linux-kernel - Re: Proposal: make RAID6 code optional

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Message-ID: <49EA8766.9070605@zytor.com>
Date:	Sat, 18 Apr 2009 19:07:34 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Matti Aarnio <matti.aarnio@...iler.org>
CC:	Jesper Juhl <jj@...osbits.net>,
	Prakash Punnoor <prakash@...noor.de>,
	Michael Tokarev <mjt@....msk.ru>, linux-kernel@...r.kernel.org,
	linux-raid@...r.kernel.org, neilb@...e.de
Subject: Re: Proposal: make RAID6 code optional

Matti Aarnio wrote:
> 
> I did quick "sum of symbol sizes" lookup of the   raid.ko, and got
> it like this:
> 
> nm -t d -n -S /lib/modules/2.6.27.21-170.2.56.fc10.x86_64/kernel/drivers/md/raid456.ko | grep raid4|awk '{print $2}'|sed -e 's/^0*//g'|awk '{sum+=$1}END{print sum}'
>   ...
> 
> raid4:   152
> raid5:  7165
> raid6: 75558
> 
> Entire 64kB of that raid6 is single pre-initialized r/o datablock:  raid6_gfmul
> 
> So yes, having RAID6 personality as separate module would be appropriate for
> systems that are only interested in RAID4 or RAID5.  Separating the RAID4
> personality wastes space, separating RAID5 ...  barely 2 of 4k memory pages.
> 

RAID 4 is really just another layout scheme for RAID 5.  But yes, moving
RAID 6 to a separate module makes sense.  The amount of RAID 5 code not
used by RAID 6 is fairly trivial, so the right way to do this is to have
 the raid6 module depend on the raid5 module.

There used to be a raid6 module which was forked from raid5, with a lot
of duplicate code.  That really made really no sense.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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