On Tue, Nov 3, 2026 at 3:51 PM Stanislav Fomichev [off-list ref] wrote:
TX bindings use PAGE_SIZE net_iovs, so a frag covers at most a page.
A 64KB skb needs 16 frags, and MAX_SKB_FRAGS caps devmem skbs at about
68KB, which makes BIG TCP ineffective for devmem TX.
This series picks the TX net_iov size from the dmabuf sg table instead:
the largest power of 2, up to 2MB, which aligns every DMA segment. With
a 2MB hugepage-backed udmabuf a BIG TCP skb takes a few frags. There's
no UAPI change since TX addresses are dmabuf offsets.
TCP still bounds skbs by size_goal, so frags get larger, skbs don't.
A single frag can now be as large as the skb, which matters for
NETMEM_TX drivers with tso_max_size above 64KB:
- mlx5: 32-bit length per data segment
- gve: splits frags into 16KB descriptors
- fbnic: keeps the default 64KB tso_max_size
- bnxt: 16-bit BD length, devmem TX frags are capped at 32KB by a new
per-device limit
Reviewed-by: Mina Almasry <redacted>