From: NeilBrown <neilb@suse.de>
To: Namhyung Kim <namhyung@gmail.com>
Cc: linux-raid@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [md PATCH 17/34] md/raid5: unite handle_stripe_dirtying5 and handle_stripe_dirtying6
Date: Tue, 26 Jul 2011 11:52:38 +1000 [thread overview]
Message-ID: <20110726115238.63fec583@notabene.brown> (raw)
In-Reply-To: <87tyaepto6.fsf@gmail.com>
On Fri, 22 Jul 2011 18:10:33 +0900 Namhyung Kim <namhyung@gmail.com> wrote:
> NeilBrown <neilb@suse.de> writes:
>
> > RAID6 is only allowed to choose 'reconstruct-write' while RAID5 is
> > also allow 'read-modify-write'
> > Apart from this difference, handle_stripe_dirtying[56] are nearly
> > identical. So resolve these differences and create just one function.
> >
> > Signed-off-by: NeilBrown <neilb@suse.de>
>
> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
>
> BTW, here is a question:
> Why RAID6 doesn't allow the read-modify-write? I don't think it is
> not possible, so what prevents doing that? performance? complexity?
> or it's not possible? Why? :)
The primary reason in my mind is that when Peter Anvin wrote this code he
didn't implement read-modify-write and I have never seen a need to consider
changing that.
You would need a largish array - at least 7 devices - before RWM could
possibly be a win, but some people do have arrays larger than that.
The computation to "subtract" from the Q-syndrome might be a bit complex - I
don't know.
Peter: maybe you have a reason that I haven't mentioned?
Thanks,
NeilBrown
next prev parent reply other threads:[~2011-07-26 1:52 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-21 2:32 [md PATCH 00/34] md patches for 3.1 - part 1 NeilBrown
2011-07-21 2:32 ` [md PATCH 02/34] md/raid10: factor out common bio handling code NeilBrown
2011-07-21 2:32 ` [md PATCH 01/34] md/raid10: get rid of duplicated conditional expression NeilBrown
2011-07-21 2:32 ` [md PATCH 03/34] md/raid10: share pages between read and write bio's during recovery NeilBrown
2011-07-21 2:32 ` [md PATCH 08/34] md/raid5: replace sh->lock with an 'active' flag NeilBrown
2011-07-22 4:27 ` Namhyung Kim
2011-07-22 4:49 ` NeilBrown
2011-07-22 5:03 ` Namhyung Kim
2011-08-03 22:47 ` Dan Williams
2011-08-03 23:35 ` NeilBrown
2011-08-03 23:45 ` Williams, Dan J
2011-08-04 0:18 ` NeilBrown
2011-07-21 2:32 ` [md PATCH 09/34] md/raid5: move common code into handle_stripe NeilBrown
2011-07-22 4:30 ` Namhyung Kim
2011-07-21 2:32 ` [md PATCH 06/34] md/raid5: Remove use of sh->lock in sync_request NeilBrown
2011-07-22 3:39 ` Namhyung Kim
2011-07-21 2:32 ` [md PATCH 11/34] md/raid5: add some more fields to stripe_head_state NeilBrown
2011-07-22 5:31 ` Namhyung Kim
2011-07-26 1:35 ` NeilBrown
2011-07-21 2:32 ` [md PATCH 07/34] md/raid5: Protect some more code with ->device_lock NeilBrown
2011-07-22 3:54 ` Namhyung Kim
2011-07-21 2:32 ` [md PATCH 05/34] md/raid5: get rid of duplicated call to bio_data_dir() NeilBrown
2011-07-21 2:32 ` [md PATCH 04/34] md/raid5: use kmem_cache_zalloc() NeilBrown
