From: Yunsheng Lin <linyunsheng@huawei.com>
To: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Matteo Croce <mcroce@linux.microsoft.com>,
<netdev@vger.kernel.org>, <linux-mm@kvack.org>,
Ayush Sawal <ayush.sawal@chelsio.com>,
"Vinay Kumar Yadav" <vinay.yadav@chelsio.com>,
Rohit Maheshwari <rohitm@chelsio.com>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
Marcin Wojtas <mw@semihalf.com>,
Russell King <linux@armlinux.org.uk>,
Mirko Lindner <mlindner@marvell.com>,
Stephen Hemminger <stephen@networkplumber.org>,
"Tariq Toukan" <tariqt@nvidia.com>,
Jesper Dangaard Brouer <hawk@kernel.org>,
"Alexei Starovoitov" <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
"John Fastabend" <john.fastabend@gmail.com>,
Boris Pismenny <borisp@nvidia.com>, Arnd Bergmann <arnd@arndb.de>,
Andrew Morton <akpm@linux-foundation.org>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Vlastimil Babka <vbabka@suse.cz>, Yu Zhao <yuzhao@google.com>,
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Michel Lespinasse <walken@google.com>,
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Hugh Dickins <hughd@google.com>, Peter Xu <peterx@redhat.com>,
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Guoqing Jiang <guoqing.jiang@cloud.ionos.com>,
Jonathan Lemon <jonathan.lemon@gmail.com>,
Alexander Lobakin <alobakin@pm.me>,
Cong Wang <cong.wang@bytedance.com>, wenxu <wenxu@ucloud.cn>,
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Aleksandr Nogikh <nogikh@google.com>,
Jakub Sitnicki <jakub@cloudflare.com>,
Marco Elver <elver@google.com>,
Willem de Bruijn <willemb@google.com>,
Miaohe Lin <linmiaohe@huawei.com>,
Guillaume Nault <gnault@redhat.com>,
<linux-kernel@vger.kernel.org>, <linux-rdma@vger.kernel.org>,
<bpf@vger.kernel.org>, Matthew Wilcox <willy@infradead.org>,
Eric Dumazet <edumazet@google.com>,
David Ahern <dsahern@gmail.com>,
Lorenzo Bianconi <lorenzo@kernel.org>,
Saeed Mahameed <saeedm@nvidia.com>, Andrew Lunn <andrew@lunn.ch>,
Paolo Abeni <pabeni@redhat.com>
Subject: Re: [PATCH net-next v3 0/5] page_pool: recycle buffers
Date: Fri, 7 May 2021 11:23:28 +0800 [thread overview]
Message-ID: <75a332fa-74e4-7b7b-553e-3a1a6cb85dff@huawei.com> (raw)
In-Reply-To: <YJPn5t2mdZKC//dp@apalos.home>
On 2021/5/6 20:58, Ilias Apalodimas wrote:
>>>>
>>>
>>> Not really, the opposite is happening here. If the pp_recycle bit is set we
>>> will always call page_pool_return_skb_page(). If the page signature matches
>>> the 'magic' set by page pool we will always call xdp_return_skb_frame() will
>>> end up calling __page_pool_put_page(). If the refcnt is 1 we'll try
>>> to recycle the page. If it's not we'll release it from page_pool (releasing
>>> some internal references we keep) unmap the buffer and decrement the refcnt.
>>
>> Yes, I understood the above is what the page pool do now.
>>
>> But the question is who is still holding an extral reference to the page when
>> kfree_skb()? Perhaps a cloned and pskb_expand_head()'ed skb is holding an extral
>> reference to the same page? So why not just do a page_ref_dec() if the orginal skb
>> is freed first, and call __page_pool_put_page() when the cloned skb is freed later?
>> So that we can always reuse the recyclable page from a recyclable skb. This may
>> make the page_pool_destroy() process delays longer than before, I am supposed the
>> page_pool_destroy() delaying for cloned skb case does not really matters here.
>>
>> If the above works, I think the samiliar handling can be added to RX zerocopy if
>> the RX zerocopy also hold extral references to the recyclable page from a recyclable
>> skb too?
>>
>
> Right, this sounds doable, but I'll have to go back code it and see if it
> really makes sense. However I'd still prefer the support to go in as-is
> (including the struct xdp_mem_info in struct page, instead of a page_pool
> pointer).
