ext4: Add delayed allocation support in data=writeback mode

Updated with fixes from Mingming Cao <cmm@us.ibm.com> to unlock and
release the page from page cache if the delalloc write_begin failed, and
properly handle preallocated blocks.  Also added a fix to clear
buffer_delay in block_write_full_page() after allocating a delayed
buffer.

Updated with fixes from Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
to update i_disksize properly and to add bmap support for delayed
allocation.

Updated with a fix from Valerie Clement <valerie.clement@bull.net> to
avoid filesystem corruption when the filesystem is mounted with the
delalloc option and blocksize < pagesize.

Signed-off-by: Alex Tomas <alex@clusterfs.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by:  Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

fs/ext4/ext4.h

@@ -536,6 +536,7 @@ do {									       \
 #define EXT4_MOUNT_JOURNAL_ASYNC_COMMIT	0x1000000 /* Journal Async Commit */
 #define EXT4_MOUNT_I_VERSION            0x2000000 /* i_version support */
 #define EXT4_MOUNT_MBALLOC		0x4000000 /* Buddy allocation support */
+#define EXT4_MOUNT_DELALLOC		0x8000000 /* Delalloc support */
 /* Compatibility, for having both ext2_fs.h and ext4_fs.h included at once */
 #ifndef _LINUX_EXT2_FS_H
 #define clear_opt(o, opt)		o &= ~EXT4_MOUNT_##opt

fs/ext4/inode.c

@@ -32,6 +32,7 @@
 #include <linux/string.h>
 #include <linux/buffer_head.h>
 #include <linux/writeback.h>
+#include <linux/pagevec.h>
 #include <linux/mpage.h>
 #include <linux/uio.h>
 #include <linux/bio.h>
@@ -46,6 +47,8 @@ static inline int ext4_begin_ordered_truncate(struct inode *inode,
 						   new_size);
 }
 
+static void ext4_invalidatepage(struct page *page, unsigned long offset);
+
 /*
  * Test whether an inode is a fast symlink.
  */
@@ -1407,6 +1410,669 @@ static int ext4_journalled_write_end(struct file *file,
 	return ret ? ret : copied;
 }
 
