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[2003:d8:2f4f:2b00:69b5:3684:56c:6dd5]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-422870e9193sm94316495e9.21.2024.06.14.04.10.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Jun 2024 04:10:03 -0700 (PDT) Message-ID: Date: Fri, 14 Jun 2024 13:10:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 3/3] mm: remove folio_test_anon(folio)==false path in __folio_add_anon_rmap() To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, chrisl@kernel.org, linux-kernel@vger.kernel.org, mhocko@suse.com, ryan.roberts@arm.com, baolin.wang@linux.alibaba.com, yosryahmed@google.com, shy828301@gmail.com, surenb@google.com, v-songbaohua@oppo.com, willy@infradead.org, ying.huang@intel.com, yuzhao@google.com References: <20240613000721.23093-1-21cnbao@gmail.com> <20240613000721.23093-4-21cnbao@gmail.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-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 9155010002B X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: ebyep6dzpnsrf5huqaseggrt3kymogbk X-HE-Tag: 1718363407-142997 X-HE-Meta: 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 LYT11HpX p7UPbhMBJBuCHHX1t4+d4N2mNQVPWMGK+KkOhnKukCww5jBeEGqqSp2ZiemNMhAsKTq1GOvO0dPGAA0xW9d6yAl6XCXhBG8Wfm2C1S/MLoU1zviziHrFV9yeWm6GwXmtTd0LixSzzv+z1KOJAM8zHW/LFONq81AnH3uwuQRRrlB0VOFayB+uMYUnqwWfsT00+dYx9y/g7yvJ1z7EaoOADHkZ4bs6s9QW/wQSz9vDvf88Fe1Uf1TKsfrLDmAyu2OOmVchodEk7vvbSzobFHd6179v5ltKJaQsLl2b6csWu7SDWrZ5d5tb5S3MAxmwP8y06CxBw0EqMbFgh6jiwzF0OMjvRQp78vVTksZ5Tmk/UYb5L+aROCafDelbbkzFFIvtyJ8/5NwLbPeuGUaxuWenEz9sHehCLp4Svpb8W3G06jvj1l00= 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: >> I don't think that is required? We are only working with anon folios. Or >> were you able to trigger this? (which would be weird) > > I didn't trigger this. but I am not sure if kfifo is always anon based on > the code context. > > for page, it is 100% anon(otherwise "goto out"), but I am not quite > sure about kpage > by the code context. > > static int try_to_merge_one_page(struct vm_area_struct *vma, > struct page *page, struct page *kpage) > { > pte_t orig_pte = __pte(0); > int err = -EFAULT; > > if (page == kpage) /* ksm page forked */ > return 0; > > if (!PageAnon(page)) > goto out; > .... > } > > Then I saw this > > static int replace_page(struct vm_area_struct *vma, struct page *page, > struct page *kpage, pte_t orig_pte) > { > ... > VM_BUG_ON_PAGE(PageAnonExclusive(page), page); > VM_BUG_ON_FOLIO(folio_test_anon(kfolio) && PageAnonExclusive(kpage), > kfolio); > } > > If kfolio is always anon, we should have used > VM_BUG_ON_FOLIO(PageAnonExclusive(kpage), folio) > just like > VM_BUG_ON_PAGE(PageAnonExclusive(page), page); > without "folio_test_anon(kfolio)". > > So I lost my way. try_to_merge_one_page() is either called with a KSM page (anon) from try_to_merge_with_ksm_page() or with the shared zeropage (!anon and must never become anon) from cmp_and_merge_page(). So in replace_page(), we either have an ksm/anon page or the shared zeropage. We never updated the documentation of replace_page() to spell out that "kpage" can also be the shared zeropage. Note how replace_page() calls folio_add_anon_rmap_pte() not for the shared zeropage. If we would have to craft a new anon page things would be going terribly wrong. So not, this (!anon -> anon) must not happen and if it were to happen, it would be a real bug and your check in folio_add_anon_rmap_pte() would catch it. -- Cheers, David / dhildenb