Re: [PATCH v4 08/14] nvme-pci: implement dma_token backed requests

[Caleb Sander Mateos]

On Thu, Jul 30, 2026 at 4:36 AM Anuj Gupta/Anuj Gupta
<anuj20.g@xxxxxxxxxxx> wrote:
>
> On 7/30/2026 4:11 PM, Pavel Begunkov wrote:
> >>
> >> I wonder if it's possible to perform the PRP list page allocations and
> >> initialization in nvme_dma_buf_io_map() instead of the I/O path. The
> >> NVMe dma_pools are per-NUMA-node linked lists protected by spinlocks,
> >> making them significant CPU hotspots. If the dmabuf registration set
> >> up a contiguous DMA-coherent list of PRP entries for the pages of the
> >> registered buffer, any command using the dmabuf and requiring at most
> >> 1 PRP list page (i.e. length <= 2 MB) could just set its PRP list
> >> pointer to an offset into the dmabuf's PRP list.
> >
> > Possible to an extent, predecessor patches tried that, I left it for
> > later to keep the series simpler. I guess chaining won't work in
> > general case.
> > I mentioned this to Kanchan, Anuj and Nitesh before, they were up to
> > playing with nvme optimisations in general, and since sgl from Anuj
> > is ready, maybe they already have a prototype somewhere for that.
> >
>
> Right, I have prototyped the PRP list optimisation before. I will send
> it once the initial version of this series lands, to avoid adding new
> review churn while the rest of the series is pretty settled.

Sure, landing it subsequently makes sense. Glad to hear it's already
in the works.

Thanks,
Caleb