Commit 749269fa authored by Amit Arora's avatar Amit Arora Committed by Theodore Ts'o
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Change on-disk format to support 2^15 uninitialized extents 



This change was suggested by Andreas Dilger. 
This patch changes the EXT_MAX_LEN value and extent code which marks/checks
uninitialized extents. With this change it will be possible to have
initialized extents with 2^15 blocks (earlier the max blocks we could have
was 2^15 - 1). This way we can have better extent-to-block alignment.
Now, maximum number of blocks we can have in an initialized extent is 2^15
and in an uninitialized extent is 2^15 - 1.

Signed-off-by: default avatarAmit Arora <aarora@in.ibm.com>
parent 56055d3a

fs/ext4/extents.c

+25 −3
Original line number Diff line number Diff line
@@ -1107,7 +1107,7 @@ static int 
ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,

				struct ext4_extent *ex2)

{

	unsigned short ext1_ee_len, ext2_ee_len;

	unsigned short ext1_ee_len, ext2_ee_len, max_len;



	/*

	 * Make sure that either both extents are uninitialized, or
@@ -1116,6 +1116,11 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1, 
	if (ext4_ext_is_uninitialized(ex1) ^ ext4_ext_is_uninitialized(ex2))

		return 0;



	if (ext4_ext_is_uninitialized(ex1))

		max_len = EXT_UNINIT_MAX_LEN;

	else

		max_len = EXT_INIT_MAX_LEN;



	ext1_ee_len = ext4_ext_get_actual_len(ex1);

	ext2_ee_len = ext4_ext_get_actual_len(ex2);
@@ -1128,7 +1133,7 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1, 
	 * as an RO_COMPAT feature, refuse to merge to extents if

	 * this can result in the top bit of ee_len being set.

	 */

	if (ext1_ee_len + ext2_ee_len > EXT_MAX_LEN)

	if (ext1_ee_len + ext2_ee_len > max_len)

		return 0;

#ifdef AGGRESSIVE_TEST

	if (le16_to_cpu(ex1->ee_len) >= 4)
@@ -1815,7 +1820,11 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode, 


		ex->ee_block = cpu_to_le32(block);

		ex->ee_len = cpu_to_le16(num);

		if (uninitialized)

		/*

		 * Do not mark uninitialized if all the blocks in the

		 * extent have been removed.

		 */

		if (uninitialized && num)

			ext4_ext_mark_uninitialized(ex);



		err = ext4_ext_dirty(handle, inode, path + depth);
@@ -2308,6 +2317,19 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode, 
	/* allocate new block */

	goal = ext4_ext_find_goal(inode, path, iblock);



	/*

	 * See if request is beyond maximum number of blocks we can have in

	 * a single extent. For an initialized extent this limit is

	 * EXT_INIT_MAX_LEN and for an uninitialized extent this limit is

	 * EXT_UNINIT_MAX_LEN.

	 */

	if (max_blocks > EXT_INIT_MAX_LEN &&

	    create != EXT4_CREATE_UNINITIALIZED_EXT)

		max_blocks = EXT_INIT_MAX_LEN;

	else if (max_blocks > EXT_UNINIT_MAX_LEN &&

		 create == EXT4_CREATE_UNINITIALIZED_EXT)

		max_blocks = EXT_UNINIT_MAX_LEN;



	/* Check if we can really insert (iblock)::(iblock+max_blocks) extent */

	newex.ee_block = cpu_to_le32(iblock);

	newex.ee_len = cpu_to_le16(max_blocks);

include/linux/ext4_fs_extents.h

+27 −4
Original line number Diff line number Diff line
@@ -141,7 +141,25 @@ typedef int (*ext_prepare_callback)(struct inode *, struct ext4_ext_path *, 


#define EXT_MAX_BLOCK	0xffffffff



#define EXT_MAX_LEN	((1UL << 15) - 1)

/*

 * EXT_INIT_MAX_LEN is the maximum number of blocks we can have in an

 * initialized extent. This is 2^15 and not (2^16 - 1), since we use the

 * MSB of ee_len field in the extent datastructure to signify if this

 * particular extent is an initialized extent or an uninitialized (i.e.

 * preallocated).

 * EXT_UNINIT_MAX_LEN is the maximum number of blocks we can have in an

 * uninitialized extent.

 * If ee_len is <= 0x8000, it is an initialized extent. Otherwise, it is an

 * uninitialized one. In other words, if MSB of ee_len is set, it is an

 * uninitialized extent with only one special scenario when ee_len = 0x8000.

 * In this case we can not have an uninitialized extent of zero length and

 * thus we make it as a special case of initialized extent with 0x8000 length.

 * This way we get better extent-to-group alignment for initialized extents.

 * Hence, the maximum number of blocks we can have in an *initialized*

 * extent is 2^15 (32768) and in an *uninitialized* extent is 2^15-1 (32767).

 */

#define EXT_INIT_MAX_LEN	(1UL << 15)

#define EXT_UNINIT_MAX_LEN	(EXT_INIT_MAX_LEN - 1)





#define EXT_FIRST_EXTENT(__hdr__) \
@@ -190,17 +208,22 @@ ext4_ext_invalidate_cache(struct inode *inode) 


static inline void ext4_ext_mark_uninitialized(struct ext4_extent *ext)

{

	ext->ee_len |= cpu_to_le16(0x8000);

	/* We can not have an uninitialized extent of zero length! */

	BUG_ON((le16_to_cpu(ext->ee_len) & ~EXT_INIT_MAX_LEN) == 0);

	ext->ee_len |= cpu_to_le16(EXT_INIT_MAX_LEN);

}



static inline int ext4_ext_is_uninitialized(struct ext4_extent *ext)

{

	return (int)(le16_to_cpu((ext)->ee_len) & 0x8000);

	/* Extent with ee_len of 0x8000 is treated as an initialized extent */

	return (le16_to_cpu(ext->ee_len) > EXT_INIT_MAX_LEN);

}



static inline int ext4_ext_get_actual_len(struct ext4_extent *ext)

{

	return (int)(le16_to_cpu((ext)->ee_len) & 0x7FFF);

	return (le16_to_cpu(ext->ee_len) <= EXT_INIT_MAX_LEN ?

		le16_to_cpu(ext->ee_len) :

		(le16_to_cpu(ext->ee_len) - EXT_INIT_MAX_LEN));

}



extern int ext4_extent_tree_init(handle_t *, struct inode *);

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