Re: [net-next v1 07/16] netdev: netdevice devmem allocator

From: Mina Almasry <almasrymina@google.com>
To: David Ahern <dsahern@kernel.org>
Cc: "Shailend Chand" <shailend@google.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-kselftest@vger.kernel.org, bpf@vger.kernel.org,
	linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
	"David S. Miller" <davem@davemloft.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Paolo Abeni" <pabeni@redhat.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Jeroen de Borst" <jeroendb@google.com>,
	"Praveen Kaligineedi" <pkaligineedi@google.com>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>,
	"Ilias Apalodimas" <ilias.apalodimas@linaro.org>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Willem de Bruijn" <willemdebruijn.kernel@gmail.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Sumit Semwal" <sumit.semwal@linaro.org>,
	"Christian König" <christian.koenig@amd.com>,
	"Yunsheng Lin" <linyunsheng@huawei.com>,
	"Harshitha Ramamurthy" <hramamurthy@google.com>,
	"Shakeel Butt" <shakeelb@google.com>,
	"Willem de Bruijn" <willemb@google.com>,
	"Kaiyuan Zhang" <kaiyuanz@google.com>
Subject: Re: [net-next v1 07/16] netdev: netdevice devmem allocator
Date: Fri, 8 Dec 2023 11:27:47 -0800	[thread overview]
Message-ID: <CAHS8izMysKCCoAoVK9KzQrfbtFfagaPMRYSUUjKTqJ-ZwJ53oA@mail.gmail.com> (raw)
In-Reply-To: <462da4bf-34f8-40c4-8772-9850b3127baf@kernel.org>

On Fri, Dec 8, 2023 at 9:56 AM David Ahern <dsahern@kernel.org> wrote:
>
> On 12/7/23 5:52 PM, Mina Almasry wrote:
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index b8c8be5a912e..30667e4c3b95 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -2120,6 +2120,41 @@ static int netdev_restart_rx_queue(struct net_device *dev, int rxq_idx)
> >       return err;
> >  }
> >
> > +struct page_pool_iov *netdev_alloc_dmabuf(struct netdev_dmabuf_binding *binding)
> > +{
> > +     struct dmabuf_genpool_chunk_owner *owner;
> > +     struct page_pool_iov *ppiov;
> > +     unsigned long dma_addr;
> > +     ssize_t offset;
> > +     ssize_t index;
> > +
> > +     dma_addr = gen_pool_alloc_owner(binding->chunk_pool, PAGE_SIZE,
>
> Any reason not to allow allocation sizes other than PAGE_SIZE? e.g.,
> 2048 for smaller MTUs or 8192 for larger ones. It can be a property of
> page_pool and constant across allocations vs allowing different size for
> each allocation.

Only for simplicity. Supporting non-PAGE_SIZE is certainly possible,
but in my estimation it's a huge can of worms worthy of itss own
series. I find this series complicated to implement and review and
support as-is, and if reasonable I would like to punt that as a future
improvement.

At the minimum, I think the needed changes are:

1. The memory provider needs to report to the page pool the alloc size.
2. The page_pool needs to handle non-PAGE_SIZE memory regions.
3. The drivers need to handle non-PAGE_SIZE memory regions. Drivers
today handle fragged pages, but that is different because it's a
PAGE_SIZE region that is fragged. This is a non-PAGE_SIZE region in
the first place.
4. Any PAGE_SIZE assumptions in the entire net stack need to be removed.

At Google we mostly use page aligned MTUs so we're likely not that
interested in sub PAGE_SIZE allocations, but we are interested in n *
PAGE_SIZE allocations, but, I hope, in a separate followup effort.

-- 
Thanks,
Mina