idr: reorder the fields

idr_layer->layer is always accessed in read path, move it in the front.

idr_layer->bitmap is moved on the bottom.  And rcu_head shares with
bitmap due to they do not be accessed at the same time.

idr->id_free/id_free_cnt/lock are free list fields, and moved to the
bottom.  They will be removed in near future.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 5 deletions

diff --git a/include/linux/idr.h b/include/linux/idr.h
index 6af3400b9b2f..013fd9bc4cb6 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -29,21 +29,24 @@
 
 struct idr_layer {
         int                     prefix; /* the ID prefix of this idr_layer */
-        DECLARE_BITMAP(bitmap, IDR_SIZE); /* A zero bit means "space here" */
+        int                     layer;  /* distance from leaf */
         struct idr_layer __rcu  *ary[1<<IDR_BITS];
         int                     count;  /* When zero, we can release it */
-        int                     layer;  /* distance from leaf */
-        struct rcu_head         rcu_head;
+        union {
+                /* A zero bit means "space here" */
+                DECLARE_BITMAP(bitmap, IDR_SIZE);
+                struct rcu_head         rcu_head;
+        };
 };
 
 struct idr {
         struct idr_layer __rcu  *hint;  /* the last layer allocated from */
         struct idr_layer __rcu  *top;
-        struct idr_layer        *id_free;
         int                     layers; /* only valid w/o concurrent changes */
-        int                     id_free_cnt;
         int                     cur;    /* current pos for cyclic allocation */
         spinlock_t              lock;
+        int                     id_free_cnt;
+        struct idr_layer        *id_free;
 };
 
 #define IDR_INIT(name)                                                  \