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(p200300d82f1af5004346f17c2bde808c.dip0.t-ipconnect.de. [2003:d8:2f1a:f500:4346:f17c:2bde:808c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b4708d0941sm12161694f8f.26.2025.07.08.01.07.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Jul 2025 01:07:27 -0700 (PDT) Message-ID: <6716889f-00c1-44db-a7e3-c58a68dcd6ae@redhat.com> Date: Tue, 8 Jul 2025 10:07:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 mm-new] mm: check if folio has valid mapcount before folio_test_{anon,ksm}() when necessary To: Harry Yoo , Andrew Morton Cc: Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Christoph Lameter , David Rientjes , Matthew Wilcox , linux-mm@kvack.org References: <20250707120740.4413-1-harry.yoo@oracle.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: <20250707120740.4413-1-harry.yoo@oracle.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 52sHac882HEaiQC2rQiWVcwXPPLftPWnVARnbimAYxM_1751962049 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: rspam03 X-Rspamd-Queue-Id: 9C0F3A0007 X-Stat-Signature: ksja3jsaqxg1f7dsm4b36chq3afa8rw6 X-Rspam-User: X-HE-Tag: 1751962051-900036 X-HE-Meta: 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 0lw9h45t 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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: > if (folio_test_anon(folio)) { > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 970600d79dac..00ba2c8b221e 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -706,12 +706,15 @@ PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted) > * address_space which maps the folio from disk; whereas "folio_mapped" > * refers to user virtual address space into which the folio is mapped. > * > - * For slab pages, since slab reuses the bits in struct page to store its > - * internal states, the folio->mapping does not exist as such, nor do > - * these flags below. So in order to avoid testing non-existent bits, > - * please make sure that folio_test_slab(folio) actually evaluates to > - * false before calling the following functions (e.g., folio_test_anon). > - * See mm/slab.h. > + * For certain typed pages like slabs, since they reuse bits in struct page > + * to store internal states, folio->mapping does not point to a valid > + * mapping, nor do these flags exist. To avoid testing non-existent bits, > + * make sure folio_has_mapcount() actually evaluates to true before calling > + * the following functions (e.g., folio_test_anon). > + * > + * The folio_has_mapcount() check can be skipped if the folio is mapped > + * to userspace, since a folio with !folio_has_mapcount() cannot be mapped > + * to userspace at all. > */ > #define FOLIO_MAPPING_ANON 0x1 > #define FOLIO_MAPPING_ANON_KSM 0x2 > @@ -1092,6 +1095,11 @@ static inline bool PageHuge(const struct page *page) > return folio_test_hugetlb(page_folio(page)); > } > > +static inline bool folio_has_mapcount(const struct folio *folio) > +{ > + return !page_has_type(&folio->page) || folio_test_hugetlb(folio); > +} > + I don't like the naming. The thing is, in the future only folios will have a mapcount. Asking whether a folio has a mapcount is asking the wrong question. It's rather, that we want to reject *pages* early, and not cast them to the folio in the first place. -- Cheers, David / dhildenb