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[2003:d8:2f26:ba00:803:6ec5:9918:6fd]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b50dd02ebsm10113115e9.9.2025.08.21.13.43.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 21 Aug 2025 13:43:37 -0700 (PDT) Message-ID: <95012dfc-d82d-4ae2-b4cd-1e8dcf15e44b@redhat.com> Date: Thu, 21 Aug 2025 22:43:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 00/13] khugepaged: mTHP support To: Lorenzo Stoakes , Nico Pache Cc: Dev Jain , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, ryan.roberts@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, kirill.shutemov@linux.intel.com, 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 References: <20250819134205.622806-1-npache@redhat.com> <38b37195-28c8-4471-bd06-951083118efd@arm.com> <0d9c6088-536b-4d7a-8f75-9be5f0faa86f@lucifer.local> <5bea5efa-2efc-4c01-8aa1-a8711482153c@lucifer.local> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: AE70F40003 X-Stat-Signature: f59gxjtnhebxz86k6p787bbrsz9wi9j5 X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1755809026-393335 X-HE-Meta: U2FsdGVkX19khJ2V6yxhlCFm7r/see9ctcVjLR8PxpiU2Gd9wIT6coFrMLVACjPt6RrOa1m/kkKRAkpZEKh1ucQC+3d11SJK5SyApabTTzgfOC/BSr9O2owg3N7qVaPMkOgpBscCjsZJluI1UDdV4gxX9rzOxGU6q5L0uh2e/o9dauMEnMhXxn9D5cHxYLMh/JD/4aaRsbBZIAYd4sTgKJ6u1i2+7gHbm1nONswCWwiOyggmMvk0MKhsxhK5q9Dp9oRUtWYGrSpF5KIs3iNqbet5iY+CZynLvAAi2+Jq2qmvDWQsRe09wuCtjZY6D1KWg1E2lsXkobbJPsl6FkIBhlhIi71OJkAeSld+Uygh2BH8T2HLLtms8tktlqaz5QWSIyar+ZzBsByDalCdMkXuChzcYwvCLGNIDEejOPY2Wr7LRannCuJa6xxSH+RJS7pUqtSqEAjyHjK/hLVUN2852MjR902OwPXBQtJi7Jh0/OMaoYXMuChoIugpDbxsadLYMjqwky1YwxZ8GkCJaYmvMB5/ktJCoAT/L9Ag+XOYbjB5Wft4TolffzPsK/czYnGtaO7lsS/wbyU16tVpAWweE50ifYm+mxOw09jrvghv2vizRxE5wP8KzJ7VTD3FNhUmdgQ6RSDb3GLZ6kRl8dvBkcAq6gvPVK/tp95DNDipEPy+imJR6s78/nJ2Y2PpbH1sG1DfHT6mUiwwQJkEDjx1cwwSiLa2wrDuttpELqS9AwO4KkKEFiWy+xa6ppGWvbV5wcRWVHkhr0NjO/FPKk31HNa1zTbQJm0A7G9sJ8C3svoogn2R67vCY01YKLak4QyHBglQD5OxBcepifToUd8xwLZShQ4mPaMhHDBVa/+Nz6Q+Z0B14l0LdfH9AK7g//ByTAttrzTlbjJitRl3a5jrKYggILPT5gZFfr3lwu0dXDb0OenzUMh0Wm49+Awn+aHpM82KbEh1wdVvHCn72hb Ou6oPoGn 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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: > > The one thing we absolutely cannot have is a default that causes this > 'creeping' behaviour. This feels like shipping something that is broken and > alluding to it in the documentation. > > I spoke to David off-list and he gave some insight into this and perhaps > some reasonable means of avoiding an additional tunable. > > I don't want to rehash what he said as I think it's more productive for him > to reply when he has time but broadly I think how we handle this needs > careful consideration. > > To me it's clear that some sense of ratio is just immediately very very > confusing, but then again this interface is already confusing, as with much > of THP. > > Anyway I'll let David respond here so we don't loop around before he has a > chance to add his input. > > Cheers, Lorenzo > [Resending because Thunderbird decided to use the wrong smtp server] I've been summoned. As raised in the past, I would initially only support specific values here like 0 : Never collapse with any pte_none/zeropage 511 (HPAGE_PMD_NR - 1) / default : Always collapse, ignoring pte_none/zeropage Once could also easily support the value 255 (HPAGE_PMD_NR / 2- 1), but not sure if we have to add that for now. Because, as raised in the past, I'm afraid nobody on this earth has a clue how to set this parameter to values different to 0 (don't waste memory with khugepaged) and 511 (page fault behavior). If any other value is set, essentially pr_warn("Unsupported 'max_ptes_none' value for mTHP collapse"); for now and just disable it. -- Cheers David / dhildenb