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Wed, 10 Jul 2024 21:53:05 -0700 (PDT) Received: from [172.20.2.228] ([4.28.11.157]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fbb6a2c0dasm41719515ad.108.2024.07.10.21.53.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Jul 2024 21:53:05 -0700 (PDT) Message-ID: Date: Thu, 11 Jul 2024 06:53:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 00/45] hugetlb pagewalk unification To: Oscar Salvador Cc: Peter Xu , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Muchun Song , SeongJae Park , Miaohe Lin , Michal Hocko , Matthew Wilcox , Christophe Leroy , Jason Gunthorpe , Ryan Roberts References: <20240704043132.28501-1-osalvador@suse.de> <617169bc-e18c-40fa-be3a-99c118a6d7fe@redhat.com> <84d4e799-90da-487e-adba-6174096283b5@redhat.com> <9d5980e3-72e6-4848-b1ac-83ffab8522c4@redhat.com> <0f01c613-9e4f-47b6-af2b-09aa90437d90@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-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: A2B6B4000D X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: msep9qmyzfxcf6r8b143t9mecb9i1qi1 X-HE-Tag: 1720673590-258087 X-HE-Meta: U2FsdGVkX1+S7XcLhsDAVxbgW+QP4ih0Yld9wc/9tM/miWo0QieA6u4MlIwd/AQ+3CZsOw5A6emriw/hq8BNQIahJS4mJ0/G5wVcaEZ6rRggvxt1sTzD2L51CKSCHv2NqPKqlOS0yJSA0hdrdqgTkQgmp2EP7bkUPU5rSuINV5J0m7Fbv//OhW4L3tiy2V3g9x6f3Ba+B05YKA0qCGPBr4Hz/xNN0HQQvAqGz9L9l+VH45o611uFqfZixd1C/TGs9mgcvVqcVH4jLadPOVWkQ5LfTh6Rig+SNvyIngqF5sW1EzYJlHWY1urKo0dFZYYlgShaDC3g8H3yyzUOwB6ApPKomRv8gcCMoE2RVnNB6JheNT5tsyzUDl78+JbxazT9qyaHFs/IsfPTdocZ3fwf1DMclDdhEqmm0nN08iK93n/sVWjPXBz3xlfIKJiaZBlUDLPvjJt6qpHDIF77GB4Fyhfs3qFJZHj6IffoXm/W4Q1XhDWnY/ICus8E+Y2AO8GzsplbtNH9zyj/59qRBHEESct2rWg6cWWuXUbC1FaYb9vXp8/KBy82Ag2UMIvYPGrS4tOd+GRBT3nt78UeiXorbeeGl1HMBw9MQjVz9ZncasKMXF7WpvaqwXhNIz5qlt4k8kbww20EU6aTLBHNSWhhFVy3XZkeENIwvGciwWAR3Y9wZEy7vChxdN/sXMP6IeRhNd489AO9FuVc9q9nTqICIgKnCNUQrmRMwOxUYzUbtmm6Be48r/tCSs5vQnErdizpMY6PIi/RJikKzZBDtyQOeaZCY8w0KkjnS6vc2I+GEO2cxXhrtk+co/leBo7wQvJZa72JAA/p2mAVOId+vT9LDFsjTiWqyvisFTIAQzKpOsk3gepxWlKHjp/ky3o0tZO9p4LP2ZDk65hQ+oYwzh3S/p1zTxmAYTNAd/Ecm8F5hMV4pQZ///PDGsz5LUaIYOBQNirmZhadE/NqFsdtymW sGrhigQr KaO1iw1IN0iqwJRIn9r1ybaFGOoidmIhKoNCIHRXxwlHluCYFLUnOzZQ3LuTkqso242xb7lP1urlMXWiysVHLQEqsa8mQvNC9cdSAzHz5bJBUZSw394lSEmO7tkkwvQHS+7C4uqLl5NFjivLS3ovpki2Fo7oB20L4dFPWqz0cTZpcl9JpadaWmBRjJPqEN6b9DPsRSjpPOjZNUEgM7nwg8KPGC4wPqjG8gdjBWoq7e68m63yRujTXl8GDHJXLxK+o60TFhlQJu5JoWPNE808qBxVtaItgIrJ11hO8yzF0PiBSK4DUjE+5WKsZVTsSZFj/MayHn+6pwnaC3sLvIf1rb6mADPgjeov4TjgN 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 11.07.24 06:48, Oscar Salvador wrote: > On Thu, Jul 11, 2024 at 02:15:38AM +0200, David Hildenbrand wrote: >>>> (as a side note, cont-pte/cont-pmd should primarily be a hint from arch code >>>> on how many entries we can batch, like we do in folio_pte_batch(); point is >>>> that we want to batch also on architectures where we don't have such bits, >>>> and prepare for architectures that implement various sizes of batching; >>>> IMHO, having cont-pte/cont-pmd checks in common code is likely the wrong >>>> approach. Again, folio_pte_batch() is where we tackled the problem >>>> differently from the THP perspective) >>> >>> I must say I did not check folio_pte_batch() and I am totally ignorant >>> of what/how it does things. >>> I will have a look. >>> >>>> I have an idea for a better page table walker API that would try batching >>>> most entries (under one PTL), and walkers can just register for the types >>>> they want. Hoping I will find some time to at least scetch the user >>>> interface soon. >>>> >>>> That doesn't mean that this should block your work, but the >>>> cont-pte/cont/pmd hugetlb stuff is really nasty to handle here, and I don't >>>> particularly like where this is going. >>> >>> Ok, let me take a step back then. >>> Previous versions of that RFC did not handle cont-{pte-pmd} wide in the >>> open, so let me go back to the drawing board and come up with something >>> that does not fiddle with cont- stuff in that way. >>> >>> I might post here a small diff just to see if we are on the same page. >>> >>> As usual, thanks a lot for your comments David! >> >> Feel free to reach out to discuss ways forward. I think we should >> >> (a) move to the automatic cont-pte setting as done for THPs via >> set_ptes(). >> (b) Batching PTE updates at all relevant places, so we get no change in >> behavior: cont-pte bit will remain set. >> (c) Likely remove the use of cont-pte bits in hugetlb code for anything >> that is not a present folio (i.e., where automatic cont-pte bit >> setting would never set it). Migration entries might require >> thought (we can easily batch to achieve the same thing, but the >> behavior of hugetlb likely differs to the generic way of handling >> migration entries on multiple ptes: reference the folio vs. >> the respective subpages of the folio). > > Uhm, I see, but I am bit confused. > Although related, this seems orthogonal to this series and more like for > a next-thing to do, right? Well, yes and no. The thing is, that the cont-pte/cont-pmd stuff is not as easy to handle like the PMD/PUD stuff, and sorting that out sounds like some "pain". That's the ugly part of hugetlb, where it's simply ... quite different :( > > It is true that this series tries to handle cont-{pmd,pte} in the > pagewalk api for hugetlb vmas, but in order to raise less eye brows I > can come up with a way not to do that for now, so we do not fiddle with > cont-stuff in this series. > > > Or am I misunderstanding you? I can answer once I know more details about the approach you have in mind :) -- Cheers, David / dhildenb