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Thu, 25 Jun 2026 01:54:08 -0700 (PDT) Received: from localhost ([212.73.77.104]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-46c1ee018e8sm15530598f8f.11.2026.06.25.01.54.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); 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: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: B68F5180002 X-Stat-Signature: 9h71f88wd5xnkorpgfdy163rk5gctpyt X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1782377649-756988 X-HE-Meta: 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 vlidhnGQ 17H881zEJNOZmPYpRgeYZ7DGg1nGgDad/cq00BZSsAvA0QMccA7y5RKVcWvCm95tEc5fMrp2WByqwmnDXoPPwl+1/j0qMfc3Xh7CdYZNRF9bYDTWYQEAnoWP3bzHoFIw8lrQwh3kdgr2EoaX0GP5lmOtouS0DHy0tDp6m+OutoLiAljwyU5/G68c/JJLRiLc8S+Vvgv3lltN2RSIVsfMHgzypv7WS1BjZ98XS57npzQoyBQWwJvpMQX+kJSQe9xXYnWOuG8LiNoryVAiuQSLSx5rtZ66Ij8O6nH28cco+CTdzAEmVpab3V4XvjpAkHz9iAPjJxuVpqiREw0qZiTNN1KUeDFm9CS4MZnkX3/iUzcmiLxVb8l6JmwYY+ZKfH9ivQny9h4rJ+Wktq6eF56Zy4m/WM7gfQ9VVJpB3vJT1Sawpez+gzeTrDqjSqWCA835MXz8tTKhhLs4EtUU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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