+/*
+ * Delayed allocation stuff
+ */
+
+struct mpage_da_data {
+	struct inode *inode;
+	struct buffer_head lbh;			/* extent of blocks */
+	unsigned long first_page, next_page;	/* extent of pages */
+	get_block_t *get_block;
+	struct writeback_control *wbc;
+};
+
+/*
+ * mpage_da_submit_io - walks through extent of pages and try to write
+ * them with __mpage_writepage()
+ *
+ * @mpd->inode: inode
+ * @mpd->first_page: first page of the extent
+ * @mpd->next_page: page after the last page of the extent
+ * @mpd->get_block: the filesystem's block mapper function
+ *
+ * By the time mpage_da_submit_io() is called we expect all blocks
+ * to be allocated. this may be wrong if allocation failed.
+ *
+ * As pages are already locked by write_cache_pages(), we can't use it
+ */
+static int mpage_da_submit_io(struct mpage_da_data *mpd)
+{
+	struct address_space *mapping = mpd->inode->i_mapping;
+	struct mpage_data mpd_pp = {
+		.bio = NULL,
+		.last_block_in_bio = 0,
+		.get_block = mpd->get_block,
+		.use_writepage = 1,
+	};
+	int ret = 0, err, nr_pages, i;
+	unsigned long index, end;
+	struct pagevec pvec;
+
+	BUG_ON(mpd->next_page <= mpd->first_page);
+
+	pagevec_init(&pvec, 0);
+	index = mpd->first_page;
+	end = mpd->next_page - 1;
+
+	while (index <= end) {
+		/* XXX: optimize tail */
+		nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
+		if (nr_pages == 0)
+			break;
+		for (i = 0; i < nr_pages; i++) {
+			struct page *page = pvec.pages[i];
+
+			index = page->index;
+			if (index > end)
+				break;
+			index++;
+
+			err = __mpage_writepage(page, mpd->wbc, &mpd_pp);
+
+			/*
+			 * In error case, we have to continue because
+			 * remaining pages are still locked
+			 * XXX: unlock and re-dirty them?
+			 */
+			if (ret == 0)
+				ret = err;
+		}
+		pagevec_release(&pvec);
+	}
+	if (mpd_pp.bio)
+		mpage_bio_submit(WRITE, mpd_pp.bio);
+
+	return ret;
+}
+
+/*
+ * mpage_put_bnr_to_bhs - walk blocks and assign them actual numbers
+ *
+ * @mpd->inode - inode to walk through
+ * @exbh->b_blocknr - first block on a disk
+ * @exbh->b_size - amount of space in bytes
+ * @logical - first logical block to start assignment with
+ *
+ * the function goes through all passed space and put actual disk
+ * block numbers into buffer heads, dropping BH_Delay
+ */
+static void mpage_put_bnr_to_bhs(struct mpage_da_data *mpd, sector_t logical,
+				 struct buffer_head *exbh)
+{
+	struct inode *inode = mpd->inode;
+	struct address_space *mapping = inode->i_mapping;
+	int blocks = exbh->b_size >> inode->i_blkbits;
+	sector_t pblock = exbh->b_blocknr, cur_logical;
+	struct buffer_head *head, *bh;
+	unsigned long index, end;
+	struct pagevec pvec;
+	int nr_pages, i;
+
+	index = logical >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
+	end = (logical + blocks - 1) >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
+	cur_logical = index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
+
+	pagevec_init(&pvec, 0);
+
+	while (index <= end) {
+		/* XXX: optimize tail */
+		nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
+		if (nr_pages == 0)
+			break;
+		for (i = 0; i < nr_pages; i++) {
+			struct page *page = pvec.pages[i];
+
+			index = page->index;
+			if (index > end)
+				break;
+			index++;
+
+			BUG_ON(!PageLocked(page));
+			BUG_ON(PageWriteback(page));
+			BUG_ON(!page_has_buffers(page));
+
+			bh = page_buffers(page);
+			head = bh;
+
+			/* skip blocks out of the range */
+			do {
+				if (cur_logical >= logical)
+					break;
+				cur_logical++;
+			} while ((bh = bh->b_this_page) != head);
+
+			do {
+				if (cur_logical >= logical + blocks)
+					break;
+
+				if (buffer_delay(bh)) {
+					bh->b_blocknr = pblock;
+					clear_buffer_delay(bh);
+				} else if (buffer_mapped(bh)) {
+					BUG_ON(bh->b_blocknr != pblock);
+				}
+
+				cur_logical++;
+				pblock++;
+			} while ((bh = bh->b_this_page) != head);
+		}
+		pagevec_release(&pvec);
+	}
+}
+
+
+/*
+ * __unmap_underlying_blocks - just a helper function to unmap
+ * set of blocks described by @bh
+ */
+static inline void __unmap_underlying_blocks(struct inode *inode,
+					     struct buffer_head *bh)
+{
+	struct block_device *bdev = inode->i_sb->s_bdev;
+	int blocks, i;
+
+	blocks = bh->b_size >> inode->i_blkbits;
+	for (i = 0; i < blocks; i++)
+		unmap_underlying_metadata(bdev, bh->b_blocknr + i);
