}
+			if err := writeFile(dir, "memory.soft_limit_in_bytes", strconv.FormatInt(d.c.Memory, 10)); err != nil {
+				return err
+			}
+		}
+		// By default, MemorySwap is set to twice the size of RAM.
+		// If you want to omit MemorySwap, set it to `-1'.
+		if d.c.MemorySwap != -1 {
+			if err := writeFile(dir, "memory.memsw.limit_in_bytes", strconv.FormatInt(d.c.Memory*2, 10)); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}