From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A885FF4198E for ; Wed, 15 Apr 2026 10:37:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=akiAmAyh8lCTBxYdaxPA4DzOnhkzNxxi3xIqsHTRUR0=; b=Vxhfpe3EyGFl5VB0RwmX1XiehM b43bR52tH4JlLqpFwqqTw93m1jcbtTzINYOCuGRfdc/NgumjBZyBDegn45jBhK+ZvMG9s6KiURjqz ysBjM5LjLkn1GfQUEZo48eIBVXaZmgo/eMTzkTUzkSMbPNYmngYTeQzWEXjOblj8Iqpf15DTD7QAV z5p7plwViSWvs8OWByeFybjWpAbsfg+jTRN28bjjTSHlYBENZsBS31KnzT9fbTf0OCa3zWoGG9g21 HqCaHtOr918oknIdDGTpcEBIZbsewwvk6n2rKCa0gFMH0pZIkVC2LmMSxb3xjDPAhxZVf+DujVXtX GlheZEGw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wCxcy-00000000yhb-3PT0; Wed, 15 Apr 2026 10:37:48 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1wCxcx-00000000yhV-3bp5 for linux-arm-kernel@lists.infradead.org; Wed, 15 Apr 2026 10:37:47 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id EFB06600AD; Wed, 15 Apr 2026 10:37:46 +0000 (UTC) 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 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 X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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