Re: Proposal: make RAID6 code optional
- From: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Sat, 18 Apr 2009 19:07:34 -0700
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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