+}
+
+/*
+ * mpage_da_map_blocks - go through given space
+ *
+ * @mpd->lbh - bh describing space
+ * @mpd->get_block - the filesystem's block mapper function
+ *
+ * The function skips space we know is already mapped to disk blocks.
+ *
+ * The function ignores errors ->get_block() returns, thus real
+ * error handling is postponed to __mpage_writepage()
+ */
+static void mpage_da_map_blocks(struct mpage_da_data *mpd)
+{
+	struct buffer_head *lbh = &mpd->lbh;
+	int err = 0, remain = lbh->b_size;
+	sector_t next = lbh->b_blocknr;
+	struct buffer_head new;
+
+	/*
+	 * We consider only non-mapped and non-allocated blocks
+	 */
+	if (buffer_mapped(lbh) && !buffer_delay(lbh))
+		return;
+
+	while (remain) {
+		new.b_state = lbh->b_state;
+		new.b_blocknr = 0;
+		new.b_size = remain;
+		err = mpd->get_block(mpd->inode, next, &new, 1);
+		if (err) {
+			/*
+			 * Rather than implement own error handling
+			 * here, we just leave remaining blocks
+			 * unallocated and try again with ->writepage()
+			 */
+			break;
+		}
+		BUG_ON(new.b_size == 0);
+
+		if (buffer_new(&new))
+			__unmap_underlying_blocks(mpd->inode, &new);
+
+		/*
+		 * If blocks are delayed marked, we need to
+		 * put actual blocknr and drop delayed bit
+		 */
+		if (buffer_delay(lbh))
+			mpage_put_bnr_to_bhs(mpd, next, &new);
+
+			/* go for the remaining blocks */
+			next += new.b_size >> mpd->inode->i_blkbits;
+			remain -= new.b_size;
+		}
+}
+
+#define BH_FLAGS ((1 << BH_Uptodate) | (1 << BH_Mapped) | (1 << BH_Delay))
+
+/*
+ * mpage_add_bh_to_extent - try to add one more block to extent of blocks
+ *
+ * @mpd->lbh - extent of blocks
+ * @logical - logical number of the block in the file
+ * @bh - bh of the block (used to access block's state)
+ *
+ * the function is used to collect contig. blocks in same state
+ */
+static void mpage_add_bh_to_extent(struct mpage_da_data *mpd,
+				   sector_t logical, struct buffer_head *bh)
+{
+	struct buffer_head *lbh = &mpd->lbh;
+	sector_t next;
+
+	next = lbh->b_blocknr + (lbh->b_size >> mpd->inode->i_blkbits);
+
+	/*
+	 * First block in the extent
+	 */
+	if (lbh->b_size == 0) {
+		lbh->b_blocknr = logical;
+		lbh->b_size = bh->b_size;
+		lbh->b_state = bh->b_state & BH_FLAGS;
+		return;
+	}
+
+	/*
+	 * Can we merge the block to our big extent?
+	 */
+	if (logical == next && (bh->b_state & BH_FLAGS) == lbh->b_state) {
+		lbh->b_size += bh->b_size;
+		return;
+	}
+
+	/*
+	 * We couldn't merge the block to our extent, so we
+	 * need to flush current  extent and start new one
+	 */
+	mpage_da_map_blocks(mpd);
+
+	/*
+	 * Now start a new extent
+	 */
+	lbh->b_size = bh->b_size;
+	lbh->b_state = bh->b_state & BH_FLAGS;
+	lbh->b_blocknr = logical;
+}
+
+/*
+ * __mpage_da_writepage - finds extent of pages and blocks
+ *
+ * @page: page to consider
+ * @wbc: not used, we just follow rules
+ * @data: context
+ *
+ * The function finds extents of pages and scan them for all blocks.
+ */
+static int __mpage_da_writepage(struct page *page,
+				struct writeback_control *wbc, void *data)
+{
+	struct mpage_da_data *mpd = data;
+	struct inode *inode = mpd->inode;
+	struct buffer_head *bh, *head, fake;
+	sector_t logical;
+
+	/*
+	 * Can we merge this page to current extent?
+	 */
+	if (mpd->next_page != page->index) {
+		/*
+		 * Nope, we can't. So, we map non-allocated blocks
+		 * and start IO on them using __mpage_writepage()
+		 */
+		if (mpd->next_page != mpd->first_page) {
+			mpage_da_map_blocks(mpd);
+			mpage_da_submit_io(mpd);
+		}
+
+		/*
+		 * Start next extent of pages ...
+		 */
+		mpd->first_page = page->index;
+
+		/*
+		 * ... and blocks
+		 */
+		mpd->lbh.b_size = 0;
+		mpd->lbh.b_state = 0;
+		mpd->lbh.b_blocknr = 0;
+	}
+
+	mpd->next_page = page->index + 1;
+	logical = (sector_t) page->index <<
+		  (PAGE_CACHE_SHIFT - inode->i_blkbits);
+
+	if (!page_has_buffers(page)) {
+		/*
+		 * There is no attached buffer heads yet (mmap?)
+		 * we treat the page asfull of dirty blocks
+		 */
+		bh = &fake;
+		bh->b_size = PAGE_CACHE_SIZE;
+		bh->b_state = 0;
+		set_buffer_dirty(bh);
+		set_buffer_uptodate(bh);
+		mpage_add_bh_to_extent(mpd, logical, bh);
+	} else {
+		/*
+		 * Page with regular buffer heads, just add all dirty ones
+		 */
+		head = page_buffers(page);
+		bh = head;
+		do {
+			BUG_ON(buffer_locked(bh));
+			if (buffer_dirty(bh))
