linux-ext4 - Re: [PATCH] ext2: start from parent blockgroup when trying linear search for a free inode

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Date:   Mon, 3 Jun 2019 12:05:45 +0200
From:   Jan Kara <jack@...e.cz>
To:     Chengguang Xu <cgxu519@...o.com.cn>
Cc:     jack@...e.com, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext2: start from parent blockgroup when trying linear
 search for a free inode

On Sat 01-06-19 16:49:41, Chengguang Xu wrote:
> Start from parent blockgroup when trying linear search
> for a free indoe because for non directory inode it's
> better to keep in same blockgroup with parent.
> 
> Signed-off-by: Chengguang Xu <cgxu519@...o.com.cn>

Thanks for the patch! As much as I agree that incrementing group before
calling ext2_get_group_desc() was probably an oversight I don't think that
changing that at this point is good. For ext2 driver we don't really care
about performance too much anymore and also existing filesystems have
inodes for files in a directory allocated in parent_group + 1 and this
change would spread them also to parent_group effectively worsening the
situation.

								Honza

> ---
>  fs/ext2/ialloc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext2/ialloc.c b/fs/ext2/ialloc.c
> index fda7d3f5b4be..435463a255e6 100644
> --- a/fs/ext2/ialloc.c
> +++ b/fs/ext2/ialloc.c
> @@ -411,11 +411,11 @@ static int find_group_other(struct super_block *sb, struct inode *parent)
>  	 */
>  	group = parent_group;
>  	for (i = 0; i < ngroups; i++) {
> -		if (++group >= ngroups)
> -			group = 0;
>  		desc = ext2_get_group_desc (sb, group, NULL);
>  		if (desc && le16_to_cpu(desc->bg_free_inodes_count))
>  			goto found;
> +		if (++group >= ngroups)
> +			group = 0;
>  	}
>  
>  	return -1;
> -- 
> 2.17.2
> 
> 
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR