[linux-lvm] How does LVM-Cache work?

[thornber at redhat.com]

On Wed, Feb 27, 2013 at 03:30:47PM -0300, Leo Antonio wrote:
> Thanks for answers.
> 
> 
> I take a look in dm-cache-target, I really dont knew this project.
> 
> Joe, what is the best way to continue this discussion?
> 
> Do you have some documentation besides what is into kernel source, like
> Papers, Architecture Projects etc?
> What is the best way to start to understand this?

The best place to start is by reading
Documentation/device-mapper/cache.txt and trying it out a bit.  Then
read drivers/md/dm-cache-policy.h which defines the interface that
policies use.  Finally look at dm-cache-policy-mq.c (multiqueue
policy).  This should give you a good idea of the responsibilities of
a policy.

An alternative project would be creating a framework for assessing
cache policies.  Not just providing a range of different cache loads
(though that is a big important part), but also providing feedback to
the policy developer as to how their policy could be improved.  I'd like
to see a tool that calculates the optimimum series of
promotions/demotions for a given io load and so comes up with a
theoretical 'best' performance.

- Joe