[RFC v2 00/11] Add dmabuf read/write via io_uring

[Anuj gupta]

This series significantly reduces the IOMMU/DMA overhead for I/O,
particularly when the IOMMU is configured in STRICT or LAZY mode. I
modified t/io_uring in fio to exercise this path and tested with an
Intel Optane device. On my setup, I see the following improvement:

- STRICT: before = 570 KIOPS, after = 5.01 MIOPS
- LAZY: before = 1.93 MIOPS, after = 5.01 MIOPS
- PASSTHROUGH: before = 5.01 MIOPS, after = 5.01 MIOPS

The STRICT/LAZY numbers clearly show the benefit of avoiding per-I/O
dma_map/dma_unmap and reusing the pre-mapped DMA addresses.
--
Anuj Gupta