[PATCH 6/8] nvme-pci: convert the data mapping to blk_rq_dma_map
Keith Busch
kbusch at kernel.org
Mon Jun 23 08:44:05 PDT 2025
On Mon, Jun 23, 2025 at 04:12:28PM +0200, Christoph Hellwig wrote:
> Use the blk_rq_dma_map API to DMA map requests instead of scatterlists.
> This removes the need to allocate a scatterlist covering every segment,
> and thus the overall transfer length limit based on the scatterlist
> allocation.
>
> Instead the DMA mapping is done by iterating the bio_vec chain in the
> request directly. The unmap is handled differently depending on how
> we mapped:
>
> - when using an IOMMU only a single IOVA is used, and it is stored in
> iova_state
> - for direct mappings that don't use swiotlb and are cache coherent,
> unmap is not needed at all
> - for direct mappings that are not cache coherent or use swiotlb, the
> physical addresses are rebuild from the PRPs or SGL segments
>
> The latter unfortunately adds a fair amount of code to the driver, but
> it is code not used in the fast path.
>
> The conversion only covers the data mapping path, and still uses a
> scatterlist for the multi-segment metadata case. I plan to convert that
> as soon as we have good test coverage for the multi-segment metadata
> path.
Looks good.
Reviewed-by: Keith Busch <kbusch at kernel.org>
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