Re: [PATCH 33/53] ext4: use on-stack dentries in ext4_fc_replay_link_internal()

[Jan Kara <jack@suse.cz>]

On Fri 13-03-26 08:12:20, NeilBrown wrote:
> From: NeilBrown <neil@brown.name>
> 
> ext4_fc_replay_link_internal() uses two dentries to simply code-reuse
> when replaying a "link" operation.  It does not need to interact with
> the dcache and removes the dentries shortly after adding them.
> 
> They are passed to __ext4_link() which only performs read accesses on
> these dentries and only uses the name and parent of dentry_inode (plus
> checking a flag is unset) and only uses the inode of the parent.
> 
> So instead of allocating dentries and adding them to the dcache, allocat
> two dentries on the stack, set up the required fields, and pass these to
> __ext4_link().
> 
> This substantially simplifies the code and removes on of the few uses of
> d_alloc() - preparing for its removal.
> 
> Signed-off-by: NeilBrown <neil@brown.name>

Looks good to me. Feel free to add:

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

								Honza

> ---
>  fs/ext4/fast_commit.c | 40 ++++++++--------------------------------
>  1 file changed, 8 insertions(+), 32 deletions(-)
> 
> diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
> index 2a5daf1d9667..e3593bb90a62 100644
> --- a/fs/ext4/fast_commit.c
> +++ b/fs/ext4/fast_commit.c
> @@ -1446,8 +1446,6 @@ static int ext4_fc_replay_link_internal(struct super_block *sb,
>  				struct inode *inode)
>  {
>  	struct inode *dir = NULL;
> -	struct dentry *dentry_dir = NULL, *dentry_inode = NULL;
> -	struct qstr qstr_dname = QSTR_INIT(darg->dname, darg->dname_len);
>  	int ret = 0;
>  
>  	dir = ext4_iget(sb, darg->parent_ino, EXT4_IGET_NORMAL);
> @@ -1457,28 +1455,14 @@ static int ext4_fc_replay_link_internal(struct super_block *sb,
>  		goto out;
>  	}
>  
> -	dentry_dir = d_obtain_alias(dir);
> -	if (IS_ERR(dentry_dir)) {
> -		ext4_debug("Failed to obtain dentry");
> -		dentry_dir = NULL;
> -		goto out;
> -	}
> +	{
> +		struct dentry dentry_dir = { .d_inode = dir };
> +		const struct dentry dentry_inode = {
> +			.d_parent = &dentry_dir,
> +			.d_name = QSTR_LEN(darg->dname, darg->dname_len),
> +		};
>  
> -	dentry_inode = d_alloc(dentry_dir, &qstr_dname);
> -	if (!dentry_inode) {
> -		ext4_debug("Inode dentry not created.");
> -		ret = -ENOMEM;
> -		goto out;
> -	}
> -
> -	ihold(inode);
> -	inc_nlink(inode);
> -	ret = __ext4_link(dir, inode, dentry_inode);
> -	if (ret) {
> -		drop_nlink(inode);
> -		iput(inode);
> -	} else {
> -		d_instantiate(dentry_inode, inode);
> +		ret = __ext4_link(dir, inode, &dentry_inode);
>  	}
>  	/*
>  	 * It's possible that link already existed since data blocks
> @@ -1493,16 +1477,8 @@ static int ext4_fc_replay_link_internal(struct super_block *sb,
>  
>  	ret = 0;
>  out:
> -	if (dentry_dir) {
> -		d_drop(dentry_dir);
> -		dput(dentry_dir);
> -	} else if (dir) {
> +	if (dir)
>  		iput(dir);
> -	}
> -	if (dentry_inode) {
> -		d_drop(dentry_inode);
> -		dput(dentry_inode);
> -	}
>  
>  	return ret;
>  }
> -- 
> 2.50.0.107.gf914562f5916.dirty
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR