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[2003:d8:2f2c:5500:988:23f9:faa0:7232]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-454b168673asm23050705e9.26.2025.07.04.03.47.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Jul 2025 03:47:19 -0700 (PDT) Message-ID: <7a6903d0-0ba1-4536-aea0-08ff511f5149@redhat.com> Date: Fri, 4 Jul 2025 12:47:18 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 4/5] mm,hugetlb: drop obsolete comment about non-present pte and second faults To: Oscar Salvador , Andrew Morton Cc: Muchun Song , Peter Xu , Gavin Guo , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250630144212.156938-1-osalvador@suse.de> <20250630144212.156938-5-osalvador@suse.de> 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: <20250630144212.156938-5-osalvador@suse.de> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: d7ytONk3YCb-az74283IZL8JNf1NpoeEMLhY8uv5qrg_1751626040 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-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 314BDC000E X-Stat-Signature: embnr7c6bkyzw6nbboi7695gjtnfj4t9 X-HE-Tag: 1751626045-204381 X-HE-Meta: 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 rgqylbPZ 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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 30.06.25 16:42, Oscar Salvador wrote: > There is a comment in hugetlb_fault() that does not hold anymore. This > one: > > /* > * vmf.orig_pte could be a migration/hwpoison vmf.orig_pte at this > * point, so this check prevents the kernel from going below assuming > * that we have an active hugepage in pagecache. This goto expects > * the 2nd page fault, and is_hugetlb_entry_(migration|hwpoisoned) > * check will properly handle it. > */ > > This was written because back in the day we used to do: > > hugetlb_fault () { > ptep = huge_pte_offset(...) > if (ptep) { > entry = huge_ptep_get(ptep) > if (unlikely(is_hugetlb_entry_migration(entry)) > ... > else if (unlikely(is_hugetlb_entry_hwpoisoned(entry))) > ... > } > > ... > ... > > /* > * entry could be a migration/hwpoison entry at this point, so this > * check prevents the kernel from going below assuming that we have > * a active hugepage in pagecache. This goto expects the 2nd page fault, > * and is_hugetlb_entry_(migration|hwpoisoned) check will properly > * handle it. > */ > if (!pte_present(entry)) > goto out_mutex; > ... > } > > The code was designed to check for hwpoisoned/migration entries upfront, > and then bail out if further down the pte was not present anymore, relying > on the second fault to properly handle migration/hwpoison entries that > time around. > > The way we handle this is different nowadays, so drop the misleading > comment. > > Link: https://lkml.kernel.org/r/20250627102904.107202-5-osalvador@suse.de > Signed-off-by: Oscar Salvador > Cc: David Hildenbrand > Cc: Gavin Guo > Cc: Muchun Song > Cc: Peter Xu > Signed-off-by: Andrew Morton > --- Acked-by: David Hildenbrand -- Cheers, David / dhildenb