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[2003:d8:2f44:3e00:9fca:7d89:a265:56f3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45a1d200fe6sm6366685e9.10.2025.08.13.23.54.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 Aug 2025 23:54:45 -0700 (PDT) Message-ID: Date: Thu, 14 Aug 2025 08:54:44 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 1/5] mm: introduce num_pages_contiguous() To: lizhe.67@bytedance.com, alex.williamson@redhat.com, jgg@nvidia.com Cc: torvalds@linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, farman@linux.ibm.com, Jason Gunthorpe References: <20250814064714.56485-1-lizhe.67@bytedance.com> <20250814064714.56485-2-lizhe.67@bytedance.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250814064714.56485-2-lizhe.67@bytedance.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 71Jbnrk339W38vhFCy63QCz3HtA16GIXr0qb9fcreSY_1755154487 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: D4E884000E X-Stat-Signature: nxmdz16xxufiwg5uaehmj9xod5gufd76 X-Rspam-User: X-HE-Tag: 1755154489-677585 X-HE-Meta: U2FsdGVkX197rNsU7cN3TDkkrsnIjRw5dpHiqevd1Bp0PXY3er3G11KVAQEkjC+pyG8tuZ23QPUo/RTJo/ikErGB+uiX0VW7F7fySeV16CKBsZ4y/dIfuRWQAb5zJGmPJVVRzyMrVYJRGkQp4ssOX/jMqV+0yviZHdBgBWjcZg9ftVl2t0/D3P30/8yIF+Q3kU53xlSsSo7SDTnwl5QE+D3wU5T3tQCEjMXSx3hKbbKQnmj4gJee8xwtgWyC8Gl4dRVMVZcPupbQyhQuFET4xokApCmo6TBa6oI0q435W6Bg6FoEQx2wa24XNXeqTU0PrCFvrnc8VAQNnm8O2kRVyOY19mu9MtzMtO5z3tzYtiWpdu9X5ZCoGvQQObjnts1JFCTGbag+yedvrwn7ipRSvkxzVPIUweTvJZVpeDhj5cFIv08pF+4MSkRccvwptOxUNODoEnj0oEOO+Q1RqQenNDrgumNHkbEAjdfOS4bvoRJEwcTvFOXEqFEQ35rean3exPfZG/3zwXDCTvYEx2VOhpzhM0ZMAsM8/BZIe13QYtUThDwt3cVnO8yG8/Lst0XsqSGZsO4FQd4BtimFqGgveiS6YQuW6U4mDJeJZ9ksEyYIxHhs2qpkJZaoYwSowXQKsuvq+lzDJNExXPFR+354VoCLVZ3Mjs2dV3q3huMvGSZ/4GJslLClTTX0ZDRuqLbhOXwJPqJrDm+Mdf1dT5/ZmzjBXlItCnUQ03ywXPjvXc5aS3QQ7c2tzEwcJwt9zO4lqHyx1cAugi0K1u7KrsR/qoJ52NxeJVZsQxExmPyqpn6MkYMmymBecbNYNlkrP/lQyXgcrSptg3WdoRxVa7RNmW31dk+UIJY38fYF7rvGBYTHdZqqL7XFxuZZoFpOItFtkXax4ISi06nZJnqXo22N6QhASpXerPkguWZeGtAg+EHuyeFDtAFHFOA+pgn8nj7+aiJZ4PzqY15j/MzV2CA SZ1iZt9a 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 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 14.08.25 08:47, lizhe.67@bytedance.com wrote: > From: Li Zhe > > Let's add a simple helper for determining the number of contiguous pages > that represent contiguous PFNs. > > In an ideal world, this helper would be simpler or not even required. > Unfortunately, on some configs we still have to maintain (SPARSEMEM > without VMEMMAP), the memmap is allocated per memory section, and we might > run into weird corner cases of false positives when blindly testing for > contiguous pages only. > > One example of such false positives would be a memory section-sized hole > that does not have a memmap. The surrounding memory sections might get > "struct pages" that are contiguous, but the PFNs are actually not. > > This helper will, for example, be useful for determining contiguous PFNs > in a GUP result, to batch further operations across returned "struct > page"s. VFIO will utilize this interface to accelerate the VFIO DMA map > process. > > Implementation based on Linus' suggestions to avoid new usage of > nth_page() where avoidable. > > Suggested-by: Linus Torvalds > Suggested-by: Jason Gunthorpe > Signed-off-by: Li Zhe > Co-developed-by: David Hildenbrand > Signed-off-by: David Hildenbrand > --- > include/linux/mm.h | 7 ++++++- > include/linux/mm_inline.h | 35 +++++++++++++++++++++++++++++++++++ > 2 files changed, 41 insertions(+), 1 deletion(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 1ae97a0b8ec7..ead6724972cf 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1763,7 +1763,12 @@ static inline unsigned long page_to_section(const struct page *page) > { > return (page->flags >> SECTIONS_PGSHIFT) & SECTIONS_MASK; > } > -#endif > +#else /* !SECTION_IN_PAGE_FLAGS */ > +static inline unsigned long page_to_section(const struct page *page) > +{ > + return 0; > +} > +#endif /* SECTION_IN_PAGE_FLAGS */ > > /** > * folio_pfn - Return the Page Frame Number of a folio. > diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h > index 89b518ff097e..5ea23891fe4c 100644 > --- a/include/linux/mm_inline.h > +++ b/include/linux/mm_inline.h > @@ -616,4 +616,39 @@ static inline bool vma_has_recency(struct vm_area_struct *vma) > return true; > } > > +/** > + * num_pages_contiguous() - determine the number of contiguous pages > + * that represent contiguous PFNs > + * @pages: an array of page pointers > + * @nr_pages: length of the array, at least 1 > + * > + * Determine the number of contiguous pages that represent contiguous PFNs > + * in @pages, starting from the first page. > + * > + * In kernel configs where contiguous pages might not imply contiguous PFNs > + * over memory section boundaries, this function will stop at the memory > + * section boundary. Jason suggested here instead: " In some kernel configs contiguous PFNs will not have contiguous struct pages. In these configurations num_pages_contiguous() will return a smaller than ideal number. The caller should continue to check for pfn contiguity after each call to num_pages_contiguous(). " -- Cheers David / dhildenb