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Wed, 26 Nov 2025 04:15:33 -0800 (PST) Date: Wed, 26 Nov 2025 12:15:32 +0000 From: Wei Yang To: "Christophe Leroy (CS GROUP)" Cc: Wei Yang , 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 Subject: Re: [PATCH] mm: use standard page table accessors Message-ID: <20251126121532.tfwnlyaemak6qtb2@master> Reply-To: Wei Yang References: <20251126064723.4053-1-richard.weiyang@gmail.com> <9c32675d-c48d-405f-a38f-4c90a8edac74@kernel.org> <20251126100330.n66n3uvt3junflao@master> <16ae0a30-c6ee-40ad-98c8-ee6f4713e653@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <16ae0a30-c6ee-40ad-98c8-ee6f4713e653@kernel.org> User-Agent: NeoMutt/20170113 (1.7.2) X-Rspamd-Server: rspam12 X-Rspam-User: X-Rspamd-Queue-Id: 946A6C0019 X-Stat-Signature: zdaotnqdaixeyq3d4j6uw4sjbqb6p5wh X-HE-Tag: 1764159335-874763 X-HE-Meta: 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 nIFBXOot 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 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: On Wed, Nov 26, 2025 at 11:28:37AM +0100, Christophe Leroy (CS GROUP) wrote: > > >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. > Thanks for noticing me this, I learned a lesson from you :-) >Christophe -- Wei Yang Help you, Help me