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[2003:d8:2f09:f500:a38f:d086:59d4:9df]) by smtp.gmail.com with ESMTPSA id u11-20020a05600c138b00b003fefaf299b6sm7391785wmf.38.2023.11.13.01.26.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Nov 2023 01:26:49 -0800 (PST) Message-ID: <2f164fca-44bf-4594-a139-82870bc97be2@redhat.com> Date: Mon, 13 Nov 2023 10:26:48 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/khugepaged: map anonymous pte-mapped THPs by pmds To: Xu Yu , linux-mm@kvack.org Cc: akpm@linux-foundation.org, zokeefe@google.com, song@kernel.org, shy828301@gmail.com References: <5e56a480be9294108bff6ff0bcb0980dc7ee27d4.1699865107.git.xuyu@linux.alibaba.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: <5e56a480be9294108bff6ff0bcb0980dc7ee27d4.1699865107.git.xuyu@linux.alibaba.com> 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-Rspam-User: X-Stat-Signature: c6qcnxb39htohsocredqz4xspdshpf48 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: B698A18001C X-HE-Tag: 1699867613-10915 X-HE-Meta: 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 UASn0HSZ 1ESgD1/hiVjDT8Wm4YiT+4D+AzraOBi0zj4J1rF25zUvTLvJqAKhQkyuV+HbbqTo/75QlkNJHMhS/3tKvTjzjGWLMEROqi6XutbA9vc2vFyTgS45720o9qeuURkjCVYJkBSPa0mG3vBY0wLkCGeUtfVl+NtrO9eqAuhx6G33NGTTMyXVdpdtTsypoAHwHxZIWJu+pzxkUgfYzoQOSVp073u6FSTsirA/T91ZG+uvMls4/gIhDESnyW8iZT5xIoaY/Us8BorgtfCejBWONhfoJH4ix/edlihOy1OyC6RecOGOMif2tlibtpoZFw+22/aVcDqS3srFrL9bQkwCLsjHwEb6CObm/DYxsIXAJy/TfN+k/Ok5VHASu50zkFxLr77bB/yD/OcHWR1UT9tpKJnwV7ovdknrWXzAxx8wm2Lu70igWiT9ogGSV4r16NGe5WgCdT+Ob 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 13.11.23 10:05, Xu Yu wrote: > In the anonymous collapse path, khugepaged collapses pte-mapped > hugepages by allocating and copying to a new hugepage, which is > suboptimally. > > In fact, we only need to update the mapping page tables for anonymous > pte-mapped THPs, in the same way as file/shmem-backed pte-mapped THPs, > as shown in commit 58ac9a8993a1 ("mm/khugepaged: attempt to map > file/shmem-backed pte-mapped THPs by pmds"). Somewhere along that patch set discussion, there was a discussion about how to deal with PageAnonExclusive properly. Quite a lot of information is documented in: commit dee2ad120571f38433211098cd6b95a59bdfc8c7 Author: David Hildenbrand Date: Wed Jan 4 15:49:05 2023 +0100 selftests/vm: cow: add COW tests for collapsing of PTE-mapped anon THP Currently, anonymous PTE-mapped THPs cannot be collapsed in-place: collapsing (e.g., via MADV_COLLAPSE) implies allocating a fresh THP and mapping that new THP via a PMD: as it's a fresh anon THP, it will get the exclusive flag set on the head page and everybody is happy. ... I purely speculate that you didn't consider it and got it wrong, sorry :P Fortunately, I wrote a test case for that where it's documented (above) tools/testing/selftests/mm/cow.c tests: # [RUN] Basic COW after fork() when collapsing before fork() ok 169 No leak from parent into child # [RUN] Basic COW after fork() when collapsing after fork() (fully shared) ok 170 # SKIP MADV_COLLAPSE failed: Invalid argument # [RUN] Basic COW after fork() when collapsing after fork() (lower shared) ok 171 No leak from parent into child # [RUN] Basic COW after fork() when collapsing after fork() (upper shared) ok 172 No leak from parent into child If your implementation supports MADV_COLLAPSE, it might reveal any problems. -- Cheers, David / dhildenb