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>,
Will Deacon <will@kernel.org>,
Michel Lespinasse <walken@google.com>,
Fenghua Yu <fenghua.yu@intel.com>, Roman Gushchin <guro@fb.com>,
Hugh Dickins <hughd@google.com>, Peter Xu <peterx@redhat.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
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>,
Kevin Hao <haokexin@gmail.com>,
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: Thu, 6 May 2021 20:34:48 +0800 [thread overview]
Message-ID: <33b02220-cc50-f6b2-c436-f4ec041d6bc4@huawei.com> (raw)
In-Reply-To: <YIwvI5/ygBvZG5sy@apalos.home>
On 2021/5/1 0:24, Ilias Apalodimas wrote:
> [...]
>>>>
>>>> 1. skb frag page recycling do not need "struct xdp_rxq_info" or
>>>> "struct xdp_mem_info" to bond the relation between "struct page" and
>>>> "struct page_pool", which seems uncessary at this point if bonding
>>>> a "struct page_pool" pointer directly in "struct page" does not cause
>>>> space increasing.
>>>
>>> We can't do that. The reason we need those structs is that we rely on the
>>> existing XDP code, which already recycles it's buffers, to enable
>>> recycling. Since we allocate a page per packet when using page_pool for a
>>> driver , the same ideas apply to an SKB and XDP frame. We just recycle the
>>
>> I am not really familar with XDP here, but a packet from hw is either a
>> "struct xdp_frame/xdp_buff" for XDP or a "struct sk_buff" for TCP/IP stack,
>> a packet can not be both "struct xdp_frame/xdp_buff" and "struct sk_buff" at
>> the same time, right?
>>
>
> Yes, but the payload is irrelevant in both cases and that's what we use
> page_pool for. You can't use this patchset unless your driver usues
> build_skb(). So in both cases you just allocate memory for the payload and
I am not sure I understood why build_skb() matters here. If the head data of
a skb is a page frag and is from page pool, then it's page->signature should be
PP_SIGNATURE, otherwise it's page->signature is zero, so a recyclable skb does
not require it's head data being from a page pool, right?
> decide what the wrap the buffer with (XDP or SKB) later.
[...]
>>
>> I am not sure I understand what you meant by "free the skb", does it mean
>> that kfree_skb() is called to free the skb.
>
> Yes
>
>>
>> As my understanding, if the skb completely own the page(which means page_count()
>> == 1) when kfree_skb() is called, __page_pool_put_page() is called, otherwise
>> page_ref_dec() is called, which is exactly what page_pool_atomic_sub_if_positive()
>> try to handle it atomically.
>>
>
> 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?
>
> [1] https://lore.kernel.org/netdev/154413868810.21735.572808840657728172.stgit@firesoul/
>
> Cheers
> /Ilias
>
> .
>
next prev parent reply other threads:[~2021-05-06 12:34 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 [this message]
2021-05-06 12:58 ` Ilias Apalodimas
2021-05-07 3:23 ` Yunsheng Lin
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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