From: Jon Maloy <jmaloy@redhat.com>
To: Menglong Dong <menglong8.dong@gmail.com>,
Jason Xing <kerneljasonxing@gmail.com>,
Eric Dumazet <edumazet@google.com>
Cc: netdev@vger.kernel.org, davem@davemloft.net, kuba@kernel.org,
passt-dev@passt.top, sbrivio@redhat.com, lvivier@redhat.com,
dgibson@redhat.com, eric.dumazet@gmail.com,
dongmenglong.8@bytedance.com
Subject: Re: [net-next 2/2] tcp: correct handling of extreme menory squeeze
Date: Mon, 8 Apr 2024 07:01:22 -0400 [thread overview]
Message-ID: <f0819d6d-338a-8441-d12a-771dbfd9028a@redhat.com> (raw)
In-Reply-To: <CADxym3ZfC5WF7C2B8oYq=38rsLnQ-DOfvhH3iSk6+L0g2=XWDQ@mail.gmail.com>
On 2024-04-07 03:51, Menglong Dong wrote:
> On Sun, Apr 7, 2024 at 2:52 PM Jason Xing <kerneljasonxing@gmail.com> wrote:
>> On Sun, Apr 7, 2024 at 2:38 AM Eric Dumazet <edumazet@google.com> wrote:
[...]
>>>> [5201<->54494]: tcp_recvmsg_locked(<-) returning -11 bytes, window now: 250164, qlen: 0
>>>>
>>>> We can see that although we are adverising a window size of zero,
>>>> tp->rcv_wnd is not updated accordingly. This leads to a discrepancy
>>>> between this side's and the peer's view of the current window size.
>>>> - The peer thinks the window is zero, and stops sending.
> Hi!
>
> In my original logic, the client will send a zero-window
> ack when it drops the skb because it is out of the
> memory. And the peer SHOULD keep retrans the dropped
> packet.
>
> Does the peer do the transmission in this case? The receive
> window of the peer SHOULD recover once the
> retransmission is successful.
The "peer" is this case is our user-space protocol splicer, emulating
the behavior of of the remote end socket.
At a first glance, it looks like it is *not* performing any retransmits
at all when it sees a zero window at the receiver, so this might indeed
be the problem.
I will be out of office today, but I will test this later this week.
///jon
>
>>>> - This side ends up in a cycle where it repeatedly caclulates a new
>>>> window size it finds too small to advertise.
> Yeah, the zero-window suppressed the sending of ack in
> __tcp_cleanup_rbuf, which I wasn't aware of.
>
> The ack will recover the receive window of the peer. Does
> it make the peer retrans the dropped data immediately?
> In my opinion, the peer still needs to retrans the dropped
> packet until the retransmission timer timeout. Isn't it?
>
> If it is, maybe we can do the retransmission immediately
> if we are in zero-window from a window-shrink, which can
> make the recovery faster.
>
> [......]
>>> Any particular reason to not cc Menglong Dong ?
>>> (I just did)
>> He is not working at Tencent any more. Let me CC here one more time.
> Thanks for CC the new email of mine, it's very kind of you,
> xing :/
>
next prev parent reply other threads:[~2024-04-08 11:01 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-06 18:21 [net-next 0/2] tcp: add support for SO_PEEK_OFF socket option jmaloy
2024-04-06 18:21 ` [net-next 1/2] " jmaloy
2024-04-08 9:46 ` Eric Dumazet
2024-04-06 18:21 ` [net-next 2/2] tcp: correct handling of extreme menory squeeze jmaloy
2024-04-06 16:37 ` Eric Dumazet
2024-04-07 4:52 ` Jason Xing
2024-04-07 5:51 ` Menglong Dong
2024-04-08 11:01 ` Jon Maloy [this message]
2024-04-08 8:03 ` Eric Dumazet
2024-04-08 11:13 ` Jon Maloy
-- strict thread matches above, loose matches on Subject: below --
2024-04-03 22:58 [net-next 0/2] tcp: add support for SO_PEEK_OFF socket option Jon Maloy
2024-04-03 22:58 ` [net-next 2/2] tcp: correct handling of extreme menory squeeze Jon Maloy
2024-04-05 17:55 ` Stefano Brivio
2024-04-05 19:37 ` Jon Maloy
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=f0819d6d-338a-8441-d12a-771dbfd9028a@redhat.com \
--to=jmaloy@redhat.com \
--cc=davem@davemloft.net \
--cc=dgibson@redhat.com \
--cc=dongmenglong.8@bytedance.com \
--cc=edumazet@google.com \
--cc=eric.dumazet@gmail.com \
--cc=kerneljasonxing@gmail.com \
--cc=kuba@kernel.org \
--cc=lvivier@redhat.com \
--cc=menglong8.dong@gmail.com \
--cc=netdev@vger.kernel.org \
--cc=passt-dev@passt.top \
--cc=sbrivio@redhat.com \
/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.
Code repositories for project(s) associated with this public inbox
https://passt.top/passt
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 IMAP folder(s).