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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-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 9BC0940008 X-Stat-Signature: xk3jrncewqk1aq8sxdw9shr36ajtrhi1 X-HE-Tag: 1776249467-79963 X-HE-Meta: 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 j50BZc6C 2Q65XK5kcZeUwzksz7r213Q7epRdL8509LdhGS90BJ0yq+evh0EDDbKaHKbtA8DtLT51EwceRFO3ayJYrh8DyvXHaOX3K2hYQF4cCmC7FWl9b/aovUlipfOQ2/aQ3die/itS8zx2zmM+foBb/o1VkryqhnNfGTmAJpNGVAXRaMBL9TBJe07H3bC5w8b8EB4EpL/v+vt5L8ry3rYmL6Hfg0kHuYNop8nhtOzIejDkR+gZUGj7ypt1YReNOSfjnabiw6gVQh8IXLWKc1Iy1qE4v2pK8NxgwD1+o6HAbD7ZHwjs2tS7e6cRHpAX6rw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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