RE: [PATCH 7/9] IB/core: generic RDMA READ/WRITE API

Steve Wise
2016-03-03T15:29:47Z

> >> Christoph,
> >>
> >> This is a problem for mlx5 which exposes:
> >>
> >> props->max_fast_reg_page_list_len = (unsigned int)-1;
> >>
> >> Which is obviously wrong and needs to be corrected, but this is sort of
> >> an overkill to allocate max supported unconditionally.
> >>
> >> How about choosing a sane default of 256/512 pages for now? I don't
> >> think we'll see a lot of larger transfers in iser/nvmf (which actually
> >> need MRs for iWARP).
> >>
> >> Alternatively we can allow the caller to limit the MR size?
> >
> > I'm fine with a limit in the core rdma r/w code. But why is this
> > a problem for mlx5? If it offers unlimited MR sizes it should support
> > that, or report a useful value. I don't see why fixing mlx5 should
> > be a problem, and would rather see this driver bug fixed ASAP.
>
> Already sent out a fix for mlx5. But even then, if a driver offers huge
> amount of translation entries per MR doesn't mean we need to allocate
> gigantic MRs for imaginary transfer sizes...
>
> I'd be happier if this is controlled by the caller.

Are there hard limits for iSER and NVMEF/RDMA? If so, then perhaps the caller should pass that in and the RDMA-RW will choose the
min(passed_in_max, device_max)?

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