linux-kernel - Re: [PATCH v3 8/9] ext3: use memweight()

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Message-ID: <20120612091436.GD6021@quack.suse.cz>
Date:	Tue, 12 Jun 2012 11:14:36 +0200
From:	Jan Kara <jack@...e.cz>
To:	Akinobu Mita <akinobu.mita@...il.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Jan Kara <jack@...e.cz>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH v3 8/9] ext3: use memweight()

On Sat 09-06-12 09:50:37, Akinobu Mita wrote:
> Convert ext3_count_free() to use memweight() instead of table lookup
> based counting clear bits implementation.  This change only affects
> the code segments enabled by EXT3FS_DEBUG.
> 
> Note that this memweight() call can't be replaced with a single
> bitmap_weight() call, although the pointer to the memory area is
> aligned to long-word boundary.  Because the size of the memory area
> may not be a multiple of BITS_PER_LONG, then it returns wrong value on
> big-endian architecture.
> 
> This also includes the following changes.
> 
> - Remove unnecessary map == NULL check in ext3_count_free() which
>   always takes non-null pointer as the memory area.
> 
> - Fix printk format warning that only reveals with EXT3FS_DEBUG.
> 
> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> Cc: Jan Kara <jack@...e.cz>
  Acked-by: Jan Kara <jack@...e.cz>

								Honza

> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Andreas Dilger <adilger.kernel@...ger.ca>
> Cc: linux-ext4@...r.kernel.org
> ---
> v3: rewrite to keep ext3_count_free() as a wrapper for memweight()
> 
>  fs/ext3/balloc.c |    2 +-
>  fs/ext3/bitmap.c |   12 +-----------
>  2 files changed, 2 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/ext3/balloc.c b/fs/ext3/balloc.c
> index 25cd608..90d901f 100644
> --- a/fs/ext3/balloc.c
> +++ b/fs/ext3/balloc.c
> @@ -1813,7 +1813,7 @@ ext3_fsblk_t ext3_count_free_blocks(struct super_block *sb)
>  	brelse(bitmap_bh);
>  	printk("ext3_count_free_blocks: stored = "E3FSBLK
>  		", computed = "E3FSBLK", "E3FSBLK"\n",
> -	       le32_to_cpu(es->s_free_blocks_count),
> +	       (ext3_fsblk_t)le32_to_cpu(es->s_free_blocks_count),
>  		desc_count, bitmap_count);
>  	return bitmap_count;
>  #else
> diff --git a/fs/ext3/bitmap.c b/fs/ext3/bitmap.c
> index 909d13e..ef9c643 100644
> --- a/fs/ext3/bitmap.c
> +++ b/fs/ext3/bitmap.c
> @@ -11,19 +11,9 @@
>  
>  #ifdef EXT3FS_DEBUG
>  
> -static const int nibblemap[] = {4, 3, 3, 2, 3, 2, 2, 1, 3, 2, 2, 1, 2, 1, 1, 0};
> -
>  unsigned long ext3_count_free (struct buffer_head * map, unsigned int numchars)
>  {
> -	unsigned int i;
> -	unsigned long sum = 0;
> -
> -	if (!map)
> -		return (0);
> -	for (i = 0; i < numchars; i++)
> -		sum += nibblemap[map->b_data[i] & 0xf] +
> -			nibblemap[(map->b_data[i] >> 4) & 0xf];
> -	return (sum);
> +	return numchars * BITS_PER_BYTE - memweight(map->b_data, numchars);
>  }
>  
>  #endif  /*  EXT3FS_DEBUG  */
> -- 
> 1.7.7.6
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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