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Date:	Tue, 25 Jun 2013 15:30:21 +0200
From:	Jan Kara <jack@...e.cz>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: use ext4_da_writepages() for all modes

On Thu 06-06-13 14:01:16, Ted Tso wrote:
> Rename ext4_da_writepages() to ext4_writepages() and use it for all
> modes.  We still need to iterate over all the pages in the case of
> data=journalling, but in the case of nodelalloc/data=ordered (which is
> what file systems mounted using ext3 backwards compatibility will use)
> this will allow us to use a much more efficient I/O submission path.
> 
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
  Funny I was thinking about doing the same a few days ago :). Anyway, the
patch looks good. You can add:
  Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/inode.c             | 41 +++++++++++++++++++++++++++++++----------
>  include/trace/events/ext4.h |  4 ++--
>  2 files changed, 33 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 442c5d2..0db830d 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -1799,7 +1799,7 @@ out:
>   * lock so we have to do some magic.
>   *
>   * This function can get called via...
> - *   - ext4_da_writepages after taking page lock (have journal handle)
> + *   - ext4_writepages after taking page lock (have journal handle)
>   *   - journal_submit_inode_data_buffers (no journal handle)
>   *   - shrink_page_list via the kswapd/direct reclaim (no journal handle)
>   *   - grab_page_cache when doing write_begin (have journal handle)
> @@ -2217,7 +2217,7 @@ static int mpage_map_and_submit_extent(handle_t *handle,
>  
>  /*
>   * Calculate the total number of credits to reserve for one writepages
> - * iteration. This is called from ext4_da_writepages(). We map an extent of
> + * iteration. This is called from ext4_writepages(). We map an extent of
>   * upto MAX_WRITEPAGES_EXTENT_LEN blocks and then we go on and finish mapping
>   * the last partial page. So in total we can map MAX_WRITEPAGES_EXTENT_LEN +
>   * bpp - 1 blocks in bpp different extents.
> @@ -2349,8 +2349,17 @@ out:
>  	return err;
>  }
>  
> -static int ext4_da_writepages(struct address_space *mapping,
> -			      struct writeback_control *wbc)
> +static int __writepage(struct page *page, struct writeback_control *wbc,
> +		       void *data)
> +{
> +	struct address_space *mapping = data;
> +	int ret = ext4_writepage(page, wbc);
> +	mapping_set_error(mapping, ret);
> +	return ret;
> +}
> +
> +static int ext4_writepages(struct address_space *mapping,
> +			   struct writeback_control *wbc)
>  {
>  	pgoff_t	writeback_index = 0;
>  	long nr_to_write = wbc->nr_to_write;
> @@ -2364,7 +2373,7 @@ static int ext4_da_writepages(struct address_space *mapping,
>  	bool done;
>  	struct blk_plug plug;
>  
> -	trace_ext4_da_writepages(inode, wbc);
> +	trace_ext4_writepages(inode, wbc);
>  
>  	/*
>  	 * No pages to write? This is mainly a kludge to avoid starting
> @@ -2374,13 +2383,23 @@ static int ext4_da_writepages(struct address_space *mapping,
>  	if (!mapping->nrpages || !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
>  		return 0;
>  
> +	if (ext4_should_journal_data(inode)) {
> +		struct blk_plug plug;
> +		int ret;
> +
> +		blk_start_plug(&plug);
> +		ret = write_cache_pages(mapping, wbc, __writepage, mapping);
> +		blk_finish_plug(&plug);
> +		return ret;
> +	}
> +
>  	/*
>  	 * If the filesystem has aborted, it is read-only, so return
>  	 * right away instead of dumping stack traces later on that
>  	 * will obscure the real source of the problem.  We test
>  	 * EXT4_MF_FS_ABORTED instead of sb->s_flag's MS_RDONLY because
>  	 * the latter could be true if the filesystem is mounted
> -	 * read-only, and in that case, ext4_da_writepages should
> +	 * read-only, and in that case, ext4_writepages should
>  	 * *never* be called, so if that ever happens, we would want
>  	 * the stack trace.
>  	 */
> @@ -2520,8 +2539,8 @@ retry:
>  		mapping->writeback_index = mpd.first_page;
>  
>  out_writepages:
> -	trace_ext4_da_writepages_result(inode, wbc, ret,
> -					nr_to_write - wbc->nr_to_write);
> +	trace_ext4_writepages_result(inode, wbc, ret,
> +				     nr_to_write - wbc->nr_to_write);
>  	return ret;
>  }
>  
> @@ -2769,7 +2788,7 @@ int ext4_alloc_da_blocks(struct inode *inode)
>  	 * laptop_mode, not even desirable).  However, to do otherwise
>  	 * would require replicating code paths in:
>  	 *
> -	 * ext4_da_writepages() ->
> +	 * ext4_writepages() ->
>  	 *    write_cache_pages() ---> (via passed in callback function)
>  	 *        __mpage_da_writepage() -->
>  	 *           mpage_add_bh_to_extent()
> @@ -3213,6 +3232,7 @@ static const struct address_space_operations ext4_aops = {
>  	.readpage		= ext4_readpage,
>  	.readpages		= ext4_readpages,
>  	.writepage		= ext4_writepage,
> +	.writepages		= ext4_writepages,
>  	.write_begin		= ext4_write_begin,
>  	.write_end		= ext4_write_end,
>  	.bmap			= ext4_bmap,
> @@ -3228,6 +3248,7 @@ static const struct address_space_operations ext4_journalled_aops = {
>  	.readpage		= ext4_readpage,
>  	.readpages		= ext4_readpages,
>  	.writepage		= ext4_writepage,
> +	.writepages		= ext4_writepages,
>  	.write_begin		= ext4_write_begin,
>  	.write_end		= ext4_journalled_write_end,
>  	.set_page_dirty		= ext4_journalled_set_page_dirty,
> @@ -3243,7 +3264,7 @@ static const struct address_space_operations ext4_da_aops = {
>  	.readpage		= ext4_readpage,
>  	.readpages		= ext4_readpages,
>  	.writepage		= ext4_writepage,
> -	.writepages		= ext4_da_writepages,
> +	.writepages		= ext4_writepages,
>  	.write_begin		= ext4_da_write_begin,
>  	.write_end		= ext4_da_write_end,
>  	.bmap			= ext4_bmap,
> diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
> index 832a412..72f523e 100644
> --- a/include/trace/events/ext4.h
> +++ b/include/trace/events/ext4.h
> @@ -281,7 +281,7 @@ DEFINE_EVENT(ext4__write_end, ext4_da_write_end,
>  	TP_ARGS(inode, pos, len, copied)
>  );
>  
> -TRACE_EVENT(ext4_da_writepages,
> +TRACE_EVENT(ext4_writepages,
>  	TP_PROTO(struct inode *inode, struct writeback_control *wbc),
>  
>  	TP_ARGS(inode, wbc),
> @@ -379,7 +379,7 @@ TRACE_EVENT(ext4_da_write_pages_extent,
>  		  __entry->flags)
>  );
>  
> -TRACE_EVENT(ext4_da_writepages_result,
> +TRACE_EVENT(ext4_writepages_result,
>  	TP_PROTO(struct inode *inode, struct writeback_control *wbc,
>  			int ret, int pages_written),
>  
> -- 
> 1.7.12.rc0.22.gcdd159b
> 
> --
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-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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