[ofa-general] max_mr limit

[Jack Morgenstein]

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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