linux-ext4 - Re: [PATCH 06/11] ext4: Avoid split extents for DAX writes

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Date:   Fri, 11 Nov 2016 13:25:47 -0700
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [PATCH 06/11] ext4: Avoid split extents for DAX writes

On Tue, Nov 08, 2016 at 12:08:12PM +0100, Jan Kara wrote:
> Currently mapping of blocks for DAX writes happen with
> EXT4_GET_BLOCKS_PRE_IO flag set. That has a result that each
> ext4_map_blocks() call creates a separate written extent, although it
> could be merged to the neighboring extents in the extent tree.  The
> reason for using this flag is that in case the extent is unwritten, we
> need to convert it to written one and zero it out. However this "convert
> mapped range to written" operation is already implemented by
> ext4_map_blocks() for the case of data writes into unwritten extent. So
> just use flags for that mode of operation, simplify the code, and avoid
> unnecessary split extents.
> 
> Signed-off-by: Jan Kara <jack@...e.cz>

The code that this patch modifies was just introduced in the previous patch.
Is there a reason to keep both patches, or would it be cleaner just to squash
them and have one patch that introduces the code as you intend for it to end
up?

> ---
>  fs/ext4/inode.c | 17 -----------------
>  1 file changed, 17 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index a7079cab645a..3192ec0768d4 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3351,7 +3351,6 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  			return PTR_ERR(handle);
>  
>  		ret = ext4_map_blocks(handle, inode, &map,
> -				      EXT4_GET_BLOCKS_PRE_IO |
>  				      EXT4_GET_BLOCKS_CREATE_ZERO);
>  		if (ret < 0) {
>  			ext4_journal_stop(handle);
> @@ -3360,22 +3359,6 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  				goto retry;
>  			return ret;
>  		}
> -		/* For DAX writes we need to zero out unwritten extents */
> -		if (map.m_flags & EXT4_MAP_UNWRITTEN) {
> -			/*
> -			 * We are protected by i_mmap_sem or i_rwsem so we know
> -			 * block cannot go away from under us even though we
> -			 * dropped i_data_sem. Convert extent to written and
> -			 * write zeros there.
> -			 */
> -			ret = ext4_map_blocks(handle, inode, &map,
> -					      EXT4_GET_BLOCKS_CONVERT |
> -					      EXT4_GET_BLOCKS_CREATE_ZERO);
> -			if (ret < 0) {
> -				ext4_journal_stop(handle);
> -				return ret;
> -			}
> -		}
>  
>  		/*
>  		 * If we added blocks beyond i_size we need to make sure they
> -- 
> 2.6.6
> 
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