linux-kernel - Re: [PATCH v3 7/9] ext2: use memweight()

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Message-ID: <20120612091419.GC6021@quack.suse.cz>
Date:	Tue, 12 Jun 2012 11:14:19 +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>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v3 7/9] ext2: use memweight()

On Sat 09-06-12 09:50:36, Akinobu Mita wrote:
> Convert ext2_count_free() to use memweight() instead of table lookup
> based counting clear bits implementation.  This change only affects
> the code segments enabled by EXT2FS_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 ext2_count_free() which
>   always takes non-null pointer as the memory area.
> 
> - Fix printk format warning that only reveals with EXT2FS_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: linux-ext4@...r.kernel.org
> ---
> v3: rewrite to keep ext2_count_free() as a wrapper for memweight()
> 
>  fs/ext2/balloc.c |   14 ++------------
>  fs/ext2/ialloc.c |    1 +
>  2 files changed, 3 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
> index 1c36139..376aa77 100644
> --- a/fs/ext2/balloc.c
> +++ b/fs/ext2/balloc.c
> @@ -1444,19 +1444,9 @@ ext2_fsblk_t ext2_new_block(struct inode *inode, unsigned long goal, int *errp)
>  
>  #ifdef EXT2FS_DEBUG
>  
> -static const int nibblemap[] = {4, 3, 3, 2, 3, 2, 2, 1, 3, 2, 2, 1, 2, 1, 1, 0};
> -
> -unsigned long ext2_count_free (struct buffer_head * map, unsigned int numchars)
> +unsigned long ext2_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  /*  EXT2FS_DEBUG  */
> diff --git a/fs/ext2/ialloc.c b/fs/ext2/ialloc.c
> index c13eb7b..8f370e01 100644
> --- a/fs/ext2/ialloc.c
> +++ b/fs/ext2/ialloc.c
> @@ -644,6 +644,7 @@ unsigned long ext2_count_free_inodes (struct super_block * sb)
>  	}
>  	brelse(bitmap_bh);
>  	printk("ext2_count_free_inodes: stored = %lu, computed = %lu, %lu\n",
> +		(unsigned long)
>  		percpu_counter_read(&EXT2_SB(sb)->s_freeinodes_counter),
>  		desc_count, bitmap_count);
>  	return desc_count;
> -- 
> 1.7.7.6
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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