+				mpage_add_bh_to_extent(mpd, logical, bh);
+			logical++;
+		} while ((bh = bh->b_this_page) != head);
+	}
+
+	return 0;
+}
+
+/*
+ * mpage_da_writepages - walk the list of dirty pages of the given
+ * address space, allocates non-allocated blocks, maps newly-allocated
+ * blocks to existing bhs and issue IO them
+ *
+ * @mapping: address space structure to write
+ * @wbc: subtract the number of written pages from *@wbc->nr_to_write
+ * @get_block: the filesystem's block mapper function.
+ *
+ * This is a library function, which implements the writepages()
+ * address_space_operation.
+ *
+ * In order to avoid duplication of logic that deals with partial pages,
+ * multiple bio per page, etc, we find non-allocated blocks, allocate
+ * them with minimal calls to ->get_block() and re-use __mpage_writepage()
+ *
+ * It's important that we call __mpage_writepage() only once for each
+ * involved page, otherwise we'd have to implement more complicated logic
+ * to deal with pages w/o PG_lock or w/ PG_writeback and so on.
+ *
+ * See comments to mpage_writepages()
+ */
+static int mpage_da_writepages(struct address_space *mapping,
+			       struct writeback_control *wbc,
+			       get_block_t get_block)
+{
+	struct mpage_da_data mpd;
+	int ret;
+
+	if (!get_block)
+		return generic_writepages(mapping, wbc);
+
+	mpd.wbc = wbc;
+	mpd.inode = mapping->host;
+	mpd.lbh.b_size = 0;
+	mpd.lbh.b_state = 0;
+	mpd.lbh.b_blocknr = 0;
+	mpd.first_page = 0;
+	mpd.next_page = 0;
+	mpd.get_block = get_block;
+
+	ret = write_cache_pages(mapping, wbc, __mpage_da_writepage, &mpd);
+
+	/*
+	 * Handle last extent of pages
+	 */
+	if (mpd.next_page != mpd.first_page) {
+		mpage_da_map_blocks(&mpd);
+		mpage_da_submit_io(&mpd);
+	}
+
+	return ret;
+}
+
+/*
+ * this is a special callback for ->write_begin() only
+ * it's intention is to return mapped block or reserve space
+ */
+static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
+				  struct buffer_head *bh_result, int create)
+{
+	int ret = 0;
+
+	BUG_ON(create == 0);
+	BUG_ON(bh_result->b_size != inode->i_sb->s_blocksize);
+
+	/*
+	 * first, we need to know whether the block is allocated already
+	 * preallocated blocks are unmapped but should treated
+	 * the same as allocated blocks.
+	 */
+	ret = ext4_get_blocks_wrap(NULL, inode, iblock, 1,  bh_result, 0, 0);
+	if (ret == 0) {
+		/* the block isn't allocated yet, let's reserve space */
+		/* XXX: call reservation here */
+		/*
+		 * XXX: __block_prepare_write() unmaps passed block,
+		 * is it OK?
+		 */
+		map_bh(bh_result, inode->i_sb, 0);
+		set_buffer_new(bh_result);
+		set_buffer_delay(bh_result);
+	} else if (ret > 0) {
+		bh_result->b_size = (ret << inode->i_blkbits);
+		ret = 0;
+	}
+
+	return ret;
+}
+
+static int ext4_da_get_block_write(struct inode *inode, sector_t iblock,
+				   struct buffer_head *bh_result, int create)
+{
+	int ret, needed_blocks = ext4_writepage_trans_blocks(inode);
+	unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;
+	loff_t disksize = EXT4_I(inode)->i_disksize;
+	handle_t *handle = NULL;
+
+	if (create) {
+		handle = ext4_journal_start(inode, needed_blocks);
+		if (IS_ERR(handle)) {
+			ret = PTR_ERR(handle);
+			goto out;
+		}
+	}
+
+	ret = ext4_get_blocks_wrap(handle, inode, iblock, max_blocks,
+				   bh_result, create, 0);
+	if (ret > 0) {
+		bh_result->b_size = (ret << inode->i_blkbits);
+
+		/*
+		 * Update on-disk size along with block allocation
+		 * we don't use 'extend_disksize' as size may change
+		 * within already allocated block -bzzz
+		 */
+		disksize = ((loff_t) iblock + ret) << inode->i_blkbits;
+		if (disksize > i_size_read(inode))
+			disksize = i_size_read(inode);
+		if (disksize > EXT4_I(inode)->i_disksize) {
+			/*
+			 * XXX: replace with spinlock if seen contended -bzzz
+			 */
+			down_write(&EXT4_I(inode)->i_data_sem);
+			if (disksize > EXT4_I(inode)->i_disksize)
+				EXT4_I(inode)->i_disksize = disksize;
+			up_write(&EXT4_I(inode)->i_data_sem);
+
+			if (EXT4_I(inode)->i_disksize == disksize) {
+				if (handle == NULL)
+					handle = ext4_journal_start(inode, 1);
+				if (!IS_ERR(handle))
+					ext4_mark_inode_dirty(handle, inode);
+			}
+		}
+
+		ret = 0;
+	}
+
+out:
+	if (handle && !IS_ERR(handle))
+		ext4_journal_stop(handle);
+
+	return ret;
+}
+/* FIXME!! only support data=writeback mode */
