Re: [PATCH] 2.4.0-test7 to Enable Variable Block Chaining

From: Neil Brown (
Date: Mon Sep 04 2000 - 19:59:30 EST

On Saturday September 2, wrote:
> Linus,
> The attached patch is submitted to enable variable sector size block
> chaining via ll_rw_block() in the I/O subsystem layer.
> Jeff904a905,907
> > /****
> > // This code is being commented out to allow support for variable chained
> > // block I/O requests. Jeff V. Merkey
> 915a919
> > *****/

While I think this patch is a good idea, I feel I should let you know
that using the functionality on a Software-RAID-5 device will cause
terrible performance.
Whenever raid5.c notices the block size has changed, it flushes it's
stripe cache, and rebuilds it with the new size. This effectively
serialises requests around any size change.

Fixing this in on my todo list, but I haven't come up with a really
neat model yet.

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