netdev - Re: [PATCH net-next v3 10/18] nvme/host: Use sendmsg(MSG_SPLICE

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Date: Thu, 29 Jun 2023 17:49:46 +0300
From: Sagi Grimberg <sagi@...mberg.me>
To: Aurelien Aptel <aaptel@...dia.com>, David Howells <dhowells@...hat.com>,
 netdev@...r.kernel.org
Cc: Alexander Duyck <alexander.duyck@...il.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 David Ahern <dsahern@...nel.org>, Matthew Wilcox <willy@...radead.org>,
 Jens Axboe <axboe@...nel.dk>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Willem de Bruijn <willemb@...gle.com>,
 Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
 Christoph Hellwig <hch@....de>, Chaitanya Kulkarni <kch@...dia.com>,
 linux-nvme@...ts.infradead.org
Subject: Re: [PATCH net-next v3 10/18] nvme/host: Use
 sendmsg(MSG_SPLICE_PAGES) rather then sendpage

> Hi David,
> 
> David Howells <dhowells@...hat.com> writes:
>> When transmitting data, call down into TCP using a single sendmsg with
>> MSG_SPLICE_PAGES to indicate that content should be spliced rather than
>> performing several sendmsg and sendpage calls to transmit header, data
>> pages and trailer.
> 
> This series makes my kernel crash.
> 
>  From the current net-next main branch:
> 
> commit 9ae440b8fdd6772b6c007fa3d3766530a09c9045 (HEAD)
> Merge: b545a13ca9b2 b848b26c6672
> Author: Jakub Kicinski <kuba@...nel.org>
> Date:   Sat Jun 24 15:50:21 2023 -0700
> 
>      Merge branch 'splice-net-switch-over-users-of-sendpage-and-remove-it'
> 
> 
> Steps to reproduce:
> 
> * connect a remote nvme null block device (nvmet) with 1 IO queue to keep
>    things simple
> * open /dev/nvme0n1 with O_RDWR|O_DIRECT|O_SYNC
> * write() a 8k buffer or 4k buffer

Most likely this also reproduces with blktests?
https://github.com/osandov/blktests

simple way to check is to run:
nvme_trtype=tcp ./check nvme

This runs nvme tests over nvme-tcp.

No need for network, disk or anything. It runs
both nvme and nvmet over the lo device..