+static int ext4_da_writepage(struct page *page,
+				struct writeback_control *wbc)
+{
+	struct inode *inode = page->mapping->host;
+	handle_t *handle = NULL;
+	int ret = 0;
+	int err;
+
+	if (ext4_journal_current_handle())
+		goto out_fail;
+
+	handle = ext4_journal_start(inode, ext4_writepage_trans_blocks(inode));
+	if (IS_ERR(handle)) {
+		ret = PTR_ERR(handle);
+		goto out_fail;
+	}
+
+	if (test_opt(inode->i_sb, NOBH) && ext4_should_writeback_data(inode))
+		ret = nobh_writepage(page, ext4_get_block, wbc);
+	else
+		ret = block_write_full_page(page, ext4_get_block, wbc);
+
+	if (!ret && inode->i_size > EXT4_I(inode)->i_disksize) {
+		EXT4_I(inode)->i_disksize = inode->i_size;
+		ext4_mark_inode_dirty(handle, inode);
+	}
+
+	err = ext4_journal_stop(handle);
+	if (!ret)
+		ret = err;
+	return ret;
+
+out_fail:
+	redirty_page_for_writepage(wbc, page);
+	unlock_page(page);
+	return ret;
+}
+
+static int ext4_da_writepages(struct address_space *mapping,
+				struct writeback_control *wbc)
+{
+	return mpage_da_writepages(mapping, wbc, ext4_da_get_block_write);
+}
+
+static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
+				loff_t pos, unsigned len, unsigned flags,
+				struct page **pagep, void **fsdata)
+{
+	int ret;
+	struct page *page;
+	pgoff_t index;
+	unsigned from, to;
+	struct inode *inode = mapping->host;
+	handle_t *handle;
+
+	index = pos >> PAGE_CACHE_SHIFT;
+	from = pos & (PAGE_CACHE_SIZE - 1);
+	to = from + len;
+
+	/*
+	 * With delayed allocation, we don't log the i_disksize update
+	 * if there is delayed block allocation. But we still need
+	 * to journalling the i_disksize update if writes to the end
+	 * of file which has an already mapped buffer.
+	 */
+	handle = ext4_journal_start(inode, 1);
+	if (IS_ERR(handle)) {
+		ret = PTR_ERR(handle);
+		goto out;
+	}
+
+	page = __grab_cache_page(mapping, index);
+	if (!page)
+		return -ENOMEM;
+	*pagep = page;
+
+	ret = block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
+							ext4_da_get_block_prep);
+	if (ret < 0) {
+		unlock_page(page);
+		ext4_journal_stop(handle);
+		page_cache_release(page);
+	}
+
+out:
+	return ret;
+}
+
+static int ext4_bh_unmapped_or_delay(handle_t *handle, struct buffer_head *bh)
+{
+	return !buffer_mapped(bh) || buffer_delay(bh);
+}
+
+static int ext4_da_write_end(struct file *file,
+				struct address_space *mapping,
+				loff_t pos, unsigned len, unsigned copied,
+				struct page *page, void *fsdata)
+{
+	struct inode *inode = mapping->host;
+	int ret = 0, ret2;
+	handle_t *handle = ext4_journal_current_handle();
+	loff_t new_i_size;
+
+	/*
+	 * generic_write_end() will run mark_inode_dirty() if i_size
+	 * changes.  So let's piggyback the i_disksize mark_inode_dirty
+	 * into that.
+	 */
+
+	new_i_size = pos + copied;
+	if (new_i_size > EXT4_I(inode)->i_disksize)
+		if (!walk_page_buffers(NULL, page_buffers(page),
+				       0, len, NULL, ext4_bh_unmapped_or_delay)){
+			/*
+			 * Updating i_disksize when extending file without
+			 * needing block allocation
+			 */
+			if (ext4_should_order_data(inode))
+				ret = ext4_jbd2_file_inode(handle, inode);
+
+			EXT4_I(inode)->i_disksize = new_i_size;
+		}
+	ret2 = generic_write_end(file, mapping, pos, len, copied,
+							page, fsdata);
+	copied = ret2;
+	if (ret2 < 0)
+		ret = ret2;
+	ret2 = ext4_journal_stop(handle);
+	if (!ret)
+		ret = ret2;
+
+	return ret ? ret : copied;
+}
+
+static void ext4_da_invalidatepage(struct page *page, unsigned long offset)
+{
+	struct buffer_head *head, *bh;
+	unsigned int curr_off = 0;
+
+	/*
+	 * Drop reserved blocks
+	 */
+	BUG_ON(!PageLocked(page));
+	if (!page_has_buffers(page))
+		goto out;
+
+	head = page_buffers(page);
+	bh = head;
+	do {
+		unsigned int next_off = curr_off + bh->b_size;
+
+		/*
+		 * is this block fully invalidated?
+		 */
+		if (offset <= curr_off && buffer_delay(bh)) {
+			clear_buffer_delay(bh);
+			/* XXX: add real stuff here */
+		}
+		curr_off = next_off;
+		bh = bh->b_this_page;
+	} while (bh != head);
+
+out:
+	ext4_invalidatepage(page, offset);
+
+	return;
+}
+
+
 /*
  * bmap() is special.  It gets used by applications such as lilo and by
  * the swapper to find the on-disk block of a specific piece of data.
@@ -1427,6 +2093,16 @@ static sector_t ext4_bmap(struct address_space *mapping, sector_t block)
 	journal_t *journal;
 	int err;
 
