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[2003:cb:c70d:1f00:7a4e:8f21:98db:baef]) by smtp.gmail.com with ESMTPSA id o12-20020a5d684c000000b0034aa1e534c2sm11277902wrw.96.2024.04.24.02.40.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Apr 2024 02:40:09 -0700 (PDT) Message-ID: Date: Wed, 24 Apr 2024 11:40:07 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 06/18] mm: make folio_mapcount() return 0 for small typed folios To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-doc@vger.kernel.org, cgroups@vger.kernel.org, linux-sh@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , "Matthew Wilcox (Oracle)" , Peter Xu , Ryan Roberts , Yin Fengwei , Yang Shi , Zi Yan , Jonathan Corbet , Hugh Dickins , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , Chris Zankel , Max Filippov , Muchun Song , Miaohe Lin , Naoya Horiguchi , Richard Chang References: <20240409192301.907377-1-david@redhat.com> <20240409192301.907377-7-david@redhat.com> From: David Hildenbrand Content-Language: en-US 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: <20240409192301.907377-7-david@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 09.04.24 21:22, David Hildenbrand wrote: > We already handle it properly for large folios. Let's also return "0" > for small typed folios, like page_mapcount() currently would. > > Consequently, folio_mapcount() will never return negative values for > typed folios, but may return negative values for underflows. > > Signed-off-by: David Hildenbrand > --- > include/linux/mm.h | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index daf687f0e8e5..d453232bba62 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1260,12 +1260,19 @@ static inline int folio_large_mapcount(const struct folio *folio) > * references the entire folio counts exactly once, even when such special > * page table entries are comprised of multiple ordinary page table entries. > * > + * Will report 0 for pages which cannot be mapped into userspace, such as > + * slab, page tables and similar. > + * > * Return: The number of times this folio is mapped. > */ > static inline int folio_mapcount(const struct folio *folio) > { > - if (likely(!folio_test_large(folio))) > - return atomic_read(&folio->_mapcount) + 1; > + int mapcount; > + > + if (likely(!folio_test_large(folio))) { > + mapcount = atomic_read(&folio->_mapcount); > + return page_type_has_type(mapcount) ? 0 : mapcount + 1; > + } > return folio_large_mapcount(folio); > } > From 98acfb7ff35cb65fcfca5e799bf58f8afe84a645 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Wed, 24 Apr 2024 10:56:17 +0200 Subject: [PATCH] !fixup: mm: make folio_mapcount() return 0 for small typed folios Just like page_mapcount(), let's make folio_mapcount() slightly more efficient. Signed-off-by: David Hildenbrand --- include/linux/mm.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index cf700c5cdd58b..78e583b50e421 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1271,8 +1271,11 @@ static inline int folio_mapcount(const struct folio *folio) int mapcount; if (likely(!folio_test_large(folio))) { - mapcount = atomic_read(&folio->_mapcount); - return page_type_has_type(mapcount) ? 0 : mapcount + 1; + mapcount = atomic_read(&folio->_mapcount) + 1; + /* Handle page_has_type() pages */ + if (mapcount < PAGE_MAPCOUNT_RESERVE + 1) + mapcount = 0; + return mapcount; } return folio_large_mapcount(folio); } -- 2.44.0 -- Cheers, David / dhildenb