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Tue, 2 Jun 2026 22:41:41 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id Pw7/MCVcH2o1QwAAD6G6ig (envelope-from ); Tue, 02 Jun 2026 22:41:41 +0000 Date: Tue, 2 Jun 2026 23:41:40 +0100 From: Pedro Falcato To: Linus Torvalds , Askar Safin Cc: akpm@linux-foundation.org, axboe@kernel.dk, brauner@kernel.org, david@kernel.org, dhowells@redhat.com, hch@infradead.org, jack@suse.cz, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, miklos@szeredi.hu, netdev@vger.kernel.org, patches@lists.linux.dev, viro@zeniv.linux.org.uk, willy@infradead.org Subject: Re: [PATCH 0/3] vmsplice: make vmsplice a trivial wrapper for preadv2/pwritev2 Message-ID: References: <20260602211242.13870-1-safinaskar@gmail.com> Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Flag: NO X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.999]; MIME_GOOD(-0.10)[text/plain]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_TWELVE(0.00)[18]; FUZZY_RATELIMITED(0.00)[rspamd.com]; ARC_NA(0.00)[]; FREEMAIL_TO(0.00)[linux-foundation.org,gmail.com]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:email] X-Spam-Level: X-Spam-Score: -4.30 On Tue, Jun 02, 2026 at 03:06:07PM -0700, Linus Torvalds wrote: > On Tue, 2 Jun 2026 at 14:37, Pedro Falcato wrote: > > > > Well, that's most definitely part of my patch. Also, you cannot outright > > remove splice() functionality > > That isn't what Askar's patch ever did. > > You apparently didn't even read it. Well, I was replying to Askar's new idea to remove pagecache-to-pipe splice, which is what he suggested. And directly intersects with my sysctl-to-disable-splice patch. > Honestly, I think you are the one out of line here. > > Askar did something I suggested years ago, and didn't remove any functionality. > > It just changes vmsplice to be a copying model (one of the directions > already was). It doesn't change regular splice at all. > > And yes, it has the potential to be a visible behavior difference - if > some insane user uses vmsplice and then modifies the buffer > *afterwards*, then that would be semantically different between a > zero-copy and a normal copy. > > But that would be insane behavior, and was never really reliable > anyway even with zero-copy (ie subsequent writes to user space buffers > would potentially do COW breaking based purely on timing and memory > pressure etc, so anybody who relied on it being visible wasn't goign > to get it realiably anyway) > > Perhaps more importantly, it has the potential to change performance - > zero-copy *can* be a performance win, although typically it really > doesn't tend to be (looking up the page mapping is often slower than > copying). > > I would expect it to be very clear in trivial benchmarks that aren't > actually real loads. And probably not visible anywhere else. Yes, vmsplice() sucks, and we know it. Hopefully no one else will see the difference. I don't think we can say the same for splice(), though. > Trying to make it look like Askar is the problem is only making you look worse. To be clear, I don't think Askar is the (or a) problem. I'm glad he's contributing, and getting rid of bad kernel interfaces is always nice. I was just a little frustrated with a parallel splice-related-unscrew patch. (Askar, if I was too hostile, I do sincerely apologize.) -- Pedro