linux-kernel - [PATCH] ida: document IDA_BITMAP

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Date:	Fri,  3 Sep 2010 18:38:18 +0900
From:	Namhyung Kim <namhyung@...il.com>
To:	trivial@...nel.org
Cc:	tj@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] ida: document IDA_BITMAP_LONGS calculation

IDA_BITMAP_LONGS value is calculated take into account struct ida_bitmap
not to waste memory space. Comment it.

Signed-off-by: Namhyung Kim <namhyung@...il.com>
Acked-by: Tejun Heo <tj@...nel.org>
---
 include/linux/idr.h |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/include/linux/idr.h b/include/linux/idr.h
index e968db7..3f4b718 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -117,10 +117,13 @@ void idr_init(struct idr *idp);
 /*
  * IDA - IDR based id allocator, use when translation from id to
  * pointer isn't necessary.
+ *
+ * IDA_BITMAP_LONGS is calculated to be one less to accommodate
+ * ida_bitmap->nr_busy so that the whole struct fits in 128 bytes.
  */
 #define IDA_CHUNK_SIZE		128	/* 128 bytes per chunk */
 #define IDA_BITMAP_LONGS	(128 / sizeof(long) - 1)
-#define IDA_BITMAP_BITS		(IDA_BITMAP_LONGS * sizeof(long) * 8)
+#define IDA_BITMAP_BITS 	(IDA_BITMAP_LONGS * sizeof(long) * 8)
 
 struct ida_bitmap {
 	long			nr_busy;
-- 
1.7.2.2

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