+	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
+			test_opt(inode->i_sb, DELALLOC)) {
+		/*
+		 * With delalloc we want to sync the file
+		 * so that we can make sure we allocate
+		 * blocks for file
+		 */
+		filemap_write_and_wait(mapping);
+	}
+
 	if (EXT4_I(inode)->i_state & EXT4_STATE_JDATA) {
 		/*
 		 * This is a REALLY heavyweight approach, but the use of
@@ -1471,11 +2147,6 @@ static int bput_one(handle_t *handle, struct buffer_head *bh)
 	return 0;
 }
 
-static int ext4_bh_unmapped_or_delay(handle_t *handle, struct buffer_head *bh)
-{
-	return !buffer_mapped(bh) || buffer_delay(bh);
-}
-
 /*
  * Note that we don't need to start a transaction unless we're journaling data
  * because we should have holes filled from ext4_page_mkwrite(). We even don't
@@ -1832,10 +2503,28 @@ static const struct address_space_operations ext4_journalled_aops = {
 	.releasepage	= ext4_releasepage,
 };
 
+static const struct address_space_operations ext4_da_aops = {
+	.readpage	= ext4_readpage,
+	.readpages	= ext4_readpages,
+	.writepage	= ext4_da_writepage,
+	.writepages	= ext4_da_writepages,
+	.sync_page	= block_sync_page,
+	.write_begin	= ext4_da_write_begin,
+	.write_end	= ext4_da_write_end,
+	.bmap		= ext4_bmap,
+	.invalidatepage	= ext4_da_invalidatepage,
+	.releasepage	= ext4_releasepage,
+	.direct_IO	= ext4_direct_IO,
+	.migratepage	= buffer_migrate_page,
+};
+
 void ext4_set_aops(struct inode *inode)
 {
 	if (ext4_should_order_data(inode))
 		inode->i_mapping->a_ops = &ext4_ordered_aops;
+	else if (ext4_should_writeback_data(inode) &&
+		 test_opt(inode->i_sb, DELALLOC))
+		inode->i_mapping->a_ops = &ext4_da_aops;
 	else if (ext4_should_writeback_data(inode))
 		inode->i_mapping->a_ops = &ext4_writeback_aops;
 	else

