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[2003:cb:c706:2000:e44c:bc46:d8d3:be5]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4395a1aa7e8sm255279355e9.26.2025.02.20.12.45.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Feb 2025 12:45:02 -0800 (PST) Message-ID: <70971ae0-3933-4e55-983a-24c6b65ef913@redhat.com> Date: Thu, 20 Feb 2025 21:45:00 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/4] mm: page_ext: add an iteration API for page extensions To: Luiz Capitulino , linux-kernel@vger.kernel.org, linux-mm@kvack.org, yuzhao@google.com, pasha.tatashin@soleen.com Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, muchun.song@linux.dev References: <3f0e058aef3951b39cf6bb4259c247352d4fe736.1739931468.git.luizcap@redhat.com> <4cb93166-29fd-4aea-965b-5dfb62d4dc8c@redhat.com> <0a8bd481-0b97-416d-935e-84828016445d@redhat.com> From: David Hildenbrand Content-Language: en-US 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: <0a8bd481-0b97-416d-935e-84828016445d@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit >>> +    for (__iter.index = 0;                                 \ >>> +        __page_ext && __iter.index < __pgcount;        \ >>> +        __page_ext = page_ext_iter_next(&__iter),      \ >>> +        __iter.index++) >> >> Hm, if we now have an index, why not turn iter.pfn -> iter.start_pfn, and only adjust the index in page_ext_iter_next? >> >> Then you can set the index to 0 in page_ext_iter_begin() and have here >> >> for (__page_ext = page_ext_iter_begin(&__iter, __page), >>      __page_ext && __iter.index < __pgcount, >>      __page_ext = page_ext_iter_next(&__iter);) > > I can do this if you feel strong about it, but I prefer explicitly over > implicitly. I moved the index into the iter object just to avoid having > to define it in the macro's body. Also, the way I did it allows for > using page_ext_iter_begin()/page_ext_iter_next() own their if the need > arises. Ah, I see what you mean. for (__page_ext = page_ext_iter_begin(&__iter, __page, __pgcount); __page_ext; __page_ext = page_ext_iter_next(&__iter)) Could do that I guess by moving the count in there as well and performing the check+increment in page_ext_iter_next. That looks very clean to me, but no strong opinion. Having the index in there just to make a macro happy is rather weird. > >> A page_ext_iter_reset() could then simply reset the index=0 and >> lookup the page_ext(start_pfn + index) == page_ext(start_pfn) > > Just note we don't have page_ext_iter_reset() today (and I guess it's > not needed). Right, was writing this before reviewing the other patch. > >>> + >>> +/** >>> + * for_each_page_ext_order(): iterate through page_ext objects >>> + *                            for a given page order >>> + * @__page: the page we're interested in >>> + * @__order: page order to iterate through >>> + * @__page_ext: struct page_ext pointer where the current page_ext >>> + *              object is returned >>> + * @__iter: struct page_ext_iter object (defined in the stack) >>> + * >>> + * IMPORTANT: must be called with RCU read lock taken. >>> + */ >>> +#define for_each_page_ext_order(__page, __order, __page_ext, __iter) \ >>> +    for_each_page_ext(__page, (1UL << __order), __page_ext, __iter) >>> + >>>   #else /* !CONFIG_PAGE_EXTENSION */ >>>   struct page_ext; >>> diff --git a/mm/page_ext.c b/mm/page_ext.c >>> index 641d93f6af4c1..508deb04d5ead 100644 >>> --- a/mm/page_ext.c >>> +++ b/mm/page_ext.c >>> @@ -549,3 +549,44 @@ void page_ext_put(struct page_ext *page_ext) >>>       rcu_read_unlock(); >>>   } >>> + >>> +/** >>> + * page_ext_iter_begin() - Prepare for iterating through page extensions. >>> + * @iter: page extension iterator. >>> + * @page: The page we're interested in. >>> + * >>> + * Must be called with RCU read lock taken. >>> + * >>> + * Return: NULL if no page_ext exists for this page. >>> + */ >>> +struct page_ext *page_ext_iter_begin(struct page_ext_iter *iter, struct page *page) >>> +{ >>> +    iter->pfn = page_to_pfn(page); >>> +    iter->page_ext = lookup_page_ext(page); >>> + >>> +    return iter->page_ext; >>> +} >>> + >>> +/** >>> + * page_ext_iter_next() - Get next page extension >>> + * @iter: page extension iterator. >>> + * >>> + * Must be called with RCU read lock taken. >>> + * >>> + * Return: NULL if no next page_ext exists. >>> + */ >>> +struct page_ext *page_ext_iter_next(struct page_ext_iter *iter) >>> +{ >>> +    if (WARN_ON_ONCE(!iter->page_ext)) >>> +        return NULL; >>> + >>> +    iter->pfn++; >> > +> +    if (page_ext_iter_next_fast_possible(iter->pfn)) { >>> +        iter->page_ext = page_ext_next(iter->page_ext); >>> +    } else { >>> +        iter->page_ext = lookup_page_ext(pfn_to_page(iter->pfn)); >>> +    } >>> + >>> +    return iter->page_ext; >>> +} >> >> We now always have a function call when calling into page_ext_iter_next(). Could we move that to the header and rather expose lookup_page_ext() ? > > I personally don't like over-using inline functions, also I don't think this > code needs optimization since the current clients make the affected code paths > slow anyways (and this also applies to the likely/unlikely use in page_owner > and page_table_check, I'd drop all of them if you ask me). But again, I can > change if this would prevent you from giving your ACK :) Well, 512^512 function calls for a 1 GiB page just to traverse the page ext? :) -- Cheers, David / dhildenb