From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0248D32A3C8 for ; Wed, 15 Apr 2026 10:37:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776249467; cv=none; b=nTmJbvSHA6H3ddVgoRKVHdT2Qtu9JHGD4asDrCVVHCCbBpvDEBtboR7l4Zai5H0X1dJPLAUQErahNMbJKHva1G17NQd+gnXZQrBvQnpr/p5GkO4FOTLqNs0rvEAeLcJric593AKMwd+jOoyO2fYraCCBsB9O9k5xiljHekJAhio= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776249467; c=relaxed/simple; bh=f66BS374o9yicV24P6l2YJ4oEbiJ5q8d6MqcbAuKZpY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=s1Tb1rNBtkTgERyfVt9jjRsfB0yL76DntrplBH29Vss39cbQzObYfqlAA11602/fbwre98Hq9+p5jqAXhJiLOHq1ONWaRoPvU4PANjK5kSlaDo5nahAhudADH12UdKy8ThnOaDmhGBsSwqIBLLHFjBFSE0+xb5ypL6KOTliub5Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rx3On75X; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rx3On75X" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CA067C19424; Wed, 15 Apr 2026 10:37:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776249466; bh=f66BS374o9yicV24P6l2YJ4oEbiJ5q8d6MqcbAuKZpY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=rx3On75Xszu4n08udrTE7xE5Lub7Qhmn8d6aHoDLCpcMivecgYsi+R9kxA4WDUkot 3kRT2phk8L1JqgxFxeHX3W5Cg+9OfdT/pIGVirrHJEio/bZaNHPkJ7LC5tHeN/Thaf hdf3oWWiDwiCyRomMDBKvCgkMRrIQ63Po32PbeUpQUIiMJd9GgjXGcm/PgMwMi9F/e qq+QzVzCZm2pdqAcxrPBMX91/7dNmw42kWK0boJM+SY63JKs/okeicjOH5o5OTho3X W7hrFbChtoIMW8dwsXSHLB4AWAkcZmWkg5Jw8RxxwEZiM1isQNv8jF5dQA06a0bJXw VCs9uLN82H4hQ== Message-ID: <4789eae4-2319-43ca-9141-72de767e071b@kernel.org> Date: Wed, 15 Apr 2026 12:37:39 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC V1 08/16] arm64/mm: Convert READ_ONCE() as pgdp_get() while accessing PGD To: Anshuman Khandual , linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas , Will Deacon , Ryan Roberts , Mark Rutland , Lorenzo Stoakes , Andrew Morton , Mike Rapoport , Linu Cherian , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com References: <20260224051153.3150613-1-anshuman.khandual@arm.com> <20260224051153.3150613-9-anshuman.khandual@arm.com> <37a7e502-ac1d-4573-a877-23b1bfd07238@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/10/26 07:30, Anshuman Khandual wrote: > On 08/04/26 5:49 PM, David Hildenbrand (Arm) wrote: >> On 2/24/26 06:11, Anshuman Khandual wrote: >>> Convert all READ_ONCE() based PGD accesses as pgdp_get() instead which will >>> support both D64 and D128 translation regime going forward. >> >> Please mention here why you move p4d_offset_phys/p4d_offset. (same >> applies to other patches) > > Will do that. > >> >> Do we get additional function calls that might degrade some page table >> walkers? > > Sorry did not get it. Are you asking if D128 adds new page table > function paths thus increasing memory access latency etc ? Each p4d_offset() etc. now does a function call. So during ordinary generic page table walking code (see folio_walk_start() as one example), you'd now perform a bunch more expensive function calls: pgdp = pgd_offset(vma->vm_mm, addr); ... p4dp = p4d_offset(pgdp, addr); ... pudp = pud_offset(p4dp, addr); ... That's not desirable. So I wonder if there is a way to just keep these things inline. Might have to move the definitions of pgdp_get() etc. -- Cheers, David