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[80.81.2.50]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-429952de4a1sm21724189f8f.37.2025.10.28.10.56.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Oct 2025 10:56:13 -0700 (PDT) Message-ID: Date: Tue, 28 Oct 2025 18:56:10 +0100 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v12 mm-new 06/15] khugepaged: introduce collapse_max_ptes_none helper function To: Lorenzo Stoakes , Baolin Wang Cc: Nico Pache , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, ziy@nvidia.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, akpm@linux-foundation.org, baohua@kernel.org, willy@infradead.org, peterx@redhat.com, wangkefeng.wang@huawei.com, usamaarif642@gmail.com, sunnanyong@huawei.com, vishal.moola@gmail.com, thomas.hellstrom@linux.intel.com, yang@os.amperecomputing.com, kas@kernel.org, aarcange@redhat.com, raquini@redhat.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, tiwai@suse.de, will@kernel.org, dave.hansen@linux.intel.com, jack@suse.cz, cl@gentwo.org, jglisse@google.com, surenb@google.com, zokeefe@google.com, hannes@cmpxchg.org, rientjes@google.com, mhocko@suse.com, rdunlap@infradead.org, hughd@google.com, richard.weiyang@gmail.com, lance.yang@linux.dev, vbabka@suse.cz, rppt@kernel.org, jannh@google.com, pfalcato@suse.de References: <20251022183717.70829-1-npache@redhat.com> <20251022183717.70829-7-npache@redhat.com> <5f8c69c1-d07b-4957-b671-b37fccf729f1@lucifer.local> <063f8369-96c7-4345-ab28-7265ed7214cb@linux.alibaba.com> <9a3f2d8d-abd1-488c-8550-21cd12efff3e@lucifer.local> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit [...] > >> towards David's earlier simplified approach: >> max_ptes_none == 511 -> collapse mTHP always >> max_ptes_none != 511 -> collapse mTHP only if all PTEs are non-none/zero > > Pretty sure David's suggestion was that max_ptes_none would literally get set to > 511 if you specified 511, or 0 if you specified anything else. We had multiple incarnations of this approach, but the first one really was: max_ptes_none == 511 -> collapse mTHP always max_ptes_none == 0 -> collapse mTHP only if all non-none/zero And for the intermediate values (1) pr_warn() when mTHPs are enabled, stating that mTHP collapse is not supported yet with other values (2) treat it like max_ptes_none == 0 or (maybe better?) just disable mTHP collapse I still like that approach because it let's us defer solving the creep problem later and doesn't add a silent capping. Using intermediate max_ptes_none values are really only reasonable with the deferred shrinker today. And that one does not support mTHP even with this series, so it's future work either way. -- Cheers David / dhildenb