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Wed, 28 Oct 2026 09:04:39 -0400 (EDT) Date: Wed, 28 Oct 2026 13:04:38 +0000 From: Kiryl Shutsemau To: Muchun Song Cc: "David Hildenbrand (Arm)" , Peter Zijlstra , 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: <20261027110028.GH2668564@noisy.programming.kicks-ass.net> <070DDE5C-2183-4A8B-AC2D-891CAE15E581@linux.dev> <4A32F5E6-977D-4720-8723-B19AFBC08FCF@linux.dev> <7cb3dd91-f518-49b6-b311-9ec807b3c63b@linux.dev> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7cb3dd91-f518-49b6-b311-9ec807b3c63b@linux.dev> X-Rspamd-Queue-Id: B73D920015 X-Stat-Signature: wm7jy11o99nrrxf8o45ti4of9wtaw948 X-Rspamd-Server: rspam06 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: 1793192690-370203 X-HE-Meta: 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 fGQQNaN+ LQWD4cXmxFK5B0MLjytNwC8FZ724qZNojuMIeayGAYlcX+N+UJ9NXOfPZU9AGy+8zE8XZBj+cFmBWLONXNM32h820fJ+ylG5tP2Ox/n1MrGpTYBDNScnSDDYAN8SY0hVTy1XfX/y940GAywCCT9LCUzgcYFChxQDDq+VOzhFjLhvRiRi4VKI44eZtcsjzmyonZ2tGX6ut2u/2tTQx/ENH5+xy7tUarSZN0RvAsL0coBXLQ5KGpsnFu4j9ZDWuhwjinFf5jwIzfnT+lHm2Tn6UMJWWuA== 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 10:38:22AM +0800, Muchun Song wrote: > > Bootmem folios optimized in early boot get their tails mapped writable > > and write protected later. Drop the write protect step. > > For bootmem folios, I don't think the RO mapping should be removed, > because we are in the initialization stage of struct page. > No one should touch those pages at this point; otherwise, they could > encounter uninitialized struct page as well. This assumes no race > exists during early boot. > > Since such a problem does not exist during the boot stage, why should > we give up the protection that RO provides? Agreed. Nothing does a lockless get on bootmem folios before hugetlb takes them, so they can stay RO. I will keep the pre-HVO write-protect and post the patch. -- Kiryl Shutsemau / Kirill A. Shutemov