Re: [PATCH v2 5/5] swiotlb: Implement RX nocopy with fast recycling eviction

[Dragos Tatulea <dtatulea@nvidia.com>]

On 24.08.26 17:29, Luigi Rizzo wrote:
> Conditionally divert receive buffer allocations in page_pool
> to the SWIOTLB page allocator.
> 
> This only happens when swiotlb usage is below the threshold set by module
> parameter swiotlb.nocopy_rx_percent (default 0, range 0..90).
> A value of 0 disables the feature.
> 
> To prevent existing DRAM or SWIOTLB pages from circulating indefinitely
> in the lockless receive ring after changing the parameter at runtime,
> __page_pool_put_page() checks residency against the active parameter
> state. Mismatched pages are immediately evicted back to their
> respective allocators, achieving rapid, lockless mode conversion across
> active network streams without requiring interface or queue resets.
> 
This could be a separate page_pool allocator. It could be similar to
how ZC works: pre-allocate some coherent DMA buffers and allocate
from there.

Thanks,
Dragps