fs/ext4/super.c

@@ -898,7 +898,7 @@ enum {
 	Opt_jqfmt_vfsold, Opt_jqfmt_vfsv0, Opt_quota, Opt_noquota,
 	Opt_ignore, Opt_barrier, Opt_err, Opt_resize, Opt_usrquota,
 	Opt_grpquota, Opt_extents, Opt_noextents, Opt_i_version,
-	Opt_mballoc, Opt_nomballoc, Opt_stripe,
+	Opt_mballoc, Opt_nomballoc, Opt_stripe, Opt_delalloc,
 };
 
 static match_table_t tokens = {
@@ -957,6 +957,7 @@ static match_table_t tokens = {
 	{Opt_nomballoc, "nomballoc"},
 	{Opt_stripe, "stripe=%u"},
 	{Opt_resize, "resize"},
+	{Opt_delalloc, "delalloc"},
 	{Opt_err, NULL},
 };
 
@@ -1335,6 +1336,9 @@ static int parse_options (char *options, struct super_block *sb,
 				return 0;
 			sbi->s_stripe = option;
 			break;
+		case Opt_delalloc:
+			set_opt(sbi->s_mount_opt, DELALLOC);
+			break;
 		default:
 			printk (KERN_ERR
 				"EXT4-fs: Unrecognized mount option \"%s\" "