From: Pavel Begunkov <asml.silence@gmail.com>
To: Mina Almasry <almasrymina@google.com>, David Wei <dw@davidwei.uk>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org, linux-alpha@vger.kernel.org,
linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org,
sparclinux@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
linux-arch@vger.kernel.org, bpf@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org,
dri-devel@lists.freedesktop.org,
"David S. Miller" <davem@davemloft.net>,
"Eric Dumazet" <edumazet@google.com>,
"Jakub Kicinski" <kuba@kernel.org>,
"Paolo Abeni" <pabeni@redhat.com>,
"Jonathan Corbet" <corbet@lwn.net>,
"Richard Henderson" <richard.henderson@linaro.org>,
"Ivan Kokshaysky" <ink@jurassic.park.msu.ru>,
"Matt Turner" <mattst88@gmail.com>,
"Thomas Bogendoerfer" <tsbogend@alpha.franken.de>,
"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
"Helge Deller" <deller@gmx.de>,
"Andreas Larsson" <andreas@gaisler.com>,
"Jesper Dangaard Brouer" <hawk@kernel.org>,
"Ilias Apalodimas" <ilias.apalodimas@linaro.org>,
"Steven Rostedt" <rostedt@goodmis.org>,
"Masami Hiramatsu" <mhiramat@kernel.org>,
"Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>,
"Arnd Bergmann" <arnd@arndb.de>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Martin KaFai Lau" <martin.lau@linux.dev>,
"Eduard Zingerman" <eddyz87@gmail.com>,
"Song Liu" <song@kernel.org>,
"Yonghong Song" <yonghong.song@linux.dev>,
"John Fastabend" <john.fastabend@gmail.com>,
"KP Singh" <kpsingh@kernel.org>,
"Stanislav Fomichev" <sdf@google.com>,
"Hao Luo" <haoluo@google.com>, "Jiri Olsa" <jolsa@kernel.org>,
"David Ahern" <dsahern@kernel.org>,
"Willem de Bruijn" <willemdebruijn.kernel@gmail.com>,
"Shuah Khan" <shuah@kernel.org>,
"Sumit Semwal" <sumit.semwal@linaro.org>,
"Christian König" <christian.koenig@amd.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Yunsheng Lin" <linyunsheng@huawei.com>,
"Shailend Chand" <shailend@google.com>,
"Harshitha Ramamurthy" <hramamurthy@google.com>,
"Jeroen de Borst" <jeroendb@google.com>,
"Praveen Kaligineedi" <pkaligineedi@google.com>,
shakeel.butt@linux.dev
Subject: Re: [RFC PATCH net-next v6 02/15] net: page_pool: create hooks for custom page providers
Date: Wed, 6 Mar 2024 14:29:56 +0000 [thread overview]
Message-ID: <417f293a-848e-4eb2-b690-c8696079b452@gmail.com> (raw)
In-Reply-To: <CAHS8izM5O39mnTQ8mhcQE75amDT4G-3vcgozzjcYsAdd_-he1g@mail.gmail.com>
On 3/5/24 22:36, Mina Almasry wrote:
> On Tue, Mar 5, 2024 at 1:55 PM David Wei <dw@davidwei.uk> wrote:
>>
>> On 2024-03-04 18:01, Mina Almasry wrote:
>>> +struct memory_provider_ops {
>>> + int (*init)(struct page_pool *pool);
>>> + void (*destroy)(struct page_pool *pool);
>>> + struct page *(*alloc_pages)(struct page_pool *pool, gfp_t gfp);
>>> + bool (*release_page)(struct page_pool *pool, struct page *page);
>>
>> For ZC Rx we added a scrub() function to memory_provider_ops that is
>> called from page_pool_scrub(). Does TCP devmem not custom behaviour
>> waiting for all netmem_refs to return before destroying the page pool?
>> What happens if e.g. application crashes?
>
> (sorry for the long reply, but he refcounting is pretty complicated to
> explain and I feel like we need to agree on how things currently work)
>
> Yeah, the addition of the page_pool_scrub() function is a bit of a
> head scratcher for me. Here is how the (complicated) refcounting works
> for devmem TCP (assuming the driver is not doing its own recycling
> logic which complicates things further):
>
> 1. When a netmem_ref is allocated by the page_pool (from dmabuf or
> page), the netmem_get_pp_ref_count_ref()==1 and belongs to the page
> pool as long as the netmem is waiting in the pool for driver
> allocation.
>
> 2. When a netmem is allocated by the driver, no refcounting is
> changed, but the ownership of the netmem_get_pp_ref_count_ref() is
> implicitly transferred from the page pool to the driver. i.e. the ref
> now belongs to the driver until an skb is formed.
>
> 3. When the driver forms an skb using skb_rx_add_frag_netmem(), no
> refcounting is changed, but the ownership of the
> netmem_get_pp_ref_count_ref() is transferred from the driver to the
> TCP stack.
>
> 4. When the TCP stack hands the skb to the application, the TCP stack
> obtains an additional refcount, so netmem_get_pp_ref_count_ref()==2,
> and frees the skb using skb_frag_unref(), which drops the
> netmem_get_pp_ref_count_ref()==1.
>
> 5. When the user is done with the skb, the user calls the
> DEVMEM_DONTNEED setsockopt which calls napi_pp_put_netmem() which
> recycles the netmem back to the page pool. This doesn't modify any
> refcounting, but the refcount ownership transfers from the userspace
> back to the page pool, and we're back at step 1.
>
> So all in all netmem can belong either to (a) the page pool, or (b)
> the driver, or (c) the TCP stack, or (d) the application depending on
> where exactly it is in the RX path.
>
> When an application running devmem TCP crashes, the netmem that belong
> to the page pool or driver are not touched, because the page pool is
> not tied to the application in our case really. However, the TCP stack
> notices the devmem socket of the application close, and when it does,
> the TCP stack will:
>
> 1. Free all the skbs in the sockets receive queue. This is not custom
> behavior for devmem TCP, it's just standard for TCP to free all skbs
> waiting to be received by the application.
> 2. The TCP stack will free references that belong to the application.
> Since the application crashed, it will not call the DEVMEM_DONTNEED
> setsockopt, so we need to free those on behalf of the application.
> This is done in this diff:
>
> @@ -2498,6 +2498,15 @@ static void tcp_md5sig_info_free_rcu(struct
> rcu_head *head)
> void tcp_v4_destroy_sock(struct sock *sk)
> {
> struct tcp_sock *tp = tcp_sk(sk);
> + __maybe_unused unsigned long index;
> + __maybe_unused void *netmem;
> +
> +#ifdef CONFIG_PAGE_POOL
> + xa_for_each(&sk->sk_user_frags, index, netmem)
> + WARN_ON_ONCE(!napi_pp_put_page((__force netmem_ref)netmem, false));
> +#endif
> +
> + xa_destroy(&sk->sk_user_frags);
>
> trace_tcp_destroy_sock(sk);
>
> To be honest, I think it makes sense for the TCP stack to be
> responsible for putting the references that belong to it and the
> application. To me, it does not make much sense for the page pool to
> be responsible for putting the reference that belongs to the TCP stack
> or driver via a page_pool_scrub() function, as those references do not
> belong to the page pool really. I'm not sure why there is a diff
> between our use cases here because I'm not an io_uring expert. Why do
> you need to scrub all the references on page pool destruction? Don't
> these belong to non-page pool components like io_uring stack or TCP
> stack ol otherwise?
That one is about cleaning buffers that are in b/w 4 and 5, i.e.
owned by the user, which devmem does at sock destruction. io_uring
could get by without scrub, dropping user refs while unregistering
ifq, but then it'd need to wait for all requests to finish so there
is no step 4 in the meantime. Might change, can be useful, but it
was much easier to hook into the pp release loop.
Another concern is who and when can reset ifq / kill pp outside
of io_uring/devmem. I assume it can happen on a whim, which is
hard to handle gracefully.
--
Pavel Begunkov
next prev parent reply other threads:[~2024-03-06 14:30 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-05 2:01 [RFC PATCH net-next v6 00/15] Device Memory TCP Mina Almasry
2024-03-05 2:01 ` [RFC PATCH net-next v6 01/15] queue_api: define queue api Mina Almasry
2024-03-08 1:30 ` Jakub Kicinski
2024-03-08 2:08 ` Mina Almasry
2024-03-08 3:36 ` Jakub Kicinski
2024-03-08 23:47 ` David Wei
2024-03-09 0:27 ` Mina Almasry
2024-03-11 1:12 ` David Ahern
2024-03-05 2:01 ` [RFC PATCH net-next v6 02/15] net: page_pool: create hooks for custom page providers Mina Almasry
2024-03-05 21:54 ` David Wei
2024-03-05 22:36 ` Mina Almasry
2024-03-06 14:29 ` Pavel Begunkov [this message]
2024-03-06 17:04 ` Mina Almasry
2024-03-06 19:12 ` Pavel Begunkov
2024-03-06 21:59 ` Mina Almasry
2024-03-07 14:25 ` Pavel Begunkov
2024-03-08 4:57 ` David Wei
2024-03-08 19:53 ` Mina Almasry
2024-03-18 2:02 ` Christoph Hellwig
2024-03-18 2:49 ` David Wei
2024-03-18 23:22 ` Christoph Hellwig
2024-03-22 17:40 ` Mina Almasry
2024-03-22 23:19 ` Jakub Kicinski
2024-03-24 23:35 ` Christoph Hellwig
2024-03-24 23:35 ` Christoph Hellwig
2024-03-22 17:54 ` Mina Almasry
2024-03-24 23:37 ` Christoph Hellwig
2024-03-26 20:19 ` Mina Almasry
2024-03-28 7:31 ` Christoph Hellwig
2024-04-01 19:22 ` Mina Almasry
2024-04-08 15:34 ` Cong Wang
2024-03-05 2:01 ` [RFC PATCH net-next v6 03/15] net: page_pool: factor out page_pool recycle check Mina Almasry
2024-03-05 12:55 ` Yunsheng Lin
2024-03-05 2:01 ` [RFC PATCH net-next v6 04/15] net: netdev netlink api to bind dma-buf to a net device Mina Almasry
2024-03-05 2:01 ` [RFC PATCH net-next v6 05/15] netdev: support binding dma-buf to netdevice Mina Almasry
2024-03-05 9:04 ` Arnd Bergmann
2024-03-05 20:00 ` Mina Almasry
2024-03-05 21:42 ` Arnd Bergmann
2024-03-05 12:55 ` Yunsheng Lin
2024-03-05 21:17 ` Mina Almasry
2024-03-06 12:38 ` Yunsheng Lin
2024-03-06 22:10 ` Mina Almasry
2024-03-07 12:15 ` Yunsheng Lin
2024-03-08 3:58 ` Jakub Kicinski
2024-03-05 2:01 ` [RFC PATCH net-next v6 06/15] netdev: netdevice devmem allocator Mina Almasry
2024-03-05 2:01 ` [RFC PATCH net-next v6 07/15] page_pool: convert to use netmem Mina Almasry
2024-03-05 21:30 ` Mina Almasry
2024-03-05 2:01 ` [RFC PATCH net-next v6 08/15] page_pool: devmem support Mina Almasry
2024-03-05 21:42 ` Mina Almasry
2024-03-05 2:01 ` [RFC PATCH net-next v6 09/15] memory-provider: dmabuf devmem memory provider Mina Almasry
2024-03-06 2:28 ` David Wei
2024-03-06 2:42 ` Mina Almasry
2024-03-06 2:46 ` David Wei
2024-03-06 2:54 ` Mina Almasry
2024-03-06 14:58 ` Pavel Begunkov
2024-03-06 16:51 ` Mina Almasry
