[RFC][PATCH 0/12]ext4: online defrag (ver 0.95)

[Akira Fujita <a-fujita@rs.jp.nec.com>]

Hi,

I've updated the ext4 online defragmentation patches.
In this version, mainly there are following two changes and some fixes:
  - Support 1KB and 2KB block size.
  - Implement EXT4_IOC_FIEMAP_INO instead of EXT4_IOC_EXTENTS_INFO
    to get extetns information.

Changelog:
- 0.95(Sep. 26, 2008)
  - Support 1KB and 2KB block size.
  - Implement EXT4_IOC_FIEMAP_INO which calls ext4_fiemap() for specified inode number
    instead of EXT4_IOC_EXTENTS_INFO to get extents information.
  - Merge "JC6-defrag-alloc-contiguous-blks-credit" and
    "ext4-request-for-blocks-with-ar.excepted_group-1.patch" in the ext4 patch queue
    into this version.
  - Handle s_dirtyblocks_counter correctly in defrag when delalloc enabled.
  - Remove unneeded copy_from_user() in EXT4_IOC_GROUP_INFO ioctl.  Ted pointed this out.
- 0.9 (May 30, 2008)
  - Create some new functions (ext4_defrag_fill_ar(),
    ext4_defrag_check_phase() ...) to separate block allocation function,
    since the phase mode plug into the allocation function isn't good.
  - Add the description of ext4_defrag() which is main function.
  - Add the capability check.
  - Some cleanups.
- 0.8 (Apr. 8, 2008)
    Fix sparse warnings and change the construction of patches.

Outline for ext4 online defragmentation:
Ext4 online defrag has the following three functions.

 no option  Solving a single file fragmentation.
            Single file fragmentation is solved by moving file
            data to contiguous free blocks.

    -r      Solving a relevant file fragmentation.
            Relevant file fragmentation could be solved by moving
            the files under the specified directory close together with
            the block containing the directory data.

    -f      Solving a free space fragmentation.
            If there is no contiguous free blocks in the filesystem,
            the other files are moved to make sufficient space to allocate
            contiguous blocks for the target file.

Notes:
- Ext4 online defarg needs "mballoc" and "extents" mount options.
- "ext4-fiemap.patch" in the ext4 patch queue is necessary
   for EXT4_IOC_FIEMAP_INO ioctl.  We have to apply fiemap patches previously
   then apply defrag patches, so it is necessary to change
   the order of series in the ext4 patch queue.

Next steps:
1. Address the following items that Ted pointed out.
 - Move all of the defrag ioctls from ext4_defrag_ioctl() to ext4_ioctl()
   so that defrag does not have a double layer ioctl's dispatch.
 - Remove the block reservation in the force defrag (-f).
 - Remove the EXT4_IOC_FIBMAP ioctl and use the EXT4_IOC_FIEMAP instead.
 - Get super block information with opening block device in user space
   so that we can remove the EXT4_IOC_GROUP_INFO ioctl.

Summary of patches:
* The followings are new ext4 online defrag patches and they consist
  of ioctl unit except 1-4.  Because the EXT4_IOC_DEFRAG is too big to review,
  I divided it into 4 patches.

[PATCH 1/12] EXT4_IOC_DEFRAG ioctl and main functions of defrag
- Create the temporary inode and do defrag per
  defrag_size (defalut 64MB).

[PATCH 2/12] Allocate new contiguous blocks with mballoc
- Search contiguous free blocks with mutil-block allocation
  and allocate them for the temporary inode.

[PATCH 3/12] Read and write file data with memory page
- Read the file data from the old blocks to the page cache and
  write the file data on the page into the new blocks.

[PATCH 4/12]  Exchange the blocks between two inodes
- Exchange the data blocks between the temporary inode and
  the original inode.

[PATCH 5/12] EXT4_IOC_FIBMAP ioctl
- The EXT4_IOC_FIBMAP ioctl gets the physical block offset of target inode
  with ext4_bmap().  This ioctl is used only in the relevant defrag (-r).

[PATCH 6/12] EXT4_IOC_GROUP_INFO ioctl
- The EXT4_IOC_GROUP_INFO ioctl gets the block group information
  of target inode is located in.  This ioctl is used only in the force defrag (-f).

[PATCH 7/12] EXT4_IOC_FREE_BLOCKS_INFO ioctl
- The EXT4_IOC_FREE_BLOCKS_INFO ioctl gets free extents
  information of the target block group.
  This ioctl is used only in the force defrag (-f).

[PATCH 8/12] EXT4_IOC_FIEMAP_INO ioctl
- The EXT4_IOC_FIEMAP_INO is used to get extents information of
  inode which set to ioctl.
  The defragger uses this ioctl to check the fragment condition
  and to get extents information in the specified block group.

[PATCH 9/12] EXT4_IOC_RESERVE_BLOCK ioctl
- The EXT4_IOC_RESERVE_BLOCK ioctl reserves the specified
  contiguous free space with ext4 block reservation function.
  This ioctl is used only in the force defrag (-f).

[PATCH 10/12] EXT4_IOC_MOVE_VICTIM ioctl
- The EXT4_IOC_MOVE_VICTIM moves the victim extents into other block group.
  Therefore the contiguous free space is made in the target block group.
  This ioctl is used only in the force defrag (-f).

[PATCH 11/12] EXT4_IOC_BLOCK_RELEASE ioctl
- The EXT4_IOC_BLOCK_RELEASE releases the reserved blocks
  which target inode holds.
  This ioctl is used if defrag failed and it was after the block reservation.

[PATCH 12/12] Online defrag command
- The defrag command. Usage is as follows:
  - Defrag for a single file.
    # e4defrag file-name
  - Defrag for all files on ext4.
    # e4defrag device-name
  - Put the multiple files closer together.
    # e4defrag -r directory-name
  - Defrag for free space fragmentation.
    # e4defrag -f file-name

Any comments and tests are welcome.

Best regards,
Akira Fujita