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Thu, 25 Jun 2026 01:54:07 -0700 (PDT) From: Askar Safin To: avagin@gmail.com Cc: akpm@linux-foundation.org, alexander@mihalicyn.com, axboe@kernel.dk, bernd@bsbernd.com, brauner@kernel.org, criu@lists.linux.dev, david@kernel.org, dhowells@redhat.com, fuse-devel@lists.linux.dev, hch@infradead.org, jack@suse.cz, joannelkoong@gmail.com, 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, pfalcato@suse.de, rostedt@goodmis.org, safinaskar@gmail.com, torvalds@linux-foundation.org, val@packett.cool, viro@zeniv.linux.org.uk, willy@infradead.org Subject: Re: [PATCH 0/3] vmsplice: make vmsplice a trivial wrapper for preadv2/pwritev2 Date: Thu, 25 Jun 2026 11:53:57 +0300 Message-ID: <20260625085401.3787887-1-safinaskar@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: References: Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Andrei Vagin : > On Wed, Jun 24, 2026 at 12:12 AM Askar Safin wrote: > > Does CRIU actually rely on ability to do SPLICE_F_NONBLOCK vmsplice into > > named fifos? Or this is merely a test? > > Yes, it does. I. e. CRIU relies on that named fifo behavior? Okay, I just sent v2 version of my fixes. The patchset contains fix for named fifos. Please, test that this fixes that named fifo problem. > I already explained that this isn't just a perfomance degradation, it > actually breaks the pre-dump mechanism in CRIU. vmsplice is invoked from > our parasite code within the context of a user process, where execution > speed is critical. A heavy performance penalty completely invalidates > the pre-dump logic, making the feature useless. This is very unfortunate. But I still want to remove vmsplice. > At a minimum, we may need to consider a deprecation plan where vmsplice > with SPLICE_F_GIFT triggers a warning for a few releases before these > changes are applied. Alternatively, we could introduce the proposed > behavior alongside a sysctl to fall back to the old behavior and explicitly > state that this fallback path will be completely deprecated in a future kernel > version. My patches change not only SPLICE_F_GIFT behavior, but also vmsplice behavior in general. Let other developers decide what to do (i. e. do nothing, remove vmsplice now or implement some deprecation scheme). -- Askar Safin