netdev - Re: [PATCH v2 1/2] udp: UDP socket send queue repair

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Message-ID: <YRviPJwrnuh9Nn35@gmail.com>
Date:   Tue, 17 Aug 2021 09:22:20 -0700
From:   "avagin@...il.com" <avagin@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     'Bui Quang Minh' <minhquangbui99@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "yoshfuji@...ux-ipv6.org" <yoshfuji@...ux-ipv6.org>,
        "dsahern@...nel.org" <dsahern@...nel.org>,
        "willemb@...gle.com" <willemb@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "alexander@...alicyn.com" <alexander@...alicyn.com>,
        "lesedorucalin01@...il.com" <lesedorucalin01@...il.com>
Subject: Re: [PATCH v2 1/2] udp: UDP socket send queue repair

On Fri, Aug 13, 2021 at 01:00:12PM +0000, David Laight wrote:
> From: Bui Quang Minh
> > Sent: 13 August 2021 12:08
> ...
> > 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.
> 
> Patient: It hurts if I do xxx.
> Doctor: Don't do xxx then.
> 
> It has to be more efficient to buffer partial UDP packets
> in userspace and only send when all the packet is available.

You are right. It can be more efficient, but we don't have controls over
user-space processes, and they can do whatever the kernel allows them to
do.

> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
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