Re: Memory providers multiplexing (Was: [PATCH net-next v4 4/5] page_pool: remove PP_FLAG_PAGE_FRAG flag)

From: Mina Almasry <almasrymina@google.com>
To: David Ahern <dsahern@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Jesper Dangaard Brouer <jbrouer@redhat.com>,
	brouer@redhat.com, Alexander Duyck <alexander.duyck@gmail.com>,
	Yunsheng Lin <linyunsheng@huawei.com>,
	davem@davemloft.net, pabeni@redhat.com, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Lorenzo Bianconi <lorenzo@kernel.org>,
	Yisen Zhuang <yisen.zhuang@huawei.com>,
	Salil Mehta <salil.mehta@huawei.com>,
	Sunil Goutham <sgoutham@marvell.com>,
	Geetha sowjanya <gakula@marvell.com>,
	Subbaraya Sundeep <sbhatta@marvell.com>,
	hariprasad <hkelam@marvell.com>,
	Saeed Mahameed <saeedm@nvidia.com>,
	Leon Romanovsky <leon@kernel.org>, Felix Fietkau <nbd@nbd.name>,
	Ryder Lee <ryder.lee@mediatek.com>,
	Shayne Chen <shayne.chen@mediatek.com>,
	Sean Wang <sean.wang@mediatek.com>, Kalle Valo <kvalo@kernel.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	AngeloGioacchino Del Regno 
	<angelogioacchino.delregno@collabora.com>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	linux-rdma@vger.kernel.org, linux-wireless@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org,
	Jonathan Lemon <jonathan.lemon@gmail.com>
Subject: Re: Memory providers multiplexing (Was: [PATCH net-next v4 4/5] page_pool: remove PP_FLAG_PAGE_FRAG flag)
Date: Wed, 5 Jul 2023 18:19:00 -0700	[thread overview]
Message-ID: <CAHS8izPF7WjMKLA82fy5LjE9XzUWNVMgs9tD7JM5UY3xfw93Yw@mail.gmail.com> (raw)
In-Reply-To: <011d3204-5c33-782c-41d1-53bf9bd2e095@kernel.org>

On Mon, Jul 3, 2023 at 10:23 AM David Ahern <dsahern@kernel.org> wrote:
>
> On 7/3/23 11:13 AM, Eric Dumazet wrote:
> > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> > index a2dbeb264f260e5b8923ece9aac99fe19ddfeb62..aa4133d1b1e0676e408499ea4534b51262394432
> > 100644
> > --- a/net/packet/af_packet.c
> > +++ b/net/packet/af_packet.c
> > @@ -2152,7 +2152,7 @@ static int packet_rcv(struct sk_buff *skb,
> > struct net_device *dev,
> >                 }
> >         }
> >
> > -       snaplen = skb->len;
> > +       snaplen = skb->devmem ? skb_headlen(skb) : skb->len;
> >
>
> Ok, so you expect a flag on the skb noting the use of 'untouchable'
> memory. That aligns with my expectations based on POCs.
>
> Based on the above: 1) skb->head is expected to be host memory, and 2)
> the flag is a global for all frags, so no mix and match.

Yes, both are correct (i.e. what I plan to propose).

-- 
Thanks,
Mina