Re: [PATCH v3 3/4] ext2: perform dax_device lookup at mount

[Jan Kara <jack@suse.cz>]

On Wed 30-08-17 12:44:03, Dan Williams wrote:
> The ->iomap_begin() operation is a hot path, so cache the
> fs_dax_get_by_host() result at mount time to avoid the incurring the
> hash lookup overhead on a per-i/o basis.
> 
> Cc: "Theodore Ts'o" <tytso@mit.edu>
> Cc: Andreas Dilger <adilger.kernel@dilger.ca>
> Cc: Jan Kara <jack@suse.cz>
> Reported-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Looks good to me (and it looks even cleaner than your previous approach).
Just one nit below. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

> diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> index 7b1bc9059863..d9dd999568c2 100644
> --- a/fs/ext2/super.c
> +++ b/fs/ext2/super.c
> @@ -144,6 +144,7 @@ static void ext2_put_super (struct super_block * sb)
>  	int db_count;
>  	int i;
>  	struct ext2_sb_info *sbi = EXT2_SB(sb);
> +	struct dax_device *dax_dev = sbi->s_daxdev;
>  
>  	ext2_quota_off_umount(sb);
>  
> @@ -172,6 +173,7 @@ static void ext2_put_super (struct super_block * sb)
>  	sb->s_fs_info = NULL;
>  	kfree(sbi->s_blockgroup_lock);
>  	kfree(sbi);
> +	fs_put_dax(dax_dev);

The local variable looks superfluous here. I'd just do
	fs_put_dax(sbi->s_daxdev);

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR