LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Bui Quang Minh <minhquangbui99@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	David Miller <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
	David Ahern <dsahern@kernel.org>,
	Willem de Bruijn <willemb@google.com>,
	Paolo Abeni <pabeni@redhat.com>, Andrei Vagin <avagin@gmail.com>,
	alexander@mihalicyn.com,
	Lese Doru Calin <lesedorucalin01@gmail.com>
Subject: Re: [PATCH v2 1/2] udp: UDP socket send queue repair
Date: Mon, 16 Aug 2021 07:35:40 -0700	[thread overview]
Message-ID: <CAF=yD-+077uFihRAB0L5xr4pNLFAEnxnoNcCinVE0qt57_6Kwg@mail.gmail.com> (raw)
In-Reply-To: <3f861c1d-bd33-f074-8ef3-eede9bff73c1@gmail.com>

On Fri, Aug 13, 2021 at 4:52 AM Bui Quang Minh <minhquangbui99@gmail.com> wrote:
>
>
>
> On 8/12/2021 10:51 PM, Eric Dumazet wrote:
> >
> >
> > On 8/12/21 3:46 PM, Bui Quang Minh wrote:
> >>
> >>
> >> On 8/11/2021 11:14 PM, Eric Dumazet wrote:
> >>>
> >>>
> >>> On 8/11/21 5:45 PM, Bui Quang Minh wrote:
> >>>> In this patch, I implement UDP_REPAIR sockoption and a new path in
> >>>> udp_recvmsg for dumping the corked packet in UDP socket's send queue.
> >>>>
> >>>> A userspace program can use recvmsg syscall to get the packet's data and
> >>>> the msg_name information of the packet. Currently, other related
> >>>> information in inet_cork that are set in cmsg are not dumped.
> >>>>
> >>>> While working on this, I was aware of Lese Doru Calin's patch and got some
> >>>> ideas from it.
> >>>
> >>>
> >>> What is the use case for this feature, adding a test in UDP fast path ?
> >>
> >> This feature is used to help CRIU to dump CORKed UDP packet in send queue. I'm sorry for being not aware of the performance perspective here.
> >
> > UDP is not reliable.
> >
> > I find a bit strange we add so many lines of code
> > for a feature trying very hard to to drop _one_ packet.
> >
> > I think a much better changelog would be welcomed.
>
> The reason we want to dump the packet in send queue is to make to state of the
> application consistent. The scenario is that when an application sends UDP
> packets via UDP_CORK socket or with MSG_MORE, CRIU comes and checkpoints the
> application. If we drop the data in send queue, when application restores, it
> sends some more data then turns off the cork and actually sends a packet. The
> receiving side may get that packet but it's unusual that the first part of that
> packet is missing because we drop it. So we try to solve this problem with some
> help from the Linux kernel.

Instead of checkpointing the state, how about making the kernel drop
the next packet.

For instance by setting up->pending to something else than AF_UNSPEC,
AF_INET, AF_INET6 from a new setsockopt and testing for this case in
the udp_sendmsg up->pending slowpath.

udp_sendmsg already calls udp_v6_flush_pending_frames on error when
appending to a pending packet, so returning an error on the next call
after restore and have that imply a flush is acceptable. I would
introduce a new error code.

The state can perhaps be inferred in other ways, e.g., from
up->pending && !up->len or up->pending && !skb_peek_tail(queue). But
an explicit up->pending mode will be easier to grasp.

  parent reply	other threads:[~2021-08-16 14:36 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-11 15:45 Bui Quang Minh
2021-08-11 16:14 ` Eric Dumazet
2021-08-12 13:46   ` Bui Quang Minh
2021-08-12 15:51     ` Eric Dumazet
2021-08-13 11:08       ` Bui Quang Minh
2021-08-13 13:00         ` David Laight
2021-08-17 16:22           ` avagin
2021-08-16 14:35         ` Willem de Bruijn [this message]
2021-08-16 14:38 ` Willem de Bruijn

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='CAF=yD-+077uFihRAB0L5xr4pNLFAEnxnoNcCinVE0qt57_6Kwg@mail.gmail.com' \
    --to=willemdebruijn.kernel@gmail.com \
    --cc=alexander@mihalicyn.com \
    --cc=avagin@gmail.com \
    --cc=davem@davemloft.net \
    --cc=dsahern@kernel.org \
    --cc=eric.dumazet@gmail.com \
    --cc=kuba@kernel.org \
    --cc=lesedorucalin01@gmail.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=minhquangbui99@gmail.com \
    --cc=netdev@vger.kernel.org \
    --cc=pabeni@redhat.com \
    --cc=willemb@google.com \
    --cc=yoshfuji@linux-ipv6.org \
    --subject='Re: [PATCH v2 1/2] udp: UDP socket send queue repair' \
    /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

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).