Commit be8981be authored by Lukas Czerner's avatar Lukas Czerner Committed by Theodore Ts'o
Browse files

ext4: try to prepend extent to the existing one 



Currently when inserting extent in ext4_ext_insert_extent() we would
only try to to see if we can append new extent to the found extent. If
we can not, then we proceed with adding new extent into the extent tree,
but then possibly merging it back again.

We can avoid this situation by trying to append and prepend new extent
to the existing ones. However since the new extent can be on either
sides of the existing extent, we have to pick the right extent to try to
append/prepend to.

This patch adds the conditions to pick the right extent to
append/prepend to and adds the actual prepending condition as well. This
will also eliminate the need to use "reserved" block for possibly
growing extent tree.

Signed-off-by: default avatarLukas Czerner <lczerner@redhat.com>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent bc2d9db4

fs/ext4/extents.c

+85 −23
Original line number Diff line number Diff line
@@ -1813,29 +1813,54 @@ int ext4_ext_insert_extent(handle_t *handle, struct inode *inode, 
	}

	depth = ext_depth(inode);

	ex = path[depth].p_ext;

	eh = path[depth].p_hdr;

	if (unlikely(path[depth].p_hdr == NULL)) {

		EXT4_ERROR_INODE(inode, "path[%d].p_hdr == NULL", depth);

		return -EIO;

	}



	/* try to insert block into found extent and return */

	if (ex && !(flag & EXT4_GET_BLOCKS_PRE_IO)

		&& ext4_can_extents_be_merged(inode, ex, newext)) {

		ext_debug("append [%d]%d block to %u:[%d]%d (from %llu)\n",

	if (ex && !(flag & EXT4_GET_BLOCKS_PRE_IO)) {



		/*

		 * Try to see whether we should rather test the extent on

		 * right from ex, or from the left of ex. This is because

		 * ext4_ext_find_extent() can return either extent on the

		 * left, or on the right from the searched position. This

		 * will make merging more effective.

		 */

		if (ex < EXT_LAST_EXTENT(eh) &&

		    (le32_to_cpu(ex->ee_block) +

		    ext4_ext_get_actual_len(ex) <

		    le32_to_cpu(newext->ee_block))) {

			ex += 1;

			goto prepend;

		} else if ((ex > EXT_FIRST_EXTENT(eh)) &&

			   (le32_to_cpu(newext->ee_block) +

			   ext4_ext_get_actual_len(newext) <

			   le32_to_cpu(ex->ee_block)))

			ex -= 1;



		/* Try to append newex to the ex */

		if (ext4_can_extents_be_merged(inode, ex, newext)) {

			ext_debug("append [%d]%d block to %u:[%d]%d"

				  "(from %llu)\n",

				  ext4_ext_is_uninitialized(newext),

				  ext4_ext_get_actual_len(newext),

				  le32_to_cpu(ex->ee_block),

				  ext4_ext_is_uninitialized(ex),

				  ext4_ext_get_actual_len(ex),

				  ext4_ext_pblock(ex));

		err = ext4_ext_get_access(handle, inode, path + depth);

			err = ext4_ext_get_access(handle, inode,

						  path + depth);

			if (err)

				return err;



			/*

		 * ext4_can_extents_be_merged should have checked that either

		 * both extents are uninitialized, or both aren't. Thus we

		 * need to check only one of them here.

			 * ext4_can_extents_be_merged should have checked

			 * that either both extents are uninitialized, or

			 * both aren't. Thus we need to check only one of

			 * them here.

			 */

			if (ext4_ext_is_uninitialized(ex))

				uninitialized = 1;
@@ -1848,6 +1873,43 @@ int ext4_ext_insert_extent(handle_t *handle, struct inode *inode, 
			goto merge;

		}



prepend:

		/* Try to prepend newex to the ex */

		if (ext4_can_extents_be_merged(inode, newext, ex)) {

			ext_debug("prepend %u[%d]%d block to %u:[%d]%d"

				  "(from %llu)\n",

				  le32_to_cpu(newext->ee_block),

				  ext4_ext_is_uninitialized(newext),

				  ext4_ext_get_actual_len(newext),

				  le32_to_cpu(ex->ee_block),

				  ext4_ext_is_uninitialized(ex),

				  ext4_ext_get_actual_len(ex),

				  ext4_ext_pblock(ex));

			err = ext4_ext_get_access(handle, inode,

						  path + depth);

			if (err)

				return err;



			/*

			 * ext4_can_extents_be_merged should have checked

			 * that either both extents are uninitialized, or

			 * both aren't. Thus we need to check only one of

			 * them here.

			 */

			if (ext4_ext_is_uninitialized(ex))

				uninitialized = 1;

			ex->ee_block = newext->ee_block;

			ext4_ext_store_pblock(ex, ext4_ext_pblock(newext));

			ex->ee_len = cpu_to_le16(ext4_ext_get_actual_len(ex)

					+ ext4_ext_get_actual_len(newext));

			if (uninitialized)

				ext4_ext_mark_uninitialized(ex);

			eh = path[depth].p_hdr;

			nearex = ex;

			goto merge;

		}

	}



	depth = ext_depth(inode);

	eh = path[depth].p_hdr;

	if (le16_to_cpu(eh->eh_entries) < le16_to_cpu(eh->eh_max))

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