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[2003:d8:2f2b:fe00:532f:f82e:7128:936b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-442cd35fb09sm13252985e9.30.2025.05.07.14.24.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 07 May 2025 14:24:02 -0700 (PDT) Message-ID: Date: Wed, 7 May 2025 23:24:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] mm: convert do_set_pmd() to take a folio To: Matthew Wilcox , Baolin Wang Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, ziy@nvidia.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <8e33c8a65b46170dfd8ba6715d2115856a55b8f6.1746609191.git.baolin.wang@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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: v39i6jX665v0u0cr3BkmuKhXsGk9ZCbEKKST9WMGuOU_1746653043 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: rspam12 X-Rspamd-Queue-Id: 9A91D20009 X-Rspam-User: X-Stat-Signature: eshdfgm9zou9zjhnfsm5ajz55dipdw8t X-HE-Tag: 1746653046-125201 X-HE-Meta: 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 Pow36GGo u1CM9XI14ohHq4c9YwwGswoBntN2/VfZ1GXqbGKgvLzjWX7We4XWUqX8wd3lYEoFqrYqaXl+LSTM29jZFOsEyv5mk8PYpFwdZSpM97U/YJUi6VjtKENnatU36L/Z2H7oEr1KsCNyem8X+hmtK1SJJgzLs2PTDQYgui5MjZcMgfmxmYSGc8CnjpMipM8/VuSNh4eOgDHqqqNYL6nI99aLtK6jdYwzsc6L6zxiFXpxIEJiAn+Vnx1tqIs8aQK/yiAXLwtAQXXc1eHhNRcSI444LgciaaeXl2reR+6ywjGWjEsg0dI99zfmLJmKOgozlJirOyxwyf5tPZSxYumW7Unx1OUkC/kgbtFflU/UgJufKvlnJVHFLi/CLMmHQM+DQpOStPG9JbpNUKymd5M9Kthc9K4zaXsUYHLYeBXA/l1HGLpnlfXqSQELAZvNSvwvziwTDgq8LMSUDtMR9IVs= 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 07.05.25 14:10, Matthew Wilcox wrote: > On Wed, May 07, 2025 at 05:26:13PM +0800, Baolin Wang wrote: >> In do_set_pmd(), we always use the folio->page to build PMD mappings for >> the entire folio. Since all callers of do_set_pmd() already hold a stable >> folio, converting do_set_pmd() to take a folio is safe and more straightforward. > > What testing did you do of this? > >> -vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page) >> +vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio) >> { >> - struct folio *folio = page_folio(page); >> struct vm_area_struct *vma = vmf->vma; >> bool write = vmf->flags & FAULT_FLAG_WRITE; >> unsigned long haddr = vmf->address & HPAGE_PMD_MASK; >> pmd_t entry; >> vm_fault_t ret = VM_FAULT_FALLBACK; >> + struct page *page; > > Because I see nowhere in this patch that you initialise 'page'. > > And that's really the important part. You seem to be assuming that a > folio will never be larger than PMD size, and I'm not comfortable with > that assumption. It's a limitation I put in place a few years ago so we > didn't have to find and fix all those assumptions immediately, but I > imagine that some day we'll want to have larger folios. > > So unless you can derive _which_ page in the folio we want to map from > the vmf, NACK this patch. Agreed. Probably folio + idx is our best bet. Which raises an interesting question: I assume in the future, when we have a 4 MiB folio on x86-64 that is *misaligned* in VA space regarding PMDs (e.g., aligned to 1 MiB but not 2 MiB), we could still allow to use a PMD for the middle part. So idx must not necessarily be aligned to PMDs in the future. For now, we could sanity-check that idx is always 0. But the rmap sanity checks in folio_add_file_rmap_pmd() will already catch that for us. -- Cheers, David / dhildenb