linux-kernel - Re: [PATCH v2 10/10] ext4: use memweight()

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Message-Id: <B6D8D29B-9D9E-4248-B1EE-703D46354522@dilger.ca>
Date:	Sat, 2 Jun 2012 08:35:23 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Akinobu Mita <akinobu.mita@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Akinobu Mita <akinobu.mita@...il.com>,
	"Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2 10/10] ext4: use memweight()

On 2012-06-02, at 7:40, Akinobu Mita <akinobu.mita@...il.com> wrote:

> Use memweight() to count the total number of bits clear in memory area.
> This change only affects the code segments enabled by EXT4FS_DEBUG.

Personally, I'd rather still keep a thin wrapper ext4_count_free() and put the memweight() call and math inside that. The function name ext4_count_free() is meaningful to readers, while memweight() is much less so. 

Cheers, Andreas

> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> Cc: "Theodore Ts'o" <tytso@....edu>
> Cc: Andreas Dilger <adilger.kernel@...ger.ca>
> Cc: linux-ext4@...r.kernel.org
> ---
> 
> v2: don't remove bitmap.c which now has other than ext4_count_free()
> 
> fs/ext4/balloc.c |    3 ++-
> fs/ext4/bitmap.c |   18 ------------------
> fs/ext4/ext4.h   |    1 -
> fs/ext4/ialloc.c |    4 +++-
> 4 files changed, 5 insertions(+), 21 deletions(-)
> 
> diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
> index 99b6324..e5eadfe 100644
> --- a/fs/ext4/balloc.c
> +++ b/fs/ext4/balloc.c
> @@ -609,7 +609,8 @@ ext4_fsblk_t ext4_count_free_clusters(struct super_block *sb)
>        if (bitmap_bh == NULL)
>            continue;
> 
> -        x = ext4_count_free(bitmap_bh, sb->s_blocksize);
> +        x = sb->s_blocksize * BITS_PER_BYTE -
> +            memweight(bitmap_bh->b_data, sb->s_blocksize);
>        printk(KERN_DEBUG "group %u: stored = %d, counted = %u\n",
>            i, ext4_free_group_clusters(sb, gdp), x);
>        bitmap_count += x;
> diff --git a/fs/ext4/bitmap.c b/fs/ext4/bitmap.c
> index b319721..3c67c97 100644
> --- a/fs/ext4/bitmap.c
> +++ b/fs/ext4/bitmap.c
> @@ -11,24 +11,6 @@
> #include <linux/jbd2.h>
> #include "ext4.h"
> 
> -#ifdef EXT4FS_DEBUG
> -
> -static const int nibblemap[] = {4, 3, 3, 2, 3, 2, 2, 1, 3, 2, 2, 1, 2, 1, 1, 0};
> -
> -unsigned int ext4_count_free(struct buffer_head *map, unsigned int numchars)
> -{
> -    unsigned int i, 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;
> -}
> -
> -#endif  /*  EXT4FS_DEBUG  */
> -
> int ext4_inode_bitmap_csum_verify(struct super_block *sb, ext4_group_t group,
>                  struct ext4_group_desc *gdp,
>                  struct buffer_head *bh, int sz)
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index cfc4e01..3a3511d 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1852,7 +1852,6 @@ struct mmpd_data {
> # define NORET_AND    noreturn,
> 
> /* bitmap.c */
> -extern unsigned int ext4_count_free(struct buffer_head *, unsigned);
> void ext4_inode_bitmap_csum_set(struct super_block *sb, ext4_group_t group,
>                struct ext4_group_desc *gdp,
>                struct buffer_head *bh, int sz);
> diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
> index d48e8b1..1310108 100644
> --- a/fs/ext4/ialloc.c
> +++ b/fs/ext4/ialloc.c
> @@ -1054,7 +1054,9 @@ unsigned long ext4_count_free_inodes(struct super_block *sb)
>        if (!bitmap_bh)
>            continue;
> 
> -        x = ext4_count_free(bitmap_bh, EXT4_INODES_PER_GROUP(sb) / 8);
> +        x = EXT4_INODES_PER_GROUP(sb) / 8 * BITS_PER_BYTE -
> +            memweight(bitmap_bh->b_data,
> +                EXT4_INODES_PER_GROUP(sb) / 8);
>        printk(KERN_DEBUG "group %lu: stored = %d, counted = %lu\n",
>            (unsigned long) i, ext4_free_inodes_count(sb, gdp), x);
>        bitmap_count += x;
> -- 
> 1.7.7.6
> 
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