[PATCH] Make I/O schedulers optional

Add kconfig options to allow excluding either or both the I/O
schedulers.  This can be useful for embedded systems (saves about ~13KB).

All schedulers are enabled by default for non-embedded.

drivers/block/Kconfig.iosched

+config IOSCHED_AS
+	bool "Anticipatory I/O scheduler" if EMBEDDED
+	default y
+
+config IOSCHED_DEADLINE
+	bool "Deadline I/O scheduler" if EMBEDDED
+	default y
+

drivers/block/Makefile

@@ -13,9 +13,10 @@
 # kblockd threads
 #
 
-obj-y	:= elevator.o ll_rw_blk.o ioctl.o genhd.o scsi_ioctl.o \
-	deadline-iosched.o as-iosched.o
+obj-y	:= elevator.o ll_rw_blk.o ioctl.o genhd.o scsi_ioctl.o
 
+obj-$(CONFIG_IOSCHED_AS)	+= as-iosched.o
+obj-$(CONFIG_IOSCHED_DEADLINE)	+= deadline-iosched.o
 obj-$(CONFIG_MAC_FLOPPY)	+= swim3.o
 obj-$(CONFIG_BLK_DEV_FD)	+= floppy.o
 obj-$(CONFIG_BLK_DEV_FD98)	+= floppy98.o

drivers/block/as-iosched.c

@@ -1842,6 +1842,7 @@ elevator_t iosched_as = {
 	.elevator_exit_fn =		as_exit,
 
 	.elevator_ktype =		&as_ktype,
+	.elevator_name =		"anticipatory scheduling",
 };
 
 EXPORT_SYMBOL(iosched_as);

drivers/block/deadline-iosched.c

@@ -940,6 +940,7 @@ elevator_t iosched_deadline = {
 	.elevator_exit_fn =		deadline_exit,
 
 	.elevator_ktype =		&deadline_ktype,
+	.elevator_name =		"deadline",
 };
 
 EXPORT_SYMBOL(iosched_deadline);

drivers/block/elevator.c

@@ -420,6 +420,7 @@ elevator_t elevator_noop = {
 	.elevator_merge_req_fn		= elevator_noop_merge_requests,
 	.elevator_next_req_fn		= elevator_noop_next_request,
 	.elevator_add_req_fn		= elevator_noop_add_request,
+	.elevator_name			= "noop",
 };
 
 module_init(elevator_global_init);

drivers/block/ll_rw_blk.c

@@ -1209,17 +1209,31 @@ static int blk_init_free_list(request_queue_t *q)
 
 static int __make_request(request_queue_t *, struct bio *);
 
-static elevator_t *chosen_elevator = &iosched_as;
-
+static elevator_t *chosen_elevator =
+#if defined(CONFIG_IOSCHED_AS)
+	&iosched_as;
+#elif defined(CONFIG_IOSCHED_DEADLINE)
+	&iosched_deadline;
+#else
+	&elevator_noop;
+#endif
+
+#if defined(CONFIG_IOSCHED_AS) || defined(CONFIG_IOSCHED_DEADLINE)
 static int __init elevator_setup(char *str)
 {
+#ifdef CONFIG_IOSCHED_DEADLINE
 	if (!strcmp(str, "deadline"))
 		chosen_elevator = &iosched_deadline;
+#endif
+#ifdef CONFIG_IOSCHED_AS
 	if (!strcmp(str, "as"))
 		chosen_elevator = &iosched_as;
+#endif
 	return 1;
 }
+
 __setup("elevator=", elevator_setup);
+#endif /* CONFIG_IOSCHED_AS || CONFIG_IOSCHED_DEADLINE */
 
 /**
  * blk_init_queue  - prepare a request queue for use with a block device
@@ -1259,10 +1273,7 @@ int blk_init_queue(request_queue_t *q, request_fn_proc *rfn, spinlock_t *lock)
 
 	if (!printed) {
 		printed = 1;
-		if (chosen_elevator == &iosched_deadline)
-			printk("deadline elevator\n");
-		else if (chosen_elevator == &iosched_as)
-			printk("anticipatory scheduling elevator\n");
+		printk("Using %s elevator\n", chosen_elevator->elevator_name);
 	}
 
 	if ((ret = elevator_init(q, chosen_elevator))) {

include/linux/elevator.h

@@ -54,6 +54,7 @@ struct elevator_s
 
 	struct kobject kobj;
 	struct kobj_type *elevator_ktype;
+	const char *elevator_name;
 };
 
 /*

init/Kconfig

@@ -141,6 +141,8 @@ config EPOLL
 	  Disabling this option will cause the kernel to be built without
 	  support for epoll family of system calls.
 
+source "drivers/block/Kconfig.iosched"
+
 endmenu		# General setup