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[178.24.249.8]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a83838cfb74sm636786966b.66.2024.08.19.06.27.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 19 Aug 2024 06:27:18 -0700 (PDT) Message-ID: <73d5e928-e06d-416a-9de6-fb2d34da9095@redhat.com> Date: Mon, 19 Aug 2024 15:27:17 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/5] mm: remove find_subpage() To: Kefeng Wang , Andrew Morton Cc: Matthew Wilcox , Alexander Viro , Sidhartha Kumar , linux-mm@kvack.org References: <20240817095122.2460977-1-wangkefeng.wang@huawei.com> <20240817095122.2460977-2-wangkefeng.wang@huawei.com> <646f8a48-820f-40ae-bf96-7d554bf4493a@huawei.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: <646f8a48-820f-40ae-bf96-7d554bf4493a@huawei.com> 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-Rspam-User: X-Rspamd-Queue-Id: 5F6C540015 X-Rspamd-Server: rspam01 X-Stat-Signature: 6us6aacyfe1my3wos4dm15dwgdspgxt9 X-HE-Tag: 1724074043-658201 X-HE-Meta: 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 IyYdfgyo 1dQ48mNfthz2QROnT3poOuaU+T9OiywYrd/sXbdwFMktHyIf6MKrnziv1gxW2evzs5yuMxHbvQV8rz6RyEZEUnwyrAxy7W3U8MRmuzuWbXa8O5Hss2yRK7Y80TC4jwqAvYHuSW3TuW8JLU/+ZQO1nGljkSx8RvluY6KhYmTQwfo1LFq0pY2pKxfL2A62QbMvtF6yl8cZ8WIH79WmJ4Ut9464bJ+T9ln/VUNP3vYhEKIck9yocmlc2XDMouPVr6aklc48cUIA2o5TMyjgQ4s7Zhcazgsi4DteaK660xTHSJhcJ+qLPB/NWl9cDh82vU/IUQpscwYLqMXB8xhgRhfECjjy4YJkssb7Rx7rG0k3EUa9mO5kLNAWWWkeFHkn2H3dxXpYWnQG9+h75k8KPcNQl8GkvBtXOnA5OdzMM 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 19.08.24 13:02, Kefeng Wang wrote: > > > On 2024/8/17 17:51, Kefeng Wang wrote: >> After commit a08c7193e4f1 ("mm/filemap: remove hugetlb special casing >> in filemap.c"), the find_subpage() should remove hugetlb case as the >> folio_file_page(), furthermore, we could convert to use folio_file_page() >> to remove find_subpage(). > > There are some comments from David to the non-public send(forget to cc > list), > the problem of find_subpage() is not described , so adding some here, > Thanks! > > see commit a08c7193e4f1, > > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -789,9 +789,6 @@ static inline pgoff_t folio_next_index(struct folio > *folio) > */ > static inline struct page *folio_file_page(struct folio *folio, > pgoff_t index) > { > - /* HugeTLBfs indexes the page cache in units of hpage_size */ > - if (folio_test_hugetlb(folio)) > - return &folio->page; > return folio_page(folio, index & (folio_nr_pages(folio) - 1)); > } > > It changes the granularity of ->index to the base page size rather than > the huge page size, so for hugetlb, the special handling(return head > page) is removed from folio_file_page(), so we need remove special > hugetlb handling find_subpage() too, maybe this is a bugfix as a > separate patch. That's the part I understand. Any caller of folio_file_page() is expected to be able to deal with a hugetlb tail page after this patch. Now, your assumption is the callers of find_subpage() are find with a tail page as well. That's the part I am not sure about, but if you think all callers are fine, then please spell that out in the patch description. Something like "Note that find_subpage() would never return the tail page of a hugetlb folio, but folio_file_page() will return tail pages. This, however, is fine because XYZ". But I am wondering if these functions here even get called for hugetlb ever ... :) They only trigger for iov_iter_is_xarray()? > > And after removing hugetlb handling in find_subpage(), there is > another issue about "head + (index & (thp_nr_pages(head) - 1))", for > hugetlb without sparsemem vmemmap, struct page is not guaranteed to be > contiguous beyond a section, so we need to use > > nth_page(head, (index & (thp_nr_pages(head) - 1)) Agreed. So as soon as we would unlock that code for THP, we would run into that issue. > > and in order to reduce code maintain between folio_file_page() and > find_subpage()， just use folio_file_page() in find_subpage() to > fix above two issue. > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index d9c7edb6422b..e2553e4ac3ef 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -866,11 +866,9 @@ static inline bool folio_contains(struct folio > *folio, pgoff_t index) > */ > static inline struct page *find_subpage(struct page *head, pgoff_t index) > { > - /* HugeTLBfs wants the head page regardless */ > - if (PageHuge(head)) > - return head; > + struct folio *folio = (struct folio *)head; > > - return head + (index & (thp_nr_pages(head) - 1)); > + return folio_file_page(folio); ^ I assume you meant "folio_file_page(folio, index);" > } > > And this will correctly handle head/tail page, correct me if I am wrong. Right. Is iov_iter_xarray() one of the things Willy mentioned is scheduled for removal? Then I agree that looking into removing that part completely does also sounds reasonable. -- Cheers, David / dhildenb