Re: [LSF/MM/BPF TOPIC] dmabuf backed read/write

Jason Gunthorpe
2026-02-05T17:41:55Z

On Tue, Feb 03, 2026 at 02:29:55PM +0000, Pavel Begunkov wrote:

> The proposal consists of two parts. The first is a small in-kernel
> framework that allows a dma-buf to be registered against a given file
> and returns an object representing a DMA mapping.

What is this about and why would you need something like this?

The rest makes more sense - pass a DMABUF (or even memfd) to iouring
and pre-setup the DMA mapping to get dma_addr_t, then directly use
dma_addr_t through the entire block stack right into the eventual
driver.

> Tushar was helping and mention he got good numbers for P2P transfers
> compared to bouncing it via RAM.

We can already avoid the bouncing, it seems the main improvements here
are avoiding the DMA map per-io and allowing the use of P2P without
also creating struct page. Meanginful wins for sure.

Jason