>
> There's a couple of reasons for that. If we keep the struct xdp_mem_info we
> can in the future recycle different kind of buffers using __xdp_return().
> And this is a non intrusive change if we choose to store the page pool address
> directly in the future. It just affects the internal contract between the
> page_pool code and struct page. So it won't affect any drivers that already
> use the feature.
This patchset has embeded a signature field in "struct page", and xdp_mem_info
is stored in page_private(), which seems not considering the case for associating
the page pool with "struct page" directly yet? Is the page pool also stored in
page_private() and a different signature is used to indicate that?
I am not saying we have to do it in this patchset, but we have to consider it
while we are adding new signature field to "struct page", right?
> Regarding the page_ref_dec(), which as I said sounds doable, I'd prefer
> playing it safe for now and getting rid of the buffers that somehow ended up
> holding an extra reference. Once this gets approved we can go back and try to
> save the extra space. I hope I am not wrong but the changes required to
> support a few extra refcounts should not change the current patches much.
>
> Thanks for taking the time on this!
Thanks all invovled in the effort improving page pool too:)
> /Ilias
>
>>>
>>> [1] https://lore.kernel.org/netdev/154413868810.21735.572808840657728172.stgit@firesoul/
>>>
>>> Cheers
>>> /Ilias
>>>
>>> .
>>>
>>
>
> .
>
next prev parent reply other threads:[~2021-05-07 3:23 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-09 22:37 [PATCH net-next v3 0/5] page_pool: recycle buffers Matteo Croce
2021-04-09 22:37 ` [PATCH net-next v3 1/5] xdp: reduce size of struct xdp_mem_info Matteo Croce
2021-04-09 22:37 ` [PATCH net-next v3 2/5] mm: add a signature in struct page Matteo Croce
2021-04-10 15:48 ` Matthew Wilcox
2021-04-10 16:16 ` Ilias Apalodimas
2021-04-10 17:42 ` Shakeel Butt
2021-04-10 18:27 ` Ilias Apalodimas
2021-04-10 19:39 ` Matthew Wilcox
2021-04-11 10:05 ` Jesper Dangaard Brouer
2021-04-14 19:41 ` Jesper Dangaard Brouer
2021-04-14 20:09 ` Shakeel Butt
2021-04-14 20:51 ` Eric Dumazet
2021-04-19 5:12 ` Ilias Apalodimas
2021-04-19 14:57 ` Shakeel Butt
2021-04-19 15:43 ` Ilias Apalodimas
2021-04-19 16:21 ` Shakeel Butt
2021-04-19 18:41 ` Ilias Apalodimas
2021-04-19 11:22 ` Jesper Dangaard Brouer
2021-04-19 13:01 ` Matthew Wilcox
2021-04-20 8:10 ` Ilias Apalodimas
2021-04-09 22:37 ` [PATCH net-next v3 3/5] page_pool: Allow drivers to hint on SKB recycling Matteo Croce
2021-04-10 0:11 ` Ilias Apalodimas
2021-04-10 0:39 ` Matteo Croce
2021-04-09 22:38 ` [PATCH net-next v3 4/5] mvpp2: recycle buffers Matteo Croce
2021-04-09 22:38 ` [PATCH net-next v3 5/5] mvneta: " Matteo Croce
2021-04-29 8:27 ` [PATCH net-next v3 0/5] page_pool: " Yunsheng Lin
2021-04-29 18:51 ` Ilias Apalodimas
2021-04-30 3:01 ` Yunsheng Lin
2021-04-30 16:24 ` Ilias Apalodimas
2021-04-30 17:32 ` Ilias Apalodimas
2021-05-03 7:29 ` Jesper Dangaard Brouer
2021-05-06 12:34 ` Yunsheng Lin
2021-05-06 12:58 ` Ilias Apalodimas
2021-05-07 3:23 ` Yunsheng Lin [this message]
2021-05-07 7:06 ` Ilias Apalodimas
2021-05-07 8:28 ` Yunsheng Lin
2021-05-07 10:19 ` Jesper Dangaard Brouer
2021-05-07 11:31 ` Christoph Hellwig
2021-05-09 5:11 ` Shay Agroskin
2021-05-11 8:41 ` Ilias Apalodimas
2021-05-10 2:20 ` Yunsheng Lin
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