Re: Block fragments in ext2

From: Alexander Viro (viro@math.psu.edu)
Date: Tue Apr 18 2000 - 08:12:47 EST


On Tue, 18 Apr 2000, Stephen C. Tweedie wrote:

> Most of the advantage, though, lies in the lower amount of metadata
> required for the mapping tree if you have a larger blocksize. I'd much
> prefer to see us end up with btree-based mapping trees and a small
> blocksize rather than large blocks with standard indirection mapping
> tables as a final solution, as that really ought to gain the best of
> both worlds: small-blocksize allocation efficiency with large-blocksize
> metadata performance.

Ouch. b-tree => potentially unbound amount of blocks to be written
during the operation. Allocation efficiency is doable with fragments -
e.g. 32k/4k blocks/fragments should not be worse that 4k/4k in that
respect. Besides, we _already_ have the relevant code - turning the
preallocation logics into fragments one would not be too large change.

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