[RFC PATCH v2 0/3] RDMA: add dma-buf support

[Christian König]

Am 03.07.20 um 15:14 schrieb Jason Gunthorpe:
> On Fri, Jul 03, 2020 at 02:52:03PM +0200, Daniel Vetter wrote:
>
>> So maybe I'm just totally confused about the rdma model. I thought:
>> - you bind a pile of memory for various transactions, that might
>> happen whenever. Kernel driver doesn't have much if any insight into
>> when memory isn't needed anymore. I think in the rdma world that's
>> called registering memory, but not sure.
> Sure, but once registered the memory is able to be used at any moment with
> no visibilty from the kernel.
>
> Unlike GPU the transactions that trigger memory access do not go
> through the kernel - so there is no ability to interrupt a command
> flow and fiddle with mappings.

This is the same for GPUs with user space queues as well.

But we can still say for a process if that this process is using a 
DMA-buf which is moved out and so can't run any more unless the DMA-buf 
is accessible again.

In other words you somehow need to make sure that the hardware is not 
accessing a piece of memory any more when you want to move it.

Christian.

>
> Jason