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b=Y58b6cPMVo8J2OhRDndnK6601iFosf6b+BWTdqJuf5TJgY13o+V1z2ytjetxDbLvX cM8AS5OrOQi3t/QGgRVc/f0+K51FqRS/JpG/w1NpWGy15QzStMqQjuGtVNOA5eHpdH Ik/79viha99pjTJ2h+Fuk3sYEN9AgebCFUCGMkNer0Ui1eMD4wTKRsgl6JA4RHOe3w viW6yVFbBp5us5+6/Yt6lMrUkmBi0bOVfPiJXTKvUwKd9qYLdPziUuhCfhgKpfMGet VhMVV2+RAPJgLUyDBaUpXR6DeyuHyg++GYOtcy1nMuBBZOJ8Rj9jn9C7okb1+Q57c8 A05H/8TzZFXxA== Message-ID: Date: Fri, 9 Oct 2026 22:44:16 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/huge_memory: avoid transient none PMDs during lazyfree reclaim To: Zi Yan Cc: Kyle Zeng , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , stable@vger.kernel.org References: <20261009165214.40212-2-kylebot@openai.com> <8db35dc0-eb06-42e4-90f9-534522e810e1@kernel.org> <55765FF3-18D7-424C-984D-81C316F323E1@nvidia.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-Rspamd-Queue-Id: 8758780008 X-Rspam-User: X-Rspamd-Server: rspam12 X-Stat-Signature: 7rmdris9tt3xon4pjfhj6ddykby4hymq X-HE-Tag: 1791578664-729030 X-HE-Meta: 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 ClUKoDYh xmzALOp7JdfjROY38SMgZW2e9KJiuo5PV8ti1jPhPAnqEiv3EuyZE/P+IRQTeokuNPfZmw84w4sAMaYDq2LvzBPqqkQlmkdgxfWmZ83AmYkc3k3Y6QC2DSogbloHpsA5ijroPxsstyM1AqweJmolw7hBEhSNDE7nAu1Yez6wdT675VNMt6zsFaDSL5hBdmZlmOUaIo2izIXs74UIeP4nrSnH/tPLChHr3voa2Awbm+PSLFJpz8UsvS8U9JZm8XdugHlVv8EeQIBLJvBqh2TQ6Jy0FqckUZBC8gy+/p/L7XZ6XlRoIcHHb4d8MIA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/9/26 22:27, Zi Yan wrote: > On 9 Oct 2026, at 16:23, David Hildenbrand (Arm) wrote: > >> On 10/9/26 20:17, Zi Yan wrote: >>> >>> There are some gaps we need to close before getting this fix in: >>> >>> 1. GUP-fast cannot follow the invalidated PMD: riscv and LoongArch need >>> pmd_access_permitted() that requires _PAGE_PRESENT; s390's >>> pmdp_invalidate() needs a change. >> >> Ugh. We really need pmdp_invalidate() to have reasonable semantics. This whole >> PMD locking is a mess :( >> >>> >>> 2. sparc64's thp_pte_count can be imbalanced with this change (based on >>> Lance's offlist feedback). >> >> Ack. >> >>> >>> In addition, powerpc has a page table check issue similr to riscv, where riscv >>> fixed it with commit 9f4a88b8d01a6. This is not related to this issue >>> but discovered along with the investigation. >> >> Zi, do you have the capacity to take over this patch? > > Yes, I can take over it. My plan is to send a series including > patches for 1 and this patch as is. powerpc fix can be a separate one. > > Best Regards, > Yan, Zi If we need a quick stable fix we could temporarily disable the whole thing until it is fixed, just a thought. -- Cheers, David