Re: Enabling peer to peer device transactions for PCIe devices

Serguei Sagalovitch
2016-11-23T19:06:34Z

On 2016-11-23 12:27 PM, Bart Van Assche wrote:
> On 11/23/2016 09:13 AM, Logan Gunthorpe wrote:
>> IMO any memory that has been registered for a P2P transaction should be
>> locked from being evicted. So if there's a get_user_pages call it needs
>> to be pinned until the put_page. The main issue being with the RDMA
>> case: handling an eviction when a chunk of memory has been registered as
>> an MR would be very tricky. The MR may be relied upon by another host
>> and the kernel would have to inform user-space the MR was invalid then
>> user-space would have to tell the remote application.
>
> Hello Logan,
>
> Are you aware that the Linux kernel already supports ODP (On Demand
> Paging)? See also the output of git grep -nHi on.demand.paging. See
> also
> https://www.openfabrics.org/images/eventpresos/workshops2014/DevWorkshop/presos/Tuesday/pdf/04_ODP_update.pdf.
>
> Bart.
My understanding is that the main problems are (a) h/w support (b)
compatibility with IB Verbs semantic.