block: always use a percpu variable for disk stats

percpu variables have a perfectly fine working stub implementation
for UP kernels, so use that.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk.h

@@ -378,7 +378,7 @@ static inline void hd_struct_put(struct hd_struct *part)
 
 static inline void hd_free_part(struct hd_struct *part)
 {
-	free_part_stats(part);
+	free_percpu(part->dkstats);
 	kfree(part->info);
 	percpu_ref_exit(&part->ref);
 }

block/genhd.c

@@ -92,7 +92,6 @@ const char *bdevname(struct block_device *bdev, char *buf)
 }
 EXPORT_SYMBOL(bdevname);
 
-#ifdef CONFIG_SMP
 static void part_stat_read_all(struct hd_struct *part, struct disk_stats *stat)
 {
 	int cpu;
@@ -112,12 +111,6 @@ static void part_stat_read_all(struct hd_struct *part, struct disk_stats *stat)
 		stat->io_ticks += ptr->io_ticks;
 	}
 }
-#else /* CONFIG_SMP */
-static void part_stat_read_all(struct hd_struct *part, struct disk_stats *stat)
-{
-	memcpy(stat, &part->dkstats, sizeof(struct disk_stats));
-}
-#endif /* CONFIG_SMP */
 
 static unsigned int part_in_flight(struct request_queue *q,
 		struct hd_struct *part)
@@ -1688,14 +1681,15 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
 
 	disk = kzalloc_node(sizeof(struct gendisk), GFP_KERNEL, node_id);
 	if (disk) {
-		if (!init_part_stats(&disk->part0)) {
+		disk->part0.dkstats = alloc_percpu(struct disk_stats);
+		if (!disk->part0.dkstats) {
 			kfree(disk);
 			return NULL;
 		}
 		init_rwsem(&disk->lookup_sem);
 		disk->node_id = node_id;
 		if (disk_expand_part_tbl(disk, 0)) {
-			free_part_stats(&disk->part0);
+			free_percpu(disk->part0.dkstats);
 			kfree(disk);
 			return NULL;
 		}

block/partitions/core.c

@@ -387,7 +387,8 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
 	if (!p)
 		return ERR_PTR(-EBUSY);
 
-	if (!init_part_stats(p)) {
+	p->dkstats = alloc_percpu(struct disk_stats);
+	if (!p->dkstats) {
 		err = -ENOMEM;
 		goto out_free;
 	}
@@ -468,7 +469,7 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
 out_free_info:
 	kfree(p->info);
 out_free_stats:
-	free_part_stats(p);
+	free_percpu(p->dkstats);
 out_free:
 	kfree(p);
 	return ERR_PTR(err);

include/linux/genhd.h

@@ -39,15 +39,6 @@ extern struct class block_class;
 #include <linux/fs.h>
 #include <linux/workqueue.h>
 
-struct disk_stats {
-	u64 nsecs[NR_STAT_GROUPS];
-	unsigned long sectors[NR_STAT_GROUPS];
-	unsigned long ios[NR_STAT_GROUPS];
-	unsigned long merges[NR_STAT_GROUPS];
-	unsigned long io_ticks;
-	local_t in_flight[2];
-};
-
 #define PARTITION_META_INFO_VOLNAMELTH	64
 /*
  * Enough for the string representation of any kind of UUID plus NULL.
@@ -72,11 +63,7 @@ struct hd_struct {
 	seqcount_t nr_sects_seq;
 #endif
 	unsigned long stamp;
-#ifdef	CONFIG_SMP
 	struct disk_stats __percpu *dkstats;
-#else
-	struct disk_stats dkstats;
-#endif
 	struct percpu_ref ref;
 
 	sector_t alignment_offset;

include/linux/part_stat.h

@@ -4,19 +4,23 @@
 
 #include <linux/genhd.h>
 
+struct disk_stats {
+	u64 nsecs[NR_STAT_GROUPS];
+	unsigned long sectors[NR_STAT_GROUPS];
+	unsigned long ios[NR_STAT_GROUPS];
+	unsigned long merges[NR_STAT_GROUPS];
+	unsigned long io_ticks;
+	local_t in_flight[2];
+};
+
 /*
  * Macros to operate on percpu disk statistics:
  *
- * {disk|part|all}_stat_{add|sub|inc|dec}() modify the stat counters
- * and should be called between disk_stat_lock() and
- * disk_stat_unlock().
+ * {disk|part|all}_stat_{add|sub|inc|dec}() modify the stat counters and should
+ * be called between disk_stat_lock() and disk_stat_unlock().
  *
  * part_stat_read() can be called at any time.
- *
- * part_stat_{add|set_all}() and {init|free}_part_stats are for
- * internal use only.
  */
-#ifdef	CONFIG_SMP
 #define part_stat_lock()	({ rcu_read_lock(); get_cpu(); })
 #define part_stat_unlock()	do { put_cpu(); rcu_read_unlock(); } while (0)
 
@@ -44,43 +48,6 @@ static inline void part_stat_set_all(struct hd_struct *part, int value)
 				sizeof(struct disk_stats));
 }
 
-static inline int init_part_stats(struct hd_struct *part)
-{
-	part->dkstats = alloc_percpu(struct disk_stats);
-	if (!part->dkstats)
-		return 0;
-	return 1;
-}
-
-static inline void free_part_stats(struct hd_struct *part)
-{
-	free_percpu(part->dkstats);
-}
-
-#else /* !CONFIG_SMP */
-#define part_stat_lock()	({ rcu_read_lock(); 0; })
-#define part_stat_unlock()	rcu_read_unlock()
-
-#define part_stat_get(part, field)		((part)->dkstats.field)
-#define part_stat_get_cpu(part, field, cpu)	part_stat_get(part, field)
-#define part_stat_read(part, field)		part_stat_get(part, field)
-
-static inline void part_stat_set_all(struct hd_struct *part, int value)
-{
-	memset(&part->dkstats, value, sizeof(struct disk_stats));
-}
-
-static inline int init_part_stats(struct hd_struct *part)
-{
-	return 1;
-}
-
-static inline void free_part_stats(struct hd_struct *part)
-{
-}
-
-#endif /* CONFIG_SMP */
-
 #define part_stat_read_accum(part, field)				\
 	(part_stat_read(part, field[STAT_READ]) +			\
 	 part_stat_read(part, field[STAT_WRITE]) +			\