2011-07-21 2:32 ` [md PATCH 10/34] md/raid5: unify stripe_head_state and r6_state NeilBrown
2011-07-22 4:49 ` Namhyung Kim
2011-07-22 5:15 ` NeilBrown
2011-07-22 5:37 ` NeilBrown
2011-07-22 5:53 ` Namhyung Kim
2011-07-26 6:44 ` Namhyung Kim
2011-07-21 2:32 ` [md PATCH 16/34] md/raid5: unite fetch_block5 and fetch_block6 NeilBrown
2011-07-22 8:24 ` Namhyung Kim
2011-07-21 2:32 ` [md PATCH 17/34] md/raid5: unite handle_stripe_dirtying5 and handle_stripe_dirtying6 NeilBrown
2011-07-22 9:10 ` Namhyung Kim
2011-07-26 1:52 ` NeilBrown [this message]
2011-07-26 2:41 ` H. Peter Anvin
2011-07-26 9:40 ` David Brown
2011-07-26 13:23 ` Namhyung Kim
2011-07-26 15:01 ` David Brown
2011-07-21 2:32 ` [md PATCH 19/34] md/raid5: move some more common code into handle_stripe NeilBrown
2011-07-22 9:29 ` Namhyung Kim
2011-07-26 1:59 ` NeilBrown
2011-07-21 2:32 ` [md PATCH 12/34] md/raid5: move stripe_head_state and more " NeilBrown
2011-07-22 5:41 ` Namhyung Kim
2011-07-21 2:32 ` [md PATCH 14/34] md/raid5: move more code into common handle_stripe NeilBrown
2011-07-22 7:32 ` Namhyung Kim
2011-07-26 1:48 ` NeilBrown
2011-07-21 2:32 ` [md PATCH 15/34] md/raid5: rearrange a test in fetch_block6 NeilBrown
2011-07-22 7:37 ` Namhyung Kim
2011-07-21 2:32 ` [md PATCH 18/34] md/raid5: move more common code into handle_stripe NeilBrown
2011-07-22 9:20 ` Namhyung Kim
2011-07-21 2:32 ` [md PATCH 13/34] md/raid5: Move code for finishing a reconstruction " NeilBrown
2011-07-22 7:09 ` Namhyung Kim
2011-07-26 1:44 ` NeilBrown
2011-07-21 2:32 ` [md PATCH 24/34] md: remove ro check in md_check_recovery() NeilBrown
2011-07-21 2:32 ` [md PATCH 22/34] md/raid: use printk_ratelimited instead of printk_ratelimit NeilBrown
2011-07-21 2:32 ` [md PATCH 23/34] md: introduce link/unlink_rdev() helpers NeilBrown
2011-07-21 2:32 ` [md PATCH 20/34] md/raid5: finalise new merged handle_stripe NeilBrown
2011-07-22 9:36 ` Namhyung Kim
2011-07-26 2:02 ` NeilBrown
2011-07-26 4:50 ` Namhyung Kim
2011-07-21 2:32 ` [md PATCH 26/34] md/raid10: Make use of new recovery_disabled handling NeilBrown
2011-07-21 2:32 ` [md PATCH 27/34] md/raid10: Improve decision on whether to fail a device with a read error NeilBrown
2011-07-21 2:32 ` [md PATCH 25/34] md: change managed of recovery_disabled NeilBrown
2011-07-21 2:32 ` [md PATCH 21/34] md: use proper little-endian bitops NeilBrown
2011-07-21 2:32 ` [md PATCH 31/34] md/raid10: move rdev->corrected_errors counting NeilBrown
2011-07-21 2:32 ` [md PATCH 33/34] MD: raid1 s/sysfs_notify_dirent/sysfs_notify_dirent_safe NeilBrown
2011-07-21 2:32 ` [md PATCH 29/34] md/raid1: move rdev->corrected_errors counting NeilBrown
2011-07-21 2:32 ` [md PATCH 30/34] md/raid5: " NeilBrown
2011-07-21 2:32 ` [md PATCH 32/34] md/raid5: Avoid BUG caused by multiple failures NeilBrown
2011-07-21 2:32 ` [md PATCH 34/34] MD bitmap: Revert DM dirty log hooks NeilBrown
2011-07-21 2:32 ` [md PATCH 28/34] md: get rid of unnecessary casts on page_address() NeilBrown
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