netdev - Re: Networking people smell funny and make poor life choices

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Message-ID: <Z8jwe7dFXVEI9fT1@pop-os.localdomain>
Date: Wed, 5 Mar 2025 16:46:51 -0800
From: Cong Wang <xiyou.wangcong@...il.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Hannes Reinecke <hare@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
	Hannes Reinecke <hare@...e.com>, Boris Pismenny <borisp@...dia.com>,
	John Fastabend <john.fastabend@...il.com>,
	Jakub Kicinski <kuba@...nel.org>, Sagi Grimberg <sagi@...mberg.me>,
	"linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	linux-mm@...ck.org, Harry Yoo <harry.yoo@...cle.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Networking people smell funny and make poor life choices

On Wed, Mar 05, 2025 at 06:11:24PM +0000, Matthew Wilcox wrote:
> On Wed, Mar 05, 2025 at 12:43:02PM +0100, Hannes Reinecke wrote:
> > Oh, sure. But what annoys me: why do we have to care?
> > 
> > When doing I/O _all_ data is stuffed into bvecs via
> > bio_add_page(), and after that information about the
> > origin is lost; any iteration on the bio will be a bvec
> > iteration.
> > Previously we could just do a bvec iteration, get a reference
> > for each page, and start processing.
> > Now suddenly the caller has to check if it's a slab page and don't
> > get a reference for that. Not only that, he also has to remember
> > to _not_ drop the reference when he's done.
> > And, of course, tracing get_page() and the corresponding put_page()
> > calls through all the layers.
> 
> Networking needs to follow block's lead and STOP GETTING REFCOUNTS ON
> PAGES.  That will speed up networking (eliminates two atomic operations per
> page).  And of course, it will eliminate this hack in the MM.  I think
> we do need to put this hack into the MM for now, but it needs to go away
> again as quickly as possible.
> 
> What worries me is that nobody in networking has replied to this thread
> yet.  Do they not care?  Let's see if a subject line change will help
> with that.

Since it triggered a kernel crash, I am pretty sure people care. How
about sending out a patch to get more attentions?

I am not sure what patterns here you are suggesting to change w.r.t page
refcount, but at least using AI copilot or whatever automation tool should
be very handy.

Thanks.