[dm-devel] Re: md: Use new topology calls to indicate alignment and I/O sizes

[Mike Snitzer]

On Wed, Jun 24 2009 at 11:27am -0400,
Mike Snitzer <snitzer at redhat.com> wrote:

> For some reason I thought you were aware of what Martin had put
> together.  I assumed as much given you helped sort out some MD interface
> compile fixes in linux-next relative to topology-motivated changes.
> Anyway, not your fault that you didn't notice the core topology
> support.. It is likely a function of Martin having implemented the MD
> bits; you got this topology support "for free"; whereas I was forced to
> implement DM's topology support (and a few important changes to the core
> infrastructure).

Got these inverted:

> Here is a thread from April that discusses the core of the topology
> support:

http://marc.info/?t=124055146700007&r=1&w=4
 
> This post touches on naming and how userland tools are expected to
> consume the topology metrics:

http://marc.info/?l=linux-ide&m=124058535512850&w=4

> 
> This post talks about the use of sysfs:
> http://marc.info/?l=linux-ide&m=124058543713031&w=4

...

> While I agree that adding these generic topology metrics to 'queue' may
> not be the perfect place I don't feel 'bdi' really helps userland
> understand them any better.  Nor would userland really care.  But I do
> agree that 'bdi' is likely a better place.
> 
> You had mentioned your goal of removing MD's 'queue' entirely. Well DM
> already had that but Martin exposed a minimalist one as part of
> preparations for the topology support, see commit:
> cd43e26f071524647e660706b784ebcbefbd2e44
> 
> This 'bdi' vs 'queue' discussion really stands to cause problems for
> userland.  It would be unfortunate to force tools be aware of 2 places.
> Rather than "phase out legacy usage" of these brand new topology limits
> it would likely be wise to get it right the first time.  Again, I'm OK
> with 'queue'; but Neil if you feel strongly about 'bdi' we should get a
> patch to Linus ASAP for 2.6.31.
> 
> I can take a stab at it now if you don't have time.

On 2nd thought, bdi is inherently tied to mm and doesn't feel 'right';
I'll defer to Martin and Jens on this.

Regards,
Mike