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[2003:cb:c74b:e00:9c12:cdf2:bf1c:b8ed]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-371898498e1sm12527425f8f.41.2024.08.20.01.23.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 Aug 2024 01:23:57 -0700 (PDT) Message-ID: Date: Tue, 20 Aug 2024 10:23:56 +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> <73d5e928-e06d-416a-9de6-fb2d34da9095@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-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D776E2000D X-Stat-Signature: 6jsk97zrkd13dh3czeyd3kst5njfe55n X-HE-Tag: 1724142242-259420 X-HE-Meta: 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 17KSBjn/ ysaG92vO0S8n+7RGgEnXfoRWfoplch+f3jIKYNbpuKX/lKVbSXUWRJeYJgoFHriN+SHNwZIbFKallHzTfAvI9/8zkn93A3ZtQz6a4Am5DdlJ9CfrfhQbCg8aY+ES+JJgjC5Pia42k97vymqwicItYUJyLJZmnsiMB/ERYbgnDdSwRo/gf0zMAtIMqctdqyH9ZzJSfAph2z7Hv2aO5evbyyA3GJviBmruearcX2edGt+7gAqPvoIfQ1w5pPexSRr0Wk848TayWyZHaVch/K42Dt+WKMWZ/hF2vXYyUD8l6XPw2US/jzB2jYXt8rkEfdBP4Xybp7tq5F2VcGFUrssMJan9dMJuoasho4E30CPX1qWdhCGamTelhNlVZ5Rctrv4Giqfz+Vcmnj+ORyDqbb45fQjqB1Urk1WhBUPTwCkxhdcQjYo9c8xYqDo8IElk/VvQBU0V 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 20.08.24 10:22, Kefeng Wang wrote: > > > On 2024/8/19 21:27, David Hildenbrand wrote: >> 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()? > > Yes, the find_subpage only used under iov_iter_is_xarray(), and > only afs/erofs/netfs/orangefs/ceph/smb use ITER_XARRAY, no hugetlb > involved, so we could safety drop hugetlb part in find_subpage(). Highlighting that in the patch description would likely be best. The hugetlb check is essentially dead code right now ... and confuses David :) -- Cheers, David / dhildenb