[ofa-general] max_mr limit

[Rajouri Jammu]

Thanks for all the responses.

If I have to register large amounts of memory from user space, it's still
unclear to me what's the best (predictable) way to do it today?

Since there is a limit, how do I figure out the exact limit?

As I was able to register almost 20GB in 10MB chunks I'm not sure why I
didn't hit the 2^20*4K limit on the MTTs.

Any clarifications would be most helpful.

thanks!


On Mon, Mar 17, 2008 at 3:12 AM, Jack Morgenstein <jackm at dev.mellanox.co.il>
wrote:

> On Monday 17 March 2008 09:22, Or Gerlitz wrote:
> > Rajouri Jammu wrote:
> > > Does that mean that no matter how I size my memory regions the maximum
> > > amount of (total) memory I can register is = 2^20 * 4K = 4GB?
> > > I.e., Am I limited by the total number of MTTs?
> > Generally speaking, yes, the IB network MMU (MTT this case) is limited
> > in the number of slots it has and so in the amount of memory it can map
> > at once, but I assume this is typical eg for I/O MMUs and makes sense.
> >
> > However, each slot can map --more-- then 4K, so one should be able to
> > use huge-pages etc. I am not sure what is the actual status of
> > registering huge-pages by the Linux IB stack, maybe Roland can comment
> > on that.
> >
> > Or.
>
> In Mellanox HCAs, each memory region (i.e., mpt) can specify how many
> pages
> each mtt entry it uses represents. This would allow a much larger number
> of
> large regions to be mapped (essentially eliminating the current
> limitation).
>
> Currently, this feature is not supported by the driver code.
>
> - Jack
> >
> >
> >
>
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