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From: Alexander Duyck <alexander.duyck@gmail.com>
To: Jesper Dangaard Brouer <jbrouer@redhat.com>
Cc: Yunsheng Lin <linyunsheng@huawei.com>,
	David Miller <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	Marcin Wojtas <mw@semihalf.com>,
	linuxarm@openeuler.org, yisen.zhuang@huawei.com,
	Salil Mehta <salil.mehta@huawei.com>,
	thomas.petazzoni@bootlin.com, hawk@kernel.org,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	John Fastabend <john.fastabend@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Will Deacon <will@kernel.org>,
	Matthew Wilcox <willy@infradead.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	fenghua.yu@intel.com, guro@fb.com, Peter Xu <peterx@redhat.com>,
	Feng Tang <feng.tang@intel.com>, Jason Gunthorpe <jgg@ziepe.ca>,
	Matteo Croce <mcroce@microsoft.com>,
	Hugh Dickins <hughd@google.com>,
	Jonathan Lemon <jonathan.lemon@gmail.com>,
	Alexander Lobakin <alobakin@pm.me>,
	Willem de Bruijn <willemb@google.com>,
	wenxu@ucloud.cn, Cong Wang <cong.wang@bytedance.com>,
	Kevin Hao <haokexin@gmail.com>,
	nogikh@google.com, Marco Elver <elver@google.com>,
	Yonghong Song <yhs@fb.com>,
	kpsingh@kernel.org, andrii@kernel.org,
	Martin KaFai Lau <kafai@fb.com>,
	songliubraving@fb.com, Netdev <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH rfc v5 2/4] page_pool: add interface to manipulate frag count in page pool
Date: Wed, 14 Jul 2021 07:46:19 -0700	[thread overview]
Message-ID: <CAKgT0UcDxSmMqCGvrWeYFiKNsxWXskF+pUhKQVCC6totduUyDQ@mail.gmail.com> (raw)
In-Reply-To: <79d9e41c-6433-efe1-773a-4f5e91e8de0f@redhat.com>

On Wed, Jul 14, 2021 at 3:18 AM Jesper Dangaard Brouer
<jbrouer@redhat.com> wrote:
>
>
>
> On 14/07/2021 11.34, Yunsheng Lin wrote:
> > As suggested by Alexander, "A DMA mapping should be page
> > aligned anyway so the lower 12 bits would be reserved 0",
> > so it might make more sense to repurpose the lower 12 bits
> > of the dma address to store the frag count for frag page
> > support in page pool for 32 bit systems with 64 bit dma,
> > which should be rare those days.
>
> Do we have any real driver users with 32-bit arch and 64-bit DMA, that
> want to use this new frag-count system you are adding to page_pool?
>
> This "lower 12-bit use" complicates the code we need to maintain
> forever. My guess is that it is never used, but we need to update and
> maintain it, and it will never be tested.
>
> Why don't you simply reject using page_pool flag PP_FLAG_PAGE_FRAG
> during setup of the page_pool for this case?
>
>   if ((pool->p.flags & PP_FLAG_PAGE_FRAG) &&
>       (sizeof(dma_addr_t) > sizeof(unsigned long)))
>     goto reject-setup;
>
>

That sounds good to me if we want to go that route. It would simplify
this quite a bit since essentially we could just drop these if blocks.

Thanks.

- Alex

  parent reply	other threads:[~2021-07-14 14:46 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-14  9:34 [PATCH rfc v5 0/4] add frag page support " Yunsheng Lin
2021-07-14  9:34 ` [PATCH rfc v5 1/4] page_pool: keep pp info as long as page pool owns the page Yunsheng Lin
2021-07-14  9:34 ` [PATCH rfc v5 2/4] page_pool: add interface to manipulate frag count in page pool Yunsheng Lin
2021-07-14 10:18   ` Jesper Dangaard Brouer
2021-07-14 10:28     ` Ilias Apalodimas
2021-07-14 14:46     ` Alexander Duyck [this message]
2021-07-15  3:49       ` Yunsheng Lin
2021-07-14  9:34 ` [PATCH rfc v5 3/4] page_pool: add frag page recycling support " Yunsheng Lin
2021-07-14  9:34 ` [PATCH rfc v5 4/4] net: hns3: support skb's frag page recycling based on " Yunsheng Lin

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