linux-kernel - Re: [PATCH] ida: fix up bitmap size calculation

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Date:	Fri, 03 Sep 2010 11:14:04 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Namhyung Kim <namhyung@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ida: fix up bitmap size calculation

On 09/02/2010 08:07 PM, Namhyung Kim wrote:
> Namhyung Kim <namhyung@...il.com> writes:
>> Got it. :-) I'll prepare new patch with that comment, then.
>> Thank you for the explanation.
> 
> How about this?

I'd prefer something with a bit more brevity.  If this looks good, can
you please send it to trivial@...nel.org?

Thanks.

diff --git a/include/linux/idr.h b/include/linux/idr.h
index e968db7..1208528 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -117,9 +117,12 @@ 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 accomodate
+ * 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_LONGS	(IDA_CHUNK_SIZE / sizeof(long) - 1)
 #define IDA_BITMAP_BITS		(IDA_BITMAP_LONGS * sizeof(long) * 8)

 struct ida_bitmap {


-- 
tejun
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