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[2003:cb:c706:3100:19a8:d898:8e69:6aff]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-421581016e0sm14760855e9.9.2024.06.05.02.41.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Jun 2024 02:41:25 -0700 (PDT) Message-ID: <776de760-e817-43b2-bd00-8ce96f4e37a8@redhat.com> Date: Wed, 5 Jun 2024 11:41:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup: don't check page lru flag before draining it To: yangge1116 , akpm@linux-foundation.org, Matthew Wilcox Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, baolin.wang@linux.alibaba.com, liuzixing@hygon.cn References: <1717498121-20926-1-git-send-email-yangge1116@126.com> <0d7a4405-9a2e-4bd1-ba89-a31486155233@redhat.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: 8bit X-Stat-Signature: gc7mooh9jk5mzqfj1dd14aezwatybgip X-Rspamd-Queue-Id: 129DD40003 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1717580489-172244 X-HE-Meta: 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 cp0GfHMP DHmSK9A2LEZU3dB6+/SXg48omHHRHcWj2to3gMklpO0pEZ58DqIkrrKqyLrfJH8uKMcvWWaL0CWJkpvEt83QtClkwY8sZHQcZrPZnVhKY0E2aXfODGPF8OSnI0UpnfAVCMltZVY7hfAKTbK7iWakKQe1UtkPFkbV//jmz+7s4wEVtZURCgbplP9vJmXrklGulHpCBmsbrapGMuERCAKhsYROEcKuTD0VRFComvXfzRtiEpd8FYmxnxQcTT8/r3tgZGE0wYBHhgJowR/12nUKJaYTRubs1+zSzhny0U6c/b1jGbqaAaSheuL2WMAE/ygM6MrEPSzbz770Qp1ccRjIdMSZifphSkDs9uj+xR9rk7YBWy8heSuVlLPa9QYYmrXqYQUMUxL4i7xcUEjUShPQOARx35KcfnB99LcK/4o3YjyPhzyEfXWJHDvXQQDc5DUjQyn7K+VeiGgCofHLfit2MUGKkhO2dnm5D/5W1Vh6iyYtbreHbNs/rCg30meTmJMXZwK0swoP7wciPHtWO9W0+Y6EwCA== 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 05.06.24 03:18, yangge1116 wrote: > > > 在 2024/6/4 下午9:47, David Hildenbrand 写道: >> On 04.06.24 12:48, yangge1116@126.com wrote: >>> From: yangge >>> >>> If a page is added in pagevec, its ref count increases one, remove >>> the page from pagevec decreases one. Page migration requires the >>> page is not referenced by others except page mapping. Before >>> migrating a page, we should try to drain the page from pagevec in >>> case the page is in it, however, folio_test_lru() is not sufficient >>> to tell whether the page is in pagevec or not, if the page is in >>> pagevec, the migration will fail. >>> >>> Remove the condition and drain lru once to ensure the page is not >>> referenced by pagevec. >> >> What you are saying is that we might have a page on which >> folio_test_lru() succeeds, that was added to one of the cpu_fbatches, >> correct? > > Yes > >> >> Can you describe under which circumstances that happens? >> > > If we call folio_activate() to move a page from inactive LRU list to > active LRU list, the page is not only in LRU list, but also in one of > the cpu_fbatches. > > void folio_activate(struct folio *folio) > { > if (folio_test_lru(folio) && !folio_test_active(folio) && > !folio_test_unevictable(folio)) { > struct folio_batch *fbatch; > > folio_get(folio); > //After this, folio is in LRU list, and its ref count have > increased one. > > local_lock(&cpu_fbatches.lock); > fbatch = this_cpu_ptr(&cpu_fbatches.activate); > folio_batch_add_and_move(fbatch, folio, folio_activate_fn); > local_unlock(&cpu_fbatches.lock); > } > } Interesting, the !SMP variant does the folio_test_clear_lru(). It would be really helpful if we could reliably identify whether LRU batching code has a raised reference on a folio. We have the same scenario in * folio_deactivate() * folio_mark_lazyfree() In folio_batch_move_lru() we do the folio_test_clear_lru(folio). No expert on that code, I'm wondering if we could move the folio_test_clear_lru() out, such that we can more reliably identify whether a folio is on the LRU batch or not. -- Cheers, David / dhildenb