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Wed, 05 Mar 2025 16:46:52 -0800 (PST) Date: Wed, 5 Mar 2025 16:46:51 -0800 From: Cong Wang To: Matthew Wilcox Cc: Hannes Reinecke , Vlastimil Babka , Hannes Reinecke , Boris Pismenny , John Fastabend , Jakub Kicinski , Sagi Grimberg , "linux-nvme@lists.infradead.org" , "linux-block@vger.kernel.org" , linux-mm@kvack.org, Harry Yoo , "netdev@vger.kernel.org" Subject: Re: Networking people smell funny and make poor life choices Message-ID: References: <27111897-0b36-4d8c-8be9-4f8bdbae88b7@suse.cz> <7439cb2f-6a97-494b-aa10-e9bebb218b58@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: bfmdbahspg94j6ckw67bz6jtap9nmn3m X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 49B2F100005 X-Rspam-User: X-HE-Tag: 1741222014-256301 X-HE-Meta: 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 V+ewkPxl 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.121953, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.