Set max readahead to a large value when mounting.

For #10.

mounted_file_system.go

@@ -154,6 +154,26 @@ func (c *MountConfig) bazilfuseOptions() (opts []bazilfuse.MountOption) {
 		opts = append(opts, bazilfuse.SetOption("noappledouble", ""))
 	}
 
+	// Ask the Linux kernel for larger read requests.
+	//
+	// As of 2015-03-26, the behavior in the kernel is:
+	//
+	//  *  (http://goo.gl/bQ1f1i, http://goo.gl/HwBrR6) Set the local variable
+	//     ra_pages to be init_response->max_readahead divided by the page size.
+	//
+	//  *  (http://goo.gl/gcIsSh, http://goo.gl/LKV2vA) Set
+	//     backing_dev_info::ra_pages to the min of that value and what was sent
+	//     in the request's max_readahead field.
+	//
+	//  *  (http://goo.gl/u2SqzH) Use backing_dev_info::ra_pages when deciding
+	//     how much to read ahead.
+	//
+	//  *  (http://goo.gl/JnhbdL) Don't read ahead at all if that field is zero.
+	//
+	// Reading a page at a time is a drag. Ask for a larger size.
+	const maxReadahead = 1 << 20
+	opts = append(opts, bazilfuse.MaxReadahead(maxReadahead))
+
 	// Last but not least: other user-supplied options.
 	for k, v := range c.Options {
 		opts = append(opts, bazilfuse.SetOption(k, v))