[openib-general] Re: user_mad: large rmpp length problem

[Sean Hefty]

Michael S. Tsirkin wrote:
> This approach still means that we have to allocate a potentially
> huge amount of memory to copy all of the rmpp mad into kernel
> in one go.
> 
> What I had in mind was: add a get_next_segment callback to mad,
> which would copy the data (by copy_from_user) incrementally,
> making forward progress without requiring us to have all of the mad
> in kernel memory.

This may work.  I think that there may be issues with respect to providing 
proper synchronization and handling retries, but without looking at an 
implementation, I can't be sure.

Is support for large RMPP transfers needed for kernel clients?  If not, then we 
may be able to implement this entirely in userspace, provided an option were 
given to disable it in the kernel.

- Sean