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[2003:d8:2f12:1b00:5d6b:db26:e2b7:12]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a6e8051018sm3950725f8f.16.2025.06.25.00.36.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 25 Jun 2025 00:36:54 -0700 (PDT) Message-ID: <8691d74b-67ee-4e26-81ac-f6bf1725361e@redhat.com> Date: Wed, 25 Jun 2025 09:36:53 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 0/2] fix MADV_COLLAPSE issue if THP settings are disabled To: Lorenzo Stoakes Cc: Hugh Dickins , Baolin Wang , akpm@linux-foundation.org, ziy@nvidia.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, zokeefe@google.com, shy828301@gmail.com, usamaarif642@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <75c02dbf-4189-958d-515e-fa80bb2187fc@google.com> <9cb94544-f65a-4394-b1e2-bfb226ead31c@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: JYIYtQ37J0eLb3jpgTVMk8v2nF1fEe_G75dAK1z-V7U_1750837016 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: DA906C0009 X-Stat-Signature: wmpyfn3z1ozapwr8w7ojycr9o4i6mfam X-Rspam-User: X-HE-Tag: 1750837021-82442 X-HE-Meta: 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 /zakETsa zNhc63lYYy1tRWieVE4vjPBo92cYz1MwvPNV8JtJBnB4hR0QVjzMe79i0RMy/G90LdE1oLzOzrDzbTpkw+XP31hmFlp1hTV17RcnSaibCB9nIBp/yOiWinbW9TAfllJKz8hceqNovMz2dmMzUtqwsouxJlHL3PRjOCgWrfpBIi+fviAH/KqyiM5SFPU3d9fWa1iF4SZFDReGJbLsvXTYVB3PKe1JDgV0rHRgHd35nzcLIMjUjEx3WYUW22ga7AKPpStXp/pLibhEWmcBuuS2Ucgh2CeMTYV5dF/KikepjMJGpLxoMS3TUadUPGOWVvr3X/HueXiCwH4kkSFxbaGO/JXi4vLDSYg78l+nwlMGtxYwNYNzgTtyVUarnrGCtoqs8XMhEl6rZpGpzAd/xE8xYo11fPDDSvElXqtF6vN+V104rMkN1fPWDw26KYEf93mlzzoPBxynpLfzrzr8= 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 25.06.25 09:30, Lorenzo Stoakes wrote: > On Wed, Jun 25, 2025 at 09:23:31AM +0200, David Hildenbrand wrote: >> Well, one could argue we broke user space (admin settings) when we converted >> "never" to no longer mean "never", but "never by page faults + khugepaged". >> And we did so without updating the documentation. >> >> I finally went back and checked the original discussions and, yes, this was >> deliberate [1]. >> >> As so often, we created a mess with THP toggles. > > I mean... !!! > >> >> Probably best to fixup the "never" documentation, and state that there is no >> way to disable MADV_COLLAPSE anymore. > > I disagree on the basis that system administrators will absolutely expect: > > # echo never > /sys/kernel/mm/transparent-hugepage/enabled > > To disable THP. > > I _guarantee_ you that's what nearly everybody except a handful of people will > expect. I know, See my other mail, the problem is rather if there is no somebody relying on never+MADV_COLLAPSE from doing the MADV_COLLAPSE-documented thing. It's a mess. (I have the suspicion that Hugh might know of such a user :) ) > > If we do decide to not do this series, _please_ can we seriously update the > documentation to be _absolutely crystal clear_ about this. > > I will volunteer to do this in this case :) > >> >> I agree that if we want a way to disable all of them, we better have a >> "deny" now. ... until someone else breaks that, then we can have a >> "really_never_deny_all" etc. ;) > > I really really dislike this. 'Deny' is weaker than 'never'. And now we have to > add even more complexity to the thing. See my other mail, for shmem_enabled "deny" is stronger than "never", lol. -- Cheers, David / dhildenb