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[2003:d8:2f03:5b00:f549:a879:b2d3:73ee]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-450d7fc29f4sm26949415e9.38.2025.05.30.13.37.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 30 May 2025 13:37:01 -0700 (PDT) Message-ID: <722b084a-872b-4694-963d-241d00c63487@redhat.com> Date: Fri, 30 May 2025 22:37:00 +0200 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] gup: optimize longterm pin_user_pages() for large folio To: lizhe.67@bytedance.com Cc: akpm@linux-foundation.org, jgg@ziepe.ca, jhubbard@nvidia.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, muchun.song@linux.dev, peterx@redhat.com References: <6f5e3238-9750-40db-8fe1-88d28655a988@redhat.com> <20250530150254.52362-1-lizhe.67@bytedance.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: <20250530150254.52362-1-lizhe.67@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 30.05.25 17:02, lizhe.67@bytedance.com wrote: > On Fri, 30 May 2025 15:08:06 +0200, david@redhat.com wrote: > >>>>> diff --git a/mm/gup.c b/mm/gup.c >>>>> index 84461d384ae2..8c11418036e2 100644 >>>>> --- a/mm/gup.c >>>>> +++ b/mm/gup.c >>>>> @@ -2317,6 +2317,25 @@ static void pofs_unpin(struct pages_or_folios *pofs) >>>>> unpin_user_pages(pofs->pages, pofs->nr_entries); >>>>> } >>>>> >>>>> +static struct folio *pofs_next_folio(struct folio *folio, >>>>> + struct pages_or_folios *pofs, long *index_ptr) >>>>> +{ >>>>> + long i = *index_ptr + 1; >>>>> + unsigned long nr_pages = folio_nr_pages(folio); >>>>> + >>>>> + if (!pofs->has_folios) >>>>> + while ((i < pofs->nr_entries) && >>>>> + /* Is this page part of this folio? */ >>>>> + (folio_page_idx(folio, pofs->pages[i]) < nr_pages)) >>>> >>>> passing in a page that does not belong to the folio looks shaky and not >>>> future proof. >>>> >>>> folio_page() == folio >>>> >>>> is cleaner >>> >>> Yes, this approach is cleaner. However, when obtaining a folio >>> corresponding to a page through the page_folio() interface, >> >> Right, I meant page_folio(). >> >>> READ_ONCE() is used internally to read from memory, which results >>> in the performance of pin_user_pages() being worse than before. >> >> See contig_pages in [1] how it can be done using folio_page(). >> >> [1] >> https://lore.kernel.org/all/20250529064947.38433-1-lizhe.67@bytedance.com/T/#u > > Thank you for your suggestion. It is indeed a good idea. I > initially thought along the same lines. However, I found that > the conditions for optimization here are slightly different > from those in contig_pages(). Here, it is only necessary to > ensure that the page is within the folio, rather than > requiring contiguity. Yes. > > I have made some preliminary attempts: using the method of > contig_pages() still gets an optimization effect of > approximately 73%. On the other hand, if we use the following > code to determine whether page_to_pfