[openib-general] fmr question

[Roland Dreier]

    Steve> So this implies that there is really only one mapping
    Steve> outstanding at any point in time (less the cache issue).
    Steve> Right?  So why is there a map count as an fmr attribute?
    Steve> Its seems like just an arbitrary limit put on how many
    Steve> times you can map an fmr before unmaping.  -and- once you
    Steve> unmap you can start mapping again up to the map count... ??

Part of the L_Key and R_Key are twiddled each time the FMR is
remapped.  Because of the possibility of stale data hanging around the
cache, we don't want to reuse an old key without flushing any
translation caches.  So when we've used all the possibilities for the
changeable part of the key, we need to make sure the FMR is unmapped
(and the cache flushed) before remapping it.

The whole FMR scheme was driven by Mellanox hardware, so if there's a
way we can change things to make it more generic, I'm all for it.

 - R.