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Wed, 28 Oct 2026 10:16:59 -0400 (EDT) Date: Wed, 28 Oct 2026 14:16:58 +0000 From: Kiryl Shutsemau To: Peter Zijlstra Cc: Muchun Song , "David Hildenbrand (Arm)" , Andrew Morton , Matthew Wilcox , Usama Arif , Frank van der Linden , Oscar Salvador , Mike Rapoport , Vlastimil Babka , Lorenzo Stoakes , Zi Yan , Baoquan He , Michal Hocko , Johannes Weiner , Jonathan Corbet , Huacai Chen , WANG Xuerui , Palmer Dabbelt , Paul Walmsley , Albert Ou , Alexandre Ghiti , kernel-team@meta.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, Dave Hansen , Andy Lutomirski Subject: Re: [PATCHv7 13/18] mm: Drop fake head checks Message-ID: References: <070DDE5C-2183-4A8B-AC2D-891CAE15E581@linux.dev> <4A32F5E6-977D-4720-8723-B19AFBC08FCF@linux.dev> <7cb3dd91-f518-49b6-b311-9ec807b3c63b@linux.dev> <20261028080635.GD2668804@noisy.programming.kicks-ass.net> <20261028133439.GK2668804@noisy.programming.kicks-ass.net> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261028133439.GK2668804@noisy.programming.kicks-ass.net> X-Rspamd-Queue-Id: A5233C0014 X-Stat-Signature: uzb1nqoj6qn8mt9g8fn8wytpkmctbe16 X-Rspamd-Server: rspam04 X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793197029-92117 X-HE-Meta: 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 FUass5/h npmlhJjVMmNXCtp2U9LRC/uCg9kfTGHgd+U452dCUQaCLXRQx/K0agsm0aqtpTxmORbveYwD4kx3kk4uRulOP5wI3HvfL3t5YUGXmdiWf1Otx0GcPqQSH/jVSXi5cp6GStodYZlgd+keRBI45eazxFesCYFscPU2o3K8FFZbliz1JVcIWsyhjA5Q6lUj+gsw4SBTTMk7va6DFvtf7J4yk/w7baFvWK/36+68wbgkVneRQ2rgV8yOLFCadfR36XBcrHbGzw4p6eqCRarYxQZj5h/CwUer9OCEPC4+4qSkT542aXHLducQuDeBnQ8RxsUinP8WSbhHuNJAjhu0Xddn26OlAPoCF7IyMwTkh Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Oct 28, 2026 at 02:34:39PM +0100, Peter Zijlstra wrote: > > Only architectures with HVO matter here: x86-64, riscv and loongarch. > > arm64 has had it disabled since 060a2c92d1b6. > > Per that commit, could it be re-enabled now that its no longer marked RO? No. The problem there is the PFN change on a live vmemmap PTE, which needs break-before-make on arm64. Dropping RO only removes the permission change. James Houghton is working on it with an Access Flag trick: https://lore.kernel.org/r/20261003002123.505555-1-jthoughton@google.com arm64 will need the writable tail too: its atomic_fetch_add_unless() is a CAS loop. -- Kiryl Shutsemau / Kirill A. Shutemov