linux-ext4 - Re: [PATCH 1/2] Use ext4_ext_next_allocated_block instead of mext_next

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Date:	Thu, 14 Aug 2014 17:03:59 +0200 (CEST)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
cc:	linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH 1/2] Use ext4_ext_next_allocated_block instead of
 mext_next_extent

On Wed, 13 Aug 2014, Dmitry Monakhov wrote:

> Date: Wed, 13 Aug 2014 19:45:10 +0400
> From: Dmitry Monakhov <dmonakhov@...nvz.org>
> To: linux-ext4@...r.kernel.org
> Cc: tytso@....edu, Dmitry Monakhov <dmonakhov@...nvz.org>
> Subject: [PATCH 1/2] Use ext4_ext_next_allocated_block instead of
>     mext_next_extent
> 
> This allow to make mext_next_extent static.
> 
> Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
> ---
>  fs/ext4/ext4.h        |    2 --
>  fs/ext4/extents.c     |   18 ++++++------------
>  fs/ext4/move_extent.c |    2 +-
>  3 files changed, 7 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 5b19760..f8d85f7 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2739,8 +2739,6 @@ extern void ext4_double_up_write_data_sem(struct inode *orig_inode,
>  extern int ext4_move_extents(struct file *o_filp, struct file *d_filp,
>  			     __u64 start_orig, __u64 start_donor,
>  			     __u64 len, __u64 *moved_len);
> -extern int mext_next_extent(struct inode *inode, struct ext4_ext_path *path,
> -			    struct ext4_extent **extent);
>  
>  /* page-io.c */
>  extern int __init ext4_init_pageio(void);
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 76c2df3..2e38ecb 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -5304,7 +5304,7 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
>  	struct ext4_ext_path *path;
>  	int ret = 0, depth;
>  	struct ext4_extent *extent;
> -	ext4_lblk_t stop_block, current_block;
> +	ext4_lblk_t stop_block;
>  	ext4_lblk_t ex_start, ex_end;
>  
>  	/* Let path point to the last extent */
> @@ -5365,18 +5365,12 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
>  					 (unsigned long) start);
>  			return -EIO;
>  		}
> -
> -		current_block = le32_to_cpu(extent->ee_block);
> -		if (start > current_block) {
> +		if (start > le32_to_cpu(extent->ee_block)) {
>  			/* Hole, move to the next extent */
> -			ret = mext_next_extent(inode, path, &extent);
> -			if (ret != 0) {
> -				ext4_ext_drop_refs(path);
> -				kfree(path);
> -				if (ret == 1)
> -					ret = 0;
> -				break;
> -			}
> +			start = ext4_ext_next_allocated_block(path);
> +			ext4_ext_drop_refs(path);
> +			kfree(path);
> +			continue;

It seems to me that this will affect the performance of the shift as
we would potentially need to do more iteration, because the current
code would update the "extents" to the actual next extent and then
then do the shift right away, while your solution just finds the
next block and then jumps at the beginning of the loop to generate
path and find the extent all over again. What do you think ?

-Lukas

>  		}
>  		ret = ext4_ext_shift_path_extents(path, shift, inode,
>  				handle, &start);
> diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
> index 671a74b..123a51b 100644
> --- a/fs/ext4/move_extent.c
> +++ b/fs/ext4/move_extent.c
> @@ -76,7 +76,7 @@ copy_extent_status(struct ext4_extent *src, struct ext4_extent *dest)
>   * ext4_ext_path structure refers to the last extent, or a negative error
>   * value on failure.
>   */
> -int
> +static int
>  mext_next_extent(struct inode *inode, struct ext4_ext_path *path,
>  		      struct ext4_extent **extent)
>  {
> 
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