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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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: A585820003 X-Stat-Signature: rij8x716jbyc89jfmx7mqsxfpsmya9h1 X-HE-Tag: 1780440104-253671 X-HE-Meta: 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 /pyymIZQ 82vdpjJe5fkKVwLWN6pseqp+isBrDI/MgAvaDEtwg0ww2M/FOdxRPcSqqlU2mCMlfcujz71W2d6weY7gGa/IGsc4F+fXyBQYCgmsTcCFOJ6RFzBjdBsekjeMGBdcEzfEXHlVEng8E6stNvIQqBbUDyEXjkddCfBreF3nU4wRR2sMtkvmEAHAys+d561IDBiwjZmnTPOujt+EbT8X3NUnXpjW8CAFOz0G4jA81OnDaQwY/1EzqVGJG408lppvf33fGMJlHZ2jSJ6woWs0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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