block: partition: convert percpu ref

Percpu refcount is the perfect match for partition's case,
and the conversion is quite straight.

With the convertion, one pair of atomic inc/dec can be saved
for accounting block I/O, which is run in hot path of block I/O.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/genhd.c b/block/genhd.c
index 85df45292dbaf97bc94e6bc7cd18380343c17928..0c706f33a599a723fc56b0ef87bb58a71de2cd66 100644 (file)
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1284,7 +1284,11 @@ struct gendisk *alloc_disk_node(int minors, int node_id)
                 * converted to make use of bd_mutex and sequence counters.
                 */
                seqcount_init(&disk->part0.nr_sects_seq);
-               hd_ref_init(&disk->part0);
+               if (hd_ref_init(&disk->part0)) {
+                       hd_free_part(&disk->part0);
+                       kfree(disk);
+                       return NULL;
+               }
 
                disk->minors = minors;
                rand_initialize_disk(disk);

diff --git a/block/partition-generic.c b/block/partition-generic.c
index eca0d02a607c2ab555f66c4bdd2de3701c3788f4..e7711133284e187dd4a0ed74a151b0880b342d33 100644 (file)
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -232,8 +232,9 @@ static void delete_partition_rcu_cb(struct rcu_head *head)
        put_device(part_to_dev(part));
 }
 
-void __delete_partition(struct hd_struct *part)
+void __delete_partition(struct percpu_ref *ref)
 {
+       struct hd_struct *part = container_of(ref, struct hd_struct, ref);
        call_rcu(&part->rcu_head, delete_partition_rcu_cb);
 }
 
@@ -254,7 +255,7 @@ void delete_partition(struct gendisk *disk, int partno)
        kobject_put(part->holder_dir);
        device_del(part_to_dev(part));
 
-       hd_struct_put(part);
+       hd_struct_kill(part);
 }
 
 static ssize_t whole_disk_show(struct device *dev,
@@ -355,8 +356,8 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
        if (!dev_get_uevent_suppress(ddev))
                kobject_uevent(&pdev->kobj, KOBJ_ADD);
 
-       hd_ref_init(p);
-       return p;
+       if (!hd_ref_init(p))
+               return p;
 
 out_free_info:
        free_part_info(p);

diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index a221220ffcb2dbf43b520f69056b9df76dcfb4f8..2adbfa6d02bc4b10ecee8af9c641f177d184157a 100644 (file)
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -13,6 +13,7 @@
 #include <linux/kdev_t.h>
 #include <linux/rcupdate.h>
 #include <linux/slab.h>
+#include <linux/percpu-refcount.h>
 
 #ifdef CONFIG_BLOCK
 
@@ -124,7 +125,7 @@ struct hd_struct {
 #else
        struct disk_stats dkstats;
 #endif
-       atomic_t ref;
+       struct percpu_ref ref;
        struct rcu_head rcu_head;
 };
 
@@ -611,7 +612,7 @@ extern struct hd_struct * __must_check add_partition(struct gendisk *disk,
                                                     sector_t len, int flags,
                                                     struct partition_meta_info
                                                       *info);
-extern void __delete_partition(struct hd_struct *);
+extern void __delete_partition(struct percpu_ref *);
 extern void delete_partition(struct gendisk *, int);
 extern void printk_all_partitions(void);
 
@@ -640,33 +641,39 @@ extern ssize_t part_fail_store(struct device *dev,
                               const char *buf, size_t count);
 #endif /* CONFIG_FAIL_MAKE_REQUEST */
 
-static inline void hd_ref_init(struct hd_struct *part)
+static inline int hd_ref_init(struct hd_struct *part)
 {
-       atomic_set(&part->ref, 1);
-       smp_mb();
+       if (percpu_ref_init(&part->ref, __delete_partition, 0,
+                               GFP_KERNEL))
+               return -ENOMEM;
+       return 0;
 }
 
 static inline void hd_struct_get(struct hd_struct *part)
 {
-       atomic_inc(&part->ref);
-       smp_mb__after_atomic();
+       percpu_ref_get(&part->ref);
 }
 
 static inline int hd_struct_try_get(struct hd_struct *part)
 {
-       return atomic_inc_not_zero(&part->ref);
+       return percpu_ref_tryget_live(&part->ref);
 }
 
 static inline void hd_struct_put(struct hd_struct *part)
 {
-       if (atomic_dec_and_test(&part->ref))
-               __delete_partition(part);
+       percpu_ref_put(&part->ref);
+}
+
+static inline void hd_struct_kill(struct hd_struct *part)
+{
+       percpu_ref_kill(&part->ref);
 }
 
 static inline void hd_free_part(struct hd_struct *part)
 {
        free_part_stats(part);
        free_part_info(part);
+       percpu_ref_exit(&part->ref);
 }
 
 /*