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[217.140.110.172]) by mx.google.com with ESMTP id qh16si729581ejb.181.2019.07.04.08.26.18 for ; Thu, 04 Jul 2019 08:26:18 -0700 (PDT) Received-SPF: pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) client-ip=217.140.110.172; Authentication-Results: mx.google.com; spf=pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8316F2B; Thu, 4 Jul 2019 08:26:17 -0700 (PDT) Received: from [10.162.40.119] (p8cg001049571a15.blr.arm.com [10.162.40.119]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3B3A43F703; Thu, 4 Jul 2019 08:26:13 -0700 (PDT) Subject: Re: [PATCH V2] mm/ioremap: Probe platform for p4d huge map support To: Andrew Morton Cc: linux-mm@kvack.org, Catalin Marinas , Will Deacon , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , "Kirill A . Shutemov" , Michal Hocko , Stephen Rothwell , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org References: <1561699231-20991-1-git-send-email-anshuman.khandual@arm.com> <20190702160630.25de5558e9fe2d7d845f3472@linux-foundation.org> From: Anshuman Khandual Message-ID: Date: Thu, 4 Jul 2019 20:56:40 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190702160630.25de5558e9fe2d7d845f3472@linux-foundation.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 07/03/2019 04:36 AM, Andrew Morton wrote: > On Fri, 28 Jun 2019 10:50:31 +0530 Anshuman Khandual wrote: > >> Finishing up what the commit c2febafc67734a ("mm: convert generic code to >> 5-level paging") started out while levelling up P4D huge mapping support >> at par with PUD and PMD. A new arch call back arch_ioremap_p4d_supported() >> is being added which just maintains status quo (P4D huge map not supported) >> on x86, arm64 and powerpc. > > Does this have any runtime effects? If so, what are they and why? If > not, what's the actual point? It just finishes up what the previous commit c2febafc67734a ("mm: convert generic code to 5-level paging") left off with respect p4d based huge page enablement for ioremap. When HAVE_ARCH_HUGE_VMAP is enabled its just a simple check from the arch about the support, hence runtime effects are minimal.