Matti Aarnio wrote:
On Sat, Apr 18, 2009 at 03:56:17PM +0200, Jesper Juhl wrote:
On Sat, 18 Apr 2009, Prakash Punnoor wrote:
On Samstag 18 April 2009 10:09:54 Michael Tokarev wrote:
Prakash Punnoor wrote:
.....
What's your goal? What's the problem you're trying to solve?
Having duplicate code is not good, of course. But unused code is also not
good. As I said, I only use RAID5, so I don't need RAID6 support. The RAID6
support enlarges kernel (the built-in.o in drivers/md grows from 325kb to
414kb in my case), making boot time and compile time longer
By a few ms perhaps - nothing that you'd ever notice in real life... A
small price to pay for the shared code. If you were to split them all
again, the combined total size would be greater still.
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
It would seem that that space could be allocated and populated when
raid6 was first used, as part of the initialization. I haven't looked at
that code since it was new, so I might be optimistic about doing it that
way.
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.
There are perhaps a few kB more of codes for RAID5 and RAID6 classes - not all
local functions at each are named with relevant prefix, but overall I would
consider extracting RAID6 as a reasonable goal with common codes on RAID4/5.
- admittedly not
by a big margin. But then again I could argue: Why not put RAID0,1,10,4,5,6
into one big module? Makes no sense, huh?
Makes perfect sense to me. Just modprobe raid.o and you have all
raid levels available. That would make a lot of sense.
Also, systems with so many disks that they run RAID4/5/6 to begin with are
likely to have enough memory so that "wasted" 75-80 kB does not matter.
Everything matters. "Take care of the pennies and the dollars will take
care of themselves" is not just an old German proverb.
--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
"You are disgraced professional losers. And by the way, give us our money back."
- Representative Earl Pomeroy, Democrat of North Dakota
on the A.I.G. executives who were paid bonuses after a federal bailout.
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