netdev - Networking people smell funny and make poor life choices

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Message-ID: <Z8iTzPRieLB7Ee-9@casper.infradead.org>
Date: Wed, 5 Mar 2025 18:11:24 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Hannes Reinecke <hare@...e.de>
Cc: 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: Networking people smell funny and make poor life choices

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.