[RFC][PATCH] ChunkFS: fs fission for faster fsck

[Amit Gud <gud@cis.ksu.edu>]

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This is an initial implementation of ChunkFS technique, briefly discussed
at: http://lwn.net/Articles/190222 and 
http://cis.ksu.edu/~gud/docs/chunkfs-hotdep-val-arjan-gud-zach.pdf

This implementation is done within ext2 driver. Every chunk is an 
independent ext2 file system. The knowledge about chunks is kept within 
ext2 and 'continuation inodes', which are used to allow files and 
directories span across multiple chunks, are managed within ext2.

At mount time, super blocks for all the chunks are created and linked with 
the global super_blocks list maintained by VFS. This allows independent 
behavior or individual chunks and also helps writebacks to happen 
seamlessly.

Apart from this, chunkfs code in ext2 effectively only provides knowledge of:

- what inode's which block number to look for, for a given file's logical 
block number
- in which chunk to allocate next inode / block
- number of inodes to scan when a directory is being read

To maintain the ext2's inode number uniqueness property, 8 msb bits of 
inode number are used to indicate the chunk number in which it resides.

As said, this is a preliminary implementation and lots of changes are 
expected before this code is even sanely usable. Some known issues and 
obvious optimizations are listed in the TODO file in the chunkfs patch.

http://cis.ksu.edu/~gud/patches/chunkfs-v0.0.8.patch
- one big patch
- applies to 2.6.18

Attached - ext2-chunkfs-diff.patch.gz
- since the code is a spin-off of ext2, this patch explains better what
   has changed from the ext2.

git://cislinux.cis.ksu.edu/chunkfs-tools
- mkfs, and fsck for chunkfs.

http://cis.ksu.edu/~gud/patches/config-chunkfs-2.6.18-uml
- config file used; tested mostly on UML with loopback file systems.

NOTE: No xattrs and xips yet, CONFIG_EXT2_FS_XATTR and CONFIG_EXT2_FS_XIP 
should be "no" for clean compile.


Please comment, suggest, criticize. Patches most welcome.


Best,
AG
--
May the source be with you.
http://www.cis.ksu.edu/~gud

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