ext4: use ext4_da_writepages() for all modes

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@mit.edu>

fs/ext4/inode.c

@@ -1799,7 +1799,7 @@ static int __ext4_journalled_writepage(struct page *page,
 * 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 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
	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 @@ static int ext4_da_writepages(struct address_space *mapping,
		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,

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),