On Sun, Jul 01, 2007 at 09:48:33AM -0500, Jose R. Santos wrote:
> Is your concern due to being unable to find contiguous block in the
> case that a bad disk area is in one of the bitmap blocks? One thing we
> can do is try to search for another set of contiguous blocks and if we
> fail to find one, we can flag the block group and move to an indirect
> block approach to allocating the bitmaps. At this point, we do lose
> some of the performance benefits of BIG_BG, but we would still be able
> to use the block group.
Yes, my concern is what we might need to do if for some reason e2fsck
needs to reallocate the bitmap blocks. I don't think an indirect
block scheme is the right approach, though; we're adding a lot of
complexity for a case that probably wouldn't be used but very, very
rarely.
My proposal (as we discsused) in the call, is to implement BIG_BG as
meaning the following:
1) Implementations must understand and use the s_desc_size
superblock field to determine whether block group descriptors
are the old 32 bytes or the newer 64 bytes format.
2) Implementations must support the newer ext4_group_desc
format in particular to support bg_free_blocks_count_hi and
bg_free_inodes_count_hi
3) Implementations will relax constraints on where the
superblock, bitmaps, and inode tables for a particular block
group will be stored.
So with that, we can experiment with what size block groups really
make sense, versus using the extended metablockgroup idea, or possibly
doing both.
- Ted
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