From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id B6535606AA2C for ; Tue, 27 Oct 2026 12:31:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=X+e0Bvce Received: by kanga.kvack.org (Postfix) id C45536B0700; Tue, 27 Oct 2026 08:31:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C1C286B0701; Tue, 27 Oct 2026 08:31:23 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B32CD6B0702; Tue, 27 Oct 2026 08:31:23 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 915126B0700 for ; Tue, 27 Oct 2026 08:31:23 -0400 (EDT) Received: from smtpin23.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 3594FA7ED4 for ; Tue, 27 Oct 2026 12:31:23 +0000 (UTC) X-FDA: 85368341646.23.D315819 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf23.hostedemail.com (Postfix) with ESMTP id 29AD914000B for ; Tue, 27 Oct 2026 12:31:21 +0000 (UTC) Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=X+e0Bvce; spf=pass (imf23.hostedemail.com: domain of kas@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=kas@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793104281; b=31QSm3BWgt7yCxQ5bA4a0de7snIEWbKsIuJ83XqHFI+vofKhNIYiYc4duYWymiqItI0kI8 +7q3DkutJv/wxBrTaEuqRq9dpbsry65Ae6+aFHOBrtAzUVPyYTB5nvkYgtXChPjua+6Wy+ I5GIRJqJrUQfb3EByUwxiyQ7B6Ncza4= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=X+e0Bvce; spf=pass (imf23.hostedemail.com: domain of kas@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=kas@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793104281; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=JA8h9KUew4bMbADI2oUInBzixioja4qGJWsGZbSCJpI=; b=ooLt6vKQwLmbBMzwBsm19FENOxIhHBZLrVbk3E4D4UeoLXxn0sucCioiKS1jNB8nqia1Cf pIdcBc+2LF6+GQDS4mHCYIBseaRzTpJCznbZGxDemD8FUEeLKWymZn/VZyl/q2lfjNGrJw f1scs5+rRFZTn1sBiXbDT8QLv3iDaDI= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 4A05C43BCF; Tue, 27 Oct 2026 12:31:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 05C791F031E8; Tue, 27 Oct 2026 12:31:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793104280; bh=JA8h9KUew4bMbADI2oUInBzixioja4qGJWsGZbSCJpI=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=X+e0BvcexZwh/4AUnHQPe+d1YBwAqRcptdi8/Y360+KTdQMvrRBMo8bCd3Rg7pkjr jfR9skKJCbBQUMZqJGiBNCLBi5gH6BVcLZ0GgQ3+2X/G3t9EryZbMxC+LsCqAiP1qw DfEfACQz/D/ZpUqjz9dgH0VUCxkYU771b7/ph67qzFsU4AEno08ZvoXbxxTgWcmYvl 6zo7JiiNXHjlpfjJMU7RfZombHjSCq75bqaQ7fC8OhmztiCuY+9yfCmCk61JR6zHhB OUKFXOmOR9BBW7Mp3w0zw9jNgjYqIEIRzdi5aBqJboCWtprx9MDOF1UIK0XZDyB36R YX+eBtDE94n1g== Received: from phl-compute-05.internal (phl-compute-05.internal [10.202.2.45]) by mailfauth.ams.internal (Postfix) with ESMTP id C4148198003A; Tue, 27 Oct 2026 08:31:11 -0400 (EDT) Received: from phl-frontend-04 ([10.202.2.163]) by phl-compute-05.internal (MEProxy); Tue, 27 Oct 2026 08:31:16 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: dmFkZTFr3RumHCfbQTlQHvPlXFybAsM2kuRamaLK+DcsHGJnUk2aCjGXXyr6NKWi0kroSr Oe85i3AcnkoxYUwKMUsCnYv3ol8I9M8cSn01GHV9AOTm5NfBjd+kCIjHiud1PAPzD5uXXl fN+b6rTVdtgXXvR1Z8eNRwhKI9yHxfQGGUEg7jRZegVt2fzj4kjjkHnB7T87ApQJ/YAHeu jWBHnlmzJHluxF9tAeEQxnoK263SXj0iYueuHFhGeOpOuCn6b2DvTIZwBEgN/+EwunXjB8 CwEWM/ocJ/P7R/h2BXkq5SQ2kHartw+7bNjA0Gxa9vs0WmUsZFcGkZnIAoPCICn1WzThUZ qOz0AVGhp67x0YgaM1Ydxlnbw0N39OED89qvX5lcwiSM/HqWSxoVFWvTjUWcewSd7SviP7 dQ04WcBrJE49hc8irsEuh6Xa8qmKhTv5+27sFoWEYs8ENR5FLW6D7hiRnsGUpkMI5MQceB UY8D9iJZ2kbY+0kfGnpFDbFzlSAgxEsNQH68IGiYsMcu566/hZL7hfXo0u3QYxpuXTE7Lf O/lVEviaducfFiifqy28iVecFxFVMJPrtttgxyJ2XsNCKh4pSCNIqqAiDWXSVimljJQasr nahIdUaatb5eDNRDlsczlK7MH5d2+R1Yg4ux3pWMJw8eTuDTZQQKwN8030Jg X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Tue, 27 Oct 2026 08:31:10 -0400 (EDT) Date: Tue, 27 Oct 2026 12:31:09 +0000 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: Peter Zijlstra , Andrew Morton , Muchun Song , 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: <20260227194302.274384-1-kas@kernel.org> <20260227194302.274384-14-kas@kernel.org> <20261027110028.GH2668564@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: X-Rspam-User: X-Rspamd-Queue-Id: 29AD914000B X-Stat-Signature: d9h7nkhtkmnbtedtbe9cqz8464pq4z4b X-Rspamd-Server: rspam01 X-Spam-Status: No, score=-6.1 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-HE-Tag: 1793104280-832174 X-HE-Meta: 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 DHiKuMS0 SbkGllzyPhNRS5cef0tcmnQuod3+GaWZgVCwLK8RIudhpG2aJfbJlNAb56LPaD6OxPvvdIo0HqhGvx9mMQfiqkTNadMkbBwT4D3K5dTM1jqScKGc5fQ5jqJLUsl9GgxutDq0CIN27p8LJBpT2nGbMmF1RujJSGXcwo95mjnLB4oRwmePQYEualcraRT4CN4SaKUssXSNjxdjU4TSK/5VRk/31L045pxaxZHlWWZEebMwV2j4uMSkVJdaju+aeLss5HpfsVcrMYs+ue/wP3V/rPI50UA== 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 Tue, Oct 27, 2026 at 01:05:58PM +0100, David Hildenbrand (Arm) wrote: > > Writing this, I just realized that we have another option -- map the > > shared tail page writable. A failing LOCK CMPXCHG writes back the value > > it read, and the get never changes a zero refcount, so the race becomes > > harmless. The cost is the protection: the page is shared by every > > hugetlb folio of that order in the zone, so a stray write to any tail > > silently corrupts all of them instead of oopsing. > > Right. Without HVO we would just corrupt pages in the single folio (which is > also not nice). > > I'm also questioning whether we need this RO protection all the time active. What do you have in mind? RO only under a debug option, or switching the tail page to RO some time after the remap? If it is the delay, a grace period alone does not close the race. We would need rcu_read_lock() back around the get, and then it is the old scheme with the wait taken off the allocation path. -- Kiryl Shutsemau / Kirill A. Shutemov