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[2003:cb:c709:a00:7d7d:3665:5fe4:7127]) by smtp.gmail.com with ESMTPSA id z5-20020a5d44c5000000b0033b87c2725csm408427wrr.104.2024.03.14.03.26.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 Mar 2024 03:26:18 -0700 (PDT) Message-ID: Date: Thu, 14 Mar 2024 11:26:17 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm: Turn folio_test_hugetlb into a PageType To: "Matthew Wilcox (Oracle)" , Andrew Morton Cc: linux-mm@kvack.org, Oscar Salvador , Miaohe Lin References: <20240314012506.1600378-1-willy@infradead.org> <20240314012506.1600378-2-willy@infradead.org> 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: <20240314012506.1600378-2-willy@infradead.org> 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-Rspamd-Queue-Id: 666BF180013 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: ibnogq6mms7airyg3ctdzkosuyb59zhd X-HE-Tag: 1710411985-188582 X-HE-Meta: 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 P1YfM5tK PsE4vITy3pPfa2G9ZlygkDFEV+d5sxhVQm1WlfZ/JPnIhoojYB91veBt9d7wFamA8v11dp8/oI1qRzM2gU4J6fOnfd8W7QijPZjc4E9VBwDDbv8aHD8MUjJi4In1KfIX3jeh8DOyg+b1Gn5yDm/D47N1QQvPwpEEEsivOkSkydivFkLXnXi/S3TPoEACaZ2//m3xXIzQuYn0Ti7vpwYOreaoj4A== 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 14.03.24 02:25, Matthew Wilcox (Oracle) wrote: > The current folio_test_hugetlb() can be fooled by a concurrent folio split > into returning true for a folio which has never belonged to hugetlbfs. > This can't happen if the caller holds a refcount on it, but we have a > few places (memory-failure, compaction, procfs) which do not and should > not take a speculative reference. > > Since hugetlb pages do not use individual page mapcounts (they are always > fully mapped and use the entire_mapcount field to record the number of > mappings), the PageType field is available for use with only a minor > modification to page_mapcount() to ignore the value in this field for > hugetlb pages. Other parts of the kernel which examine page->_mapcount > directly already know about page_has_type() (eg procfs, dump_page()). > > Signed-off-by: Matthew Wilcox (Oracle) > --- Should we include this hunk: diff --git a/mm/debug.c b/mm/debug.c index c1c1a6a484e4c..f521e17150a10 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -63,7 +63,8 @@ static void __dump_folio(struct folio *folio, struct page *page, * encode own info, and we must avoid calling page_folio() again. */ if (!folio_test_slab(folio)) { - mapcount = atomic_read(&page->_mapcount) + 1; + if (!folio_test_hugetlb(folio)) + mapcount = atomic_read(&page->_mapcount) + 1; if (folio_test_large(folio)) mapcount += folio_entire_mapcount(folio); } Apart from that, LGTM Reviewed-by: David Hildenbrand -- Cheers, David / dhildenb