linux-kernel - Re: [PATCH RESEND 1/2] ida: document IDA_BITMAP

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Date:	Wed, 15 Sep 2010 08:22:17 -0700
From:	Randy Dunlap <rdunlap@...otime.net>
To:	Namhyung Kim <namhyung@...il.com>
Cc:	Jiri Kosina <trivial@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND 1/2] ida: document IDA_BITMAP_LONGS calculation

On Wed, 15 Sep 2010 21:46:01 +0900 Namhyung Kim wrote:

> 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)

Might as well do:

#define IDA_BITMAP_LONGS	(IDA_CHUNK_SIZE / sizeof(long) - 1)

instead of repeating the 128.


> -#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;
> -- 


---
~Randy
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