block: re-organize fields of 'struct hd_part'

Put all fields accessed in IO path together at the beginning
of the struct, so that all can be fetched in single cacheline.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@infradead.org>
Cc: Yufen Yu <yuyufen@huawei.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hou Tao <houtao1@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/genhd.h

@@ -71,6 +71,14 @@ struct hd_struct {
 #if BITS_PER_LONG==32 && defined(CONFIG_SMP)
 	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;
 	unsigned int discard_alignment;
 	struct device __dev;
@@ -80,13 +88,6 @@ struct hd_struct {
 #ifdef CONFIG_FAIL_MAKE_REQUEST
 	int make_it_fail;
 #endif
-	unsigned long stamp;
-#ifdef	CONFIG_SMP
-	struct disk_stats __percpu *dkstats;
-#else
-	struct disk_stats dkstats;
-#endif
-	struct percpu_ref ref;
 	struct rcu_work rcu_work;
 };