devmapper: Add option for specifying the thin pool blocksize

Add dm.blocksize option that you can use with --storage-opt to set a
specific blocksize for the thin provisioning pool.

Also change the default dm-thin-pool blocksize from 64K to 512K.  This
strikes a balance between the desire to have smaller blocksize given
docker's use of snapshots versus the desire to have more performance
that comes with using a larger blocksize.  But if very small files will
be used on average the user is encouraged to override this default.

Docker-DCO-1.1-Signed-off-by: Mike Snitzer <snitzer@redhat.com> (github: snitm)

daemon/graphdriver/devmapper/README.md

@@ -126,6 +126,14 @@ Here is the list of supported options:
 
     ``docker -d --storage-opt dm.datadev=/dev/sdb1 --storage-opt dm.metadatadev=/dev/sdc1``
 
+ *  `dm.blocksize`
+
+    Specifies a custom blocksize to use for the thin pool.
+
+    Example use:
+
+    ``docker -d --storage-opt dm.blocksize=64K``
+
  *  `dm.blkdiscard`
 
     Enables or disables the use of blkdiscard when removing

daemon/graphdriver/devmapper/deviceset.go

@@ -28,6 +28,7 @@ var (
 	DefaultDataLoopbackSize     int64  = 100 * 1024 * 1024 * 1024
 	DefaultMetaDataLoopbackSize int64  = 2 * 1024 * 1024 * 1024
 	DefaultBaseFsSize           uint64 = 10 * 1024 * 1024 * 1024
+	DefaultThinpBlockSize       uint32  = 1024 // 512K = 1024 512b sectors
 )
 
 type DevInfo struct {
@@ -78,6 +79,7 @@ type DeviceSet struct {
 	dataDevice           string
 	metadataDevice       string
 	doBlkDiscard         bool
+	thinpBlockSize       uint32
 }
 
 type DiskUsage struct {
@@ -510,7 +512,7 @@ func (devices *DeviceSet) ResizePool(size int64) error {
 	}
 
 	// Reload with the new block sizes
-	if err := reloadPool(devices.getPoolName(), dataloopback, metadataloopback); err != nil {
+	if err := reloadPool(devices.getPoolName(), dataloopback, metadataloopback, devices.thinpBlockSize); err != nil {
 		return fmt.Errorf("Unable to reload pool: %s", err)
 	}
 
@@ -640,7 +642,7 @@ func (devices *DeviceSet) initDevmapper(doInit bool) error {
 		}
 		defer metadataFile.Close()
 
-		if err := createPool(devices.getPoolName(), dataFile, metadataFile); err != nil {
+		if err := createPool(devices.getPoolName(), dataFile, metadataFile, devices.thinpBlockSize); err != nil {
 			return err
 		}
 	}
@@ -1159,6 +1161,7 @@ func NewDeviceSet(root string, doInit bool, options []string) (*DeviceSet, error
 		baseFsSize:           DefaultBaseFsSize,
 		filesystem:           "ext4",
 		doBlkDiscard:         true,
+		thinpBlockSize:       DefaultThinpBlockSize,
 	}
 
 	foundBlkDiscard := false
@@ -1206,6 +1209,13 @@ func NewDeviceSet(root string, doInit bool, options []string) (*DeviceSet, error
 			if err != nil {
 				return nil, err
 			}
+		case "dm.blocksize":
+			size, err := units.RAMInBytes(val)
+			if err != nil {
+				return nil, err
+			}
+			// convert to 512b sectors
+			devices.thinpBlockSize = uint32(size) >> 9
 		default:
 			return nil, fmt.Errorf("Unknown option %s\n", key)
 		}

daemon/graphdriver/devmapper/devmapper.go

@@ -328,7 +328,7 @@ func BlockDeviceDiscard(path string) error {
 }
 
 // This is the programmatic example of "dmsetup create"
-func createPool(poolName string, dataFile, metadataFile *os.File) error {
+func createPool(poolName string, dataFile, metadataFile *os.File, poolBlockSize uint32) error {
 	task, err := createTask(DeviceCreate, poolName)
 	if task == nil {
 		return err
@@ -339,7 +339,7 @@ func createPool(poolName string, dataFile, metadataFile *os.File) error {
 		return fmt.Errorf("Can't get data size %s", err)
 	}
 
-	params := metadataFile.Name() + " " + dataFile.Name() + " 128 32768 1 skip_block_zeroing"
+	params := fmt.Sprintf("%s %s %d 32768 1 skip_block_zeroing", metadataFile.Name(), dataFile.Name(), poolBlockSize)
 	if err := task.AddTarget(0, size/512, "thin-pool", params); err != nil {
 		return fmt.Errorf("Can't add target %s", err)
 	}
@@ -358,7 +358,7 @@ func createPool(poolName string, dataFile, metadataFile *os.File) error {
 	return nil
 }
 
-func reloadPool(poolName string, dataFile, metadataFile *os.File) error {
+func reloadPool(poolName string, dataFile, metadataFile *os.File, poolBlockSize uint32) error {
 	task, err := createTask(DeviceReload, poolName)
 	if task == nil {
 		return err
@@ -369,7 +369,7 @@ func reloadPool(poolName string, dataFile, metadataFile *os.File) error {
 		return fmt.Errorf("Can't get data size %s", err)
 	}
 
-	params := metadataFile.Name() + " " + dataFile.Name() + " 128 32768 1 skip_block_zeroing"
+	params := fmt.Sprintf("%s %s %d 32768 1 skip_block_zeroing", metadataFile.Name(), dataFile.Name(), poolBlockSize)
 	if err := task.AddTarget(0, size/512, "thin-pool", params); err != nil {
 		return fmt.Errorf("Can't add target %s", err)
 	}