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

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Message-ID: <20161114085419.GC2524@quack2.suse.cz>
Date:   Mon, 14 Nov 2016 09:54:19 +0100
From:   Jan Kara <jack@...e.cz>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 06/11] ext4: Avoid split extents for DAX writes

On Fri 11-11-16 13:25:47, Ross Zwisler wrote:
> 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?

Well, the previous patch just mostly moved the block allocation logic from
dedicated DAX get_block function into iomap_begin(). This patch changes the
block allocation logic so I prefer to keep them separate - mostly for the
sake of documenting the change how allocation of blocks for DAX works in the
changelog.

								Honza

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