Re: [PATCH] ext4: modify block allocation algorithm for the last group

[Mingming Cao <cmm@us.ibm.com>]

On Wed, 2008-02-13 at 17:26 +0100, Valerie Clement wrote:
> Modify the block allocation algorithm for the last group
> 
> From: Valerie Clement <valerie.clement@bull.net>
> 
> When a directory inode is allocated in the last group and the last group
> contains less than s_blocks_per_group blocks, the initial block allocated
> for the directory is not always allocated in the same group as the
> directory inode, but in one of the first groups of the filesystem (group 1
> for example).
> Depending on the current process's pid, ext4_find_near() and 
> ext4_ext_find_goal() can return a block number greater than the maximum
> blocks count in the filesystem and in that case the block will be not
> allocated in the same group as the inode.
> 
> The following patch fixes the problem.
> 
> Comments?
Looks sane to me. 

> Should the modification also be done in ext2/3 code?
> 
I think so.

Mingming
> Signed-off-by: Valerie Clement <valerie.clement@bull.net>
> ---
> 
>  fs/ext4/extents.c |    8 +++++++-
>  fs/ext4/inode.c   |    8 +++++++-
>  2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 5c4af51..1391ded 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -148,6 +148,7 @@ ext4_fsblk_t ext4_ext_find_goal(struct inode *inode,
>  {
>  	struct ext4_inode_info *ei = EXT4_I(inode);
>  	ext4_fsblk_t bg_start;
> +	ext4_fsblk_t last_block;
>  	ext4_grpblk_t colour;
>  	int depth;
> 
> @@ -169,8 +170,13 @@ ext4_fsblk_t ext4_ext_find_goal(struct inode *inode,
>  	/* OK. use inode's group */
>  	bg_start = (ei->i_block_group * EXT4_BLOCKS_PER_GROUP(inode->i_sb)) +
>  		le32_to_cpu(EXT4_SB(inode->i_sb)->s_es->s_first_data_block);
> -	colour = (current->pid % 16) *
> +	last_block = ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es) - 1;
> +
> +	if (bg_start + EXT4_BLOCKS_PER_GROUP(inode->i_sb) <= last_block)
> +		colour = (current->pid % 16) *
>  			(EXT4_BLOCKS_PER_GROUP(inode->i_sb) / 16);
> +	else
> +		colour = (current->pid % 16) * ((last_block - bg_start) / 16);
>  	return bg_start + colour + block;
>  }
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 51bf3b5..c4f8ace 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -405,6 +405,7 @@ static ext4_fsblk_t ext4_find_near(struct inode *inode, Indirect *ind)
>  	__le32 *start = ind->bh ? (__le32*) ind->bh->b_data : ei->i_data;
>  	__le32 *p;
>  	ext4_fsblk_t bg_start;
> +	ext4_fsblk_t last_block;
>  	ext4_grpblk_t colour;
> 
>  	/* Try to find previous block */
> @@ -422,8 +423,13 @@ static ext4_fsblk_t ext4_find_near(struct inode *inode, Indirect *ind)
>  	 * into the same cylinder group then.
>  	 */
>  	bg_start = ext4_group_first_block_no(inode->i_sb, ei->i_block_group);
> -	colour = (current->pid % 16) *
> +	last_block = ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es) - 1;
> +
> +	if (bg_start + EXT4_BLOCKS_PER_GROUP(inode->i_sb) <= last_block)
> +		colour = (current->pid % 16) *
>  			(EXT4_BLOCKS_PER_GROUP(inode->i_sb) / 16);
> +	else
> +		colour = (current->pid % 16) * ((last_block - bg_start) / 16);
>  	return bg_start + colour;
>  }
> 
> 
> 
> -
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