Re: [PATCH net-next 4/7] net: devmem: add a per-device netmem TX frag size limit

[Stanislav Fomichev]

On 11/02, Mina Almasry wrote:
> On Mon, Nov 2, 2026 at 11:14 AM Stanislav Fomichev <sdf.kernel@xxxxxxxxx> wrote:
> >
> > Devmem TX frags are bounded only by the net_iov size, which is about
> > to grow up to 2MB, more than some devices can describe in a single TX
> > descriptor.
> >
> > Add netmem_tx_max_frag_size, U32_MAX by default, and cap devmem TX
> > frags to the limit of the device the binding is attached to.
> >
> > Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxxx>
> 
> Abstractly LGTM but I'm not sure why this is TX-specific. Didn't we
> add non-PAGE_SIZE rx net-iovs? This should have been a problem then.
> Either you know what you're doing (maybe document in the commit
> message) or we need some more alignment on RX and TX.
> 
> TBH I was dissapointed when LLMs started reporting that
> binding->vdev/dev are treated very differently for RX and TX and I
> have to write a cleanup that consolidates this:
> 
> https://github.com/mina/linux/compare/devmem-teardown-v4...devmem-lease-bind-map-dev
> 
> I think maybe my reviews and yours maybe should be more mindful about
> keeping these memory things consolidated and as much as possible not
> RX/TX specific.

This patch is mostly a bandaid for bnxt which can't express sizes
longer than 2^16-1 in its tx descriptors. And rx is even more restricted
I think? Up to 32K HW GRO aggregated?