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t=1780308567; bh=telDdSC7/EI4bm0my2SYNWvjV6/+1WMfaGUydwsM0JE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=E/RSr7+q/6nIFb+9C6c9jmKbP1es072hXYz1IQTGwUjqaPxnQ3p0yc/KbCu5ZwWW7 O4de5CsFCu+YBhZn0/qvFCVmXnhQZ+9bcoLMBeKqREXxlFIr5oU6mXmOrcX6VruVjp j5WG8L1x8M48jYN/AQiG6LpMUDMP96kfuQ5pbitNPPhKrhMEkpVqoLAjig4X1ATvh5 l1DeuNTi+4uytvO3r+WRDidfs8pVNImknpTmQZ48FHAhfLQgEP5r/X2x3TH3Ibx3rF WW0u5PA4rvSr7OS8rrXPbpZCp0JRJt7WiTn0MRU8VhZ3ldi28u+HEvu6N0aoZFitOS ihVHv9tWG1ZZw== Message-ID: Date: Mon, 1 Jun 2026 12:09:13 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v18 06/14] mm/khugepaged: generalize collapse_huge_page for mTHP collapse To: Lance Yang Cc: npache@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, liam@infradead.org, ljs@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com, usama.arif@linux.dev References: <2024af56-5e99-4799-a586-e9ba756cecb9@kernel.org> <20260601032804.96122-1-lance.yang@linux.dev> <1c99294c-9ebe-4856-bfde-09801701d75c@kernel.org> <32751424-8ad3-4fd2-9f07-8a4f5a98d632@linux.dev> 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-Queue-Id: D07631C0003 X-Rspamd-Server: rspam03 X-Stat-Signature: 4h7mo986hzumbou4b5mi7wd1tfj9cb76 X-HE-Tag: 1780308568-314488 X-HE-Meta: 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 LLJp0LFN MyZmcT4KMM6FAD/g6EAQCVhNtjPXNxGE4ql86ZZ6Sd9Wa4ZWKWcSflZ9aWlV12YLheM54baDl2jQyAAqV/tIDbAVhziFleA7J/hdqGLuzDJ9zsqYqkrfCOwWDrEyBMvByLr/RBVtox7KJrek+Rh3teB3AuS8YNc4yVZwIAUy5bQcE3rrkKFkdSMyPJCAfQvn+o37aubxsl797IpCsMyvj5dIkAg4cnzZTS0Xs6gsEQbEUhmnQWRb/xMVdw6AGPLQ6MtxQRmaQva3a0tZDN7Xl80i4yUO9x0wcuYU3QGF+RIAZmJpTl+oh6KaI434qtJ9kf0iysRt7z/VLQudljlg52oSmK3eSUYR45zoV+diJGG4aXSyf9pgdI1yAkQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/1/26 10:44, Lance Yang wrote: > > > On 2026/6/1 16:15, David Hildenbrand (Arm) wrote: >> On 6/1/26 09:49, Lance Yang wrote: >>> >>> >>> >>> I had Codex do the boring grep-work through the arch update_mmu_cache* >>> code :D >>> >>> MIPS doesn't seem to be the only code doing a re-walk, but it is the >>> only one I found that appears to assume the PMD/PTE walk cannot fail, >>> without checking whether the PMD is none ... >> >> Okay, but likely the other code that tries to handle it is also problematic. >> >> Best to make sure the page table is already installed when updating the entries. > > Neat, makes sense to me :D > > That way the page talbe is back in place before any arch hook gets to look at it :) Right. I don't think we could run into a deadlock here (nobody should concurrently take a look at the page tables in the first place). Not sure about the memory barrier I dropped: the page tables are already properly set up (just some entries cleared), so I'd assume that barrier might not be required. -- Cheers, David