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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-41fccbe8fa6sm457113275e9.2.2024.05.21.02.18.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 May 2024 02:18:42 -0700 (PDT) Message-ID: Date: Tue, 21 May 2024 11:18:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/2] mm/memory: cleanly support zeropage in vm_insert_page*(), vm_map_pages*() and vmf_insert_mixed() To: Vincent Donnefort Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Dan Williams , rostedt@goodmis.org References: <20240430204044.52755-1-david@redhat.com> <20240430204044.52755-2-david@redhat.com> <3decc6c8-9035-44d6-89c6-8d42a5e0bc40@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-Stat-Signature: grgt5kx7kgy3cmai6b3w7kgswmh8p41g X-Rspamd-Queue-Id: D8AACA0009 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1716283126-130898 X-HE-Meta: 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 DooWpj+D 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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: On 21.05.24 11:06, Vincent Donnefort wrote: > On Tue, May 21, 2024 at 10:25:43AM +0200, David Hildenbrand wrote: >> On 17.05.24 17:07, Vincent Donnefort wrote: >>> Hi David, >>> >>> [...] >>> >>>> -static int validate_page_before_insert(struct page *page) >>>> +static bool vm_mixed_zeropage_allowed(struct vm_area_struct *vma) >>>> +{ >>>> + VM_WARN_ON_ONCE(vma->vm_flags & VM_PFNMAP); >>>> + /* >>>> + * Whoever wants to forbid the zeropage after some zeropages >>>> + * might already have been mapped has to scan the page tables and >>>> + * bail out on any zeropages. Zeropages in COW mappings can >>>> + * be unshared using FAULT_FLAG_UNSHARE faults. >>>> + */ >>>> + if (mm_forbids_zeropage(vma->vm_mm)) >>>> + return false; >>>> + /* zeropages in COW mappings are common and unproblematic. */ >>>> + if (is_cow_mapping(vma->vm_flags)) >>>> + return true; >>>> + /* Mappings that do not allow for writable PTEs are unproblematic. */ >>>> + if (!(vma->vm_flags & (VM_WRITE | VM_MAYWRITE))) >>>> + return false; >>> >>> Shouldn't we return true here? >> >> Indeed, thanks! I wish we would have user in the tree already that could >> exercise that code path. > > I have a patch ready to use this path from the memory map tracing! I can either > send it once this one is picked-up or you can add it to your series? Whatever works for you! To debug, it would be good if you could send me the patch and simple instructions on how to test it (do we have a selftest as well?). > >> >> [...] >> >>>> @@ -2043,7 +2085,7 @@ static int insert_page_in_batch_locked(struct vm_area_struct *vma, pte_t *pte, >>>> if (!page_count(page)) >>>> return -EINVAL; >>> >>> This test here prevents inserting the zero-page. >> >> You mean the existing page_count() check? or the (wrong) vma->vm_flags check >> in vm_mixed_zeropage_allowed() ? > > I meant this page_count() here. As a quick test, I removed that check (also fixed > the vm_flags above) and the zero-page was properly mapped! That's weird and might indicate another issue. The refcount of the shared zeropage should be initialized to 1, just like for any other reserved pages (mm/mm_init.c:__init_single_page()->init_page_count()) Hm ... -- Cheers, David / dhildenb