Regulate filesystem driver to max of 100 calls

It's easily possible for a flood of requests to trigger thousands of
concurrent file accesses on the storage driver. Each file I/O call creates
a new OS thread that is not reaped by the Golang runtime. By limiting it
to only 100 at a time we can effectively bound the number of OS threads
in use by the storage driver.

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)

Signed-off-by: Tony Holdstock-Brown <tony@docker.com>

docs/storage/driver/filesystem/driver.go

@@ -60,12 +60,12 @@ func FromParameters(parameters map[string]interface{}) *Driver {
 
 // New constructs a new Driver with a given rootDirectory
 func New(rootDirectory string) *Driver {
+	fsDriver := &driver{rootDirectory: rootDirectory}
+
 	return &Driver{
 		baseEmbed: baseEmbed{
 			Base: base.Base{
-				StorageDriver: &driver{
-					rootDirectory: rootDirectory,
-				},
+				StorageDriver: base.NewRegulator(fsDriver, 100),
 			},
 		},
 	}