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

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Message-ID: <CAHS8izMysKCCoAoVK9KzQrfbtFfagaPMRYSUUjKTqJ-ZwJ53oA@mail.gmail.com>
Date:   Fri, 8 Dec 2023 11:27:47 -0800
From:   Mina Almasry <almasrymina@...gle.com>
To:     David Ahern <dsahern@...nel.org>
Cc:     Shailend Chand <shailend@...gle.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kselftest@...r.kernel.org,
        bpf@...r.kernel.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Jeroen de Borst <jeroendb@...gle.com>,
        Praveen Kaligineedi <pkaligineedi@...gle.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Yunsheng Lin <linyunsheng@...wei.com>,
        Harshitha Ramamurthy <hramamurthy@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Kaiyuan Zhang <kaiyuanz@...gle.com>
Subject: Re: [net-next v1 07/16] netdev: netdevice devmem allocator

On Fri, Dec 8, 2023 at 9:56 AM David Ahern <dsahern@...nel.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