[PATCH v5 1/5] RDMA/umem: Support importing dma-buf as user memory region

[Xiong, Jianxin]

> -----Original Message-----
> From: Jason Gunthorpe <jgg at ziepe.ca>
> Sent: Friday, October 16, 2020 12:00 PM
> To: Xiong, Jianxin <jianxin.xiong at intel.com>
> Cc: linux-rdma at vger.kernel.org; dri-devel at lists.freedesktop.org; Doug Ledford <dledford at redhat.com>; Leon Romanovsky
> <leon at kernel.org>; Sumit Semwal <sumit.semwal at linaro.org>; Christian Koenig <christian.koenig at amd.com>; Vetter, Daniel
> <daniel.vetter at intel.com>
> Subject: Re: [PATCH v5 1/5] RDMA/umem: Support importing dma-buf as user memory region
> 
> On Thu, Oct 15, 2020 at 03:02:45PM -0700, Jianxin Xiong wrote:
> 
> > +static void ib_umem_dmabuf_invalidate_cb(struct dma_buf_attachment
> > +*attach) {
> > +	struct ib_umem_dmabuf *umem_dmabuf = attach->importer_priv;
> > +
> > +	dma_resv_assert_held(umem_dmabuf->attach->dmabuf->resv);
> > +
> > +	ib_umem_dmabuf_unmap_pages(&umem_dmabuf->umem, true);
> > +	queue_work(ib_wq, &umem_dmabuf->work);
> 
> Do we really want to queue remapping or should it wait until there is a page fault?

Queuing remapping here has performance advantage because it reduces the chance
of getting the page fault.

> 
> What do GPUs do?
> 
> Jason