linux-kernel - [PATCH 4/4] idr: reorder the fields

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Date:	Tue, 22 Apr 2014 18:16:21 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	<linux-kernel@...r.kernel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Jeff Layton <jlayton@...hat.com>,
	Andreas Gruenbacher <agruen@...bit.com>,
	Stephen Hemminger <stephen@...workplumber.org>
Subject: [PATCH 4/4] 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@...fujitsu.com>
---
 include/linux/idr.h |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/include/linux/idr.h b/include/linux/idr.h
index 3a77b33..c537c55 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)							\
-- 
1.7.4.4

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