linux-kernel - Re: [ 024/167] [PATCH] md: dont call ->add

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Message-ID: <20120509172022.73159017@notabene.brown>
Date:	Wed, 9 May 2012 17:20:22 +1000
From:	NeilBrown <neilb@...e.de>
To:	Jonathan Nieder <jrnieder@...il.com>
Cc:	Ben Hutchings <ben@...adent.org.uk>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Jan Ceuleers <jan.ceuleers@...puter.org>
Subject: Re: [ 024/167] [PATCH] md: dont call ->add_disk unless there is
 good reason.

On Wed, 9 May 2012 01:57:17 -0500 Jonathan Nieder <jrnieder@...il.com> wrote:

> Hi,
> 
> Ben Hutchings wrote:
> 
> > 3.2-stable review patch.  If anyone has any objections, please let me know.
> [...]
> > commit ed209584c38fb74b7eecc03e5b1bfe674e591bd8 upstream.
> >
> > Commit 7bfec5f35c68121e7b18
> >
> >    md/raid5: If there is a spare and a want_replacement device, start replacement.
> >
> > cause md_check_recovery to call ->add_disk much more often.
> > Instead of only when the array is degraded, it is now called whenever
> > md_check_recovery finds anything useful to do, which includes
> > updating the metadata for clean<->dirty transition.
> > This causes unnecessary work, and causes info messages from ->add_disk
> > to be reported much too often.
> 
> Does 3.2.y need this?  Commit 7bfec5f35c68121e7b18 (aka v3.3-rc3~3^2~22)
> does not seem to be part of the 3.2-stable tree.
> 
> Jonathan

Thanks for checking!

Probably not needed then, but it wouldn't be harmful.

NeilBrown


> 
> > So refine md_check_recovery to only do any actual recovery checking
> > (including ->add_disk) if MD_RECOVERY_NEEDED is set.
> > 
> > This fix is suitable for 3.3.y:
> > 
> > Reported-by: Jan Ceuleers <jan.ceuleers@...puter.org>
> > Signed-off-by: NeilBrown <neilb@...e.de>
> > Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
> > ---
> >  drivers/md/md.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index b572e1e..8beb19c 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -7560,14 +7560,14 @@ void md_check_recovery(struct mddev *mddev)
> >  		 * any transients in the value of "sync_action".
> >  		 */
> >  		set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
> > -		clear_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
> >  		/* Clear some bits that don't mean anything, but
> >  		 * might be left set
> >  		 */
> >  		clear_bit(MD_RECOVERY_INTR, &mddev->recovery);
> >  		clear_bit(MD_RECOVERY_DONE, &mddev->recovery);
> >  
> > -		if (test_bit(MD_RECOVERY_FROZEN, &mddev->recovery))
> > +		if (!test_and_clear_bit(MD_RECOVERY_NEEDED, &mddev->recovery) ||
> > +		    test_bit(MD_RECOVERY_FROZEN, &mddev->recovery))
> >  			goto unlock;
> >  		/* no recovery is running.
> >  		 * remove any failed drives, then


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