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Re: [dm-devel] [PATCH 0/3] add resync speed control for dm-raid1



On Mon, Dec 10, 2012 at 01:21:23PM +1100, NeilBrown wrote:
> On Thu, 22 Nov 2012 14:27:50 +0800 Guangliang Zhao <gzhao suse com> wrote:
> 
> > Hi,
> > 
> > These patches are used to add resync speed control for dm-raid1. The
> > second and third patch provide support for user-space tool dmsetup.
> > 
> > Guangliang Zhao (3):
> >   dm raid1: add resync speed control for dm-raid1
> >   dm raid1: add interface to set resync speed
> >   dm raid1: add interface to get resync speed
> > 
> >  drivers/md/dm-raid1.c |   93 +++++++++++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 90 insertions(+), 3 deletions(-)
> > 
> 
> The problem with this approach is that it slows down resync even when there
> is no other IO happening.
> If that is deemed to be acceptable, then the patch set seems fine, though I
> would probably make the default a lot higher so as not to change current
> default behaviour for anyone.
Yes, the users who don't need this feature will not be affected, fully
accepted.

> 
> If it isn't acceptable, then you either need to monitor the number of
> requests going to the underlying devices - like md does - or monitor the
> number of requests coming in to the dm-raid1 target - which is probably
> easier with dm.
> 
> i.e. only impose the rate limit if there have been any requests for the
> dm-raid1 target in the last 'RESYNC_JIFFIES'.
Good idea, that's would be on my TODO list. But anyway these patches are
still required.

> 
> What do you think of that?
> 
> NeilBrown



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-- 
Best regards,
Guangliang


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