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b=DWrKodc5blYaVI69fJIrDSGH9j1sOrV8vB/q+sxVcMiuegDCijI2eRY2C+QCv/Pt/ V48UICyFiQu0MJt6Tgvw+XCneKVq7WnO98Ra1wmnoD3UprrvqDlEcMTMZW9nQ1A55A OOQgdH9I1bK5jXj+G87t3EJdSmIF6fCi6c/+tMJH221Hzq4HefplVg6JR4cG9I8x+h l3WGHKuEOxXQdQiQF1zKEL3LtqAUNhFwp+XOUcZXNAiIAKMwgprnJDP5ho5q4pc3Oz leMwxhzxP6mb2GKe8FflUvRnj5F44WzvRAw2cqCYJM02hvDuII3R/l96N/Hwiidb3t XoG+Ue2Tcs8eA== Message-ID: <16ae0a30-c6ee-40ad-98c8-ee6f4713e653@kernel.org> Date: Wed, 26 Nov 2025 11:28:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: use standard page table accessors To: Wei Yang Cc: akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org References: <20251126064723.4053-1-richard.weiyang@gmail.com> <9c32675d-c48d-405f-a38f-4c90a8edac74@kernel.org> <20251126100330.n66n3uvt3junflao@master> From: "Christophe Leroy (CS GROUP)" Content-Language: fr-FR In-Reply-To: <20251126100330.n66n3uvt3junflao@master> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: BCD92140011 X-Stat-Signature: 5gdypx1poksypbbsmqc4m9miyos7rugb X-Rspam-User: X-HE-Tag: 1764152924-561145 X-HE-Meta: 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 xB1cIB3O KesFfG6t1YVX/p56ju9FvrEBT/8PzXzqEuOs/KCzBUnmurpigphv3GiVkBvp9EdoMuozXu7b62kzXj+WzF7Zx3E5iTgGP0kBqQdzzQ39hCmGE/jbZm4yqXYo9/IaU5qlINP61Ko7NruqoLcYXMZFWXMeeGPGg8u6nkpbBgqpmIlBleEBQOPC0AHJVfDrHnY3ZpYdNwQZEkkv/yvb4WzCa/rrWLfIVxz7beYJAM36iRSRBJqKsJ0DrdjxVHEozzaJB20qT8a9vHfZ1lo9DEtTmNPxJE5k2NhQMOm/m50T5s6dJagysrnis9QmHido+p3q29tLnJeThhU9yXegyZ5D33giASEZBNpdjYPDinI8BCIEN0YvCN1Q6oiAZAsvEMmcyuAzi7hti4xCyk40qga8GZfPL9keMMGUWP9GcbFi0TU60dValYUBNQKQbhn8oU3APt8XJQ4ITYNfIgnvz0XzaZb542P6PD1zRquigb0V1Pukh0vI= 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: List-Subscribe: List-Unsubscribe: Le 26/11/2025 à 11:03, Wei Yang a écrit : > On Wed, Nov 26, 2025 at 09:15:24AM +0100, Christophe Leroy (CS GROUP) wrote: >> >> >> Le 26/11/2025 à 07:47, Wei Yang a écrit : >>> Use standard page table accessors i.e pxdp_get() to get the value of >>> pxdp. >> >> Please provide more detail of why you want to do that and how you are sure it >> doesn't break existing implementation. >> >> There was similar tentative in the past already which proved to give >> suboptimal results, see discussion here: >> >> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2Ff40ea8bf-0862-41a7-af19-70bfbd838568%40csgroup.eu%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C63a7608567de4df0a16308de2cd31076%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638997482180349327%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=ly4LRRjkKqQNBY6ZpkbHS7%2B0xuu2c1r0op1eysPtbSQ%3D&reserved=0 > > Interesting. > > The reason is P4D/PUD/PMD on PPC32 actually just has PGD/PMD. So it is not > necessary to retrieve P4D and PUD. More exactly, PPC32 just has PGD and PTE, no PMD either: arch/powerpc/include/asm/book3s/32/pgtable.h:#include arch/powerpc/include/asm/nohash/32/pgtable.h:#include > > If this is the case, sounds other platform with less pagetable level would be > affected too. Indeed. > > And this looks only affect when we walk the pagetable from pgd. If we just > iterating pmd/pte, we won't have this issue, right? Maybe. I have not looked at your changes in details, it just lit up a memory in my mind. Christophe