2024-03-05 2:01 ` [RFC PATCH net-next v6 10/15] net: support non paged skb frags Mina Almasry
2024-03-05 2:01 ` [RFC PATCH net-next v6 11/15] net: add support for skbs with unreadable frags Mina Almasry
2024-03-05 2:01 ` [RFC PATCH net-next v6 12/15] tcp: RX path for devmem TCP Mina Almasry
2024-03-05 8:41 ` Arnd Bergmann
2024-03-05 19:22 ` Mina Almasry
2024-03-05 19:39 ` Arnd Bergmann
2024-03-05 2:01 ` [RFC PATCH net-next v6 13/15] net: add SO_DEVMEM_DONTNEED setsockopt to release RX frags Mina Almasry
2024-03-05 2:01 ` [RFC PATCH net-next v6 14/15] net: add devmem TCP documentation Mina Almasry
2024-03-08 1:52 ` Jakub Kicinski
2024-03-05 2:01 ` [RFC PATCH net-next v6 15/15] selftests: add ncdevmem, netcat for devmem TCP Mina Almasry
2024-03-05 7:16 ` [RFC PATCH net-next v6 07/15] page_pool: convert to use netmem David Howells
2024-03-05 12:54 ` [RFC PATCH net-next v6 00/15] Device Memory TCP Yunsheng Lin
2024-03-05 19:38 ` Mina Almasry
2024-03-06 12:37 ` Yunsheng Lin
2024-03-26 0:28 ` Mina Almasry
2024-03-26 12:47 ` Yunsheng Lin
2024-03-26 20:14 ` Mina Almasry
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=417f293a-848e-4eb2-b690-c8696079b452@gmail.com \
--to=asml.silence@gmail.com \
--cc=James.Bottomley@hansenpartnership.com \
--cc=almasrymina@google.com \
--cc=andreas@gaisler.com \
--cc=andrii@kernel.org \
--cc=arnd@arndb.de \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=christian.koenig@amd.com \
--cc=corbet@lwn.net \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=deller@gmx.de \
--cc=dri-devel@lists.freedesktop.org \
--cc=dsahern@kernel.org \
--cc=dw@davidwei.uk \
--cc=eddyz87@gmail.com \
--cc=edumazet@google.com \
--cc=haoluo@google.com \
--cc=hawk@kernel.org \
--cc=hramamurthy@google.com \
--cc=ilias.apalodimas@linaro.org \
--cc=ink@jurassic.park.msu.ru \
--cc=jeroendb@google.com \
--cc=jgg@ziepe.ca \
--cc=john.fastabend@gmail.com \
--cc=jolsa@kernel.org \
--cc=kpsingh@kernel.org \
--cc=kuba@kernel.org \
--cc=linux-alpha@vger.kernel.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=linux-media@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=linux-parisc@vger.kernel.org \
--cc=linux-trace-kernel@vger.kernel.org \
--cc=linyunsheng@huawei.com \
--cc=martin.lau@linux.dev \
--cc=mathieu.desnoyers@efficios.com \
--cc=mattst88@gmail.com \
--cc=mhiramat@kernel.org \
--cc=netdev@vger.kernel.org \
--cc=pabeni@redhat.com \
--cc=pkaligineedi@google.com \
--cc=richard.henderson@linaro.org \
--cc=rostedt@goodmis.org \
--cc=sdf@google.com \
--cc=shailend@google.com \
--cc=shakeel.butt@linux.dev \
--cc=shuah@kernel.org \
--cc=song@kernel.org \
--cc=sparclinux@vger.kernel.org \
--cc=sumit.semwal@linaro.org \
--cc=tsbogend@alpha.franken.de \
--cc=willemdebruijn.kernel@gmail.com \
--cc=yonghong.song@linux.dev \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).