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Commit 8c854473 authored by Dmitry Monakhov's avatar Dmitry Monakhov Committed by Theodore Ts'o
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ext4: reimplement uninit extent optimization for move_extent_per_page() 



Uninitialized extent may became initialized(parallel writeback task)
at any moment after we drop i_data_sem, so we have to recheck extent's
state after we hold page's lock and i_data_sem.

If we about to change page's mapping we must hold page's lock in order to
serialize other users.

Signed-off-by: default avatarDmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent bb557488

fs/ext4/move_extent.c

+76 −5
Original line number Diff line number Diff line
@@ -594,6 +594,43 @@ mext_calc_swap_extents(struct ext4_extent *tmp_dext, 
	return 0;

}



/**

 * mext_check_coverage - Check that all extents in range has the same type

 *

 * @inode:		inode in question

 * @from:		block offset of inode

 * @count:		block count to be checked

 * @uninit:		extents expected to be uninitialized

 * @err:		pointer to save error value

 *

 * Return 1 if all extents in range has expected type, and zero otherwise.

 */

static int

mext_check_coverage(struct inode *inode, ext4_lblk_t from, ext4_lblk_t count,

			  int uninit, int *err)

{

	struct ext4_ext_path *path = NULL;

	struct ext4_extent *ext;

	ext4_lblk_t last = from + count;

	while (from < last) {

		*err = get_ext_path(inode, from, &path);

		if (*err)

			return 0;

		ext = path[ext_depth(inode)].p_ext;

		if (!ext) {

			ext4_ext_drop_refs(path);

			return 0;

		}

		if (uninit != ext4_ext_is_uninitialized(ext)) {

			ext4_ext_drop_refs(path);

			return 0;

		}

		from += ext4_ext_get_actual_len(ext);

		ext4_ext_drop_refs(path);

	}

	return 1;

}



/**

 * mext_replace_branches - Replace original extents with new extents

 *
@@ -629,9 +666,6 @@ mext_replace_branches(handle_t *handle, struct inode *orig_inode, 
	int replaced_count = 0;

	int dext_alen;



	/* Protect extent trees against block allocations via delalloc */

	double_down_write_data_sem(orig_inode, donor_inode);



	/* Get the original extent for the block "orig_off" */

	*err = get_ext_path(orig_inode, orig_off, &orig_path);

	if (*err)
@@ -730,8 +764,6 @@ mext_replace_branches(handle_t *handle, struct inode *orig_inode, 
	ext4_ext_invalidate_cache(orig_inode);

	ext4_ext_invalidate_cache(donor_inode);



	double_up_write_data_sem(orig_inode, donor_inode);



	return replaced_count;

}
@@ -925,7 +957,46 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode, 
				     pagep);

	if (unlikely(*err < 0))

		goto stop_journal;

	/*

	 * If orig extent was uninitialized it can become initialized

	 * at any time after i_data_sem was dropped, in order to

	 * serialize with delalloc we have recheck extent while we

	 * hold page's lock, if it is still the case data copy is not

	 * necessary, just swap data blocks between orig and donor.

	 */

	if (uninit) {

		double_down_write_data_sem(orig_inode, donor_inode);

		/* If any of extents in range became initialized we have to

		 * fallback to data copying */

		uninit = mext_check_coverage(orig_inode, orig_blk_offset,

					     block_len_in_page, 1, err);

		if (*err)

			goto drop_data_sem;



		uninit &= mext_check_coverage(donor_inode, orig_blk_offset,

					      block_len_in_page, 1, err);

		if (*err)

			goto drop_data_sem;



		if (!uninit) {

			double_up_write_data_sem(orig_inode, donor_inode);

			goto data_copy;

		}

		if ((page_has_private(pagep[0]) &&

		     !try_to_release_page(pagep[0], 0)) ||

		    (page_has_private(pagep[1]) &&

		     !try_to_release_page(pagep[1], 0))) {

			*err = -EBUSY;

			goto drop_data_sem;

		}

		replaced_count = mext_replace_branches(handle, orig_inode,

						donor_inode, orig_blk_offset,

						block_len_in_page, err);

	drop_data_sem:

		double_up_write_data_sem(orig_inode, donor_inode);

		goto unlock_pages;

	}

data_copy:

	*err = mext_page_mkuptodate(pagep[0], from, from + replaced_size);

	if (*err)

		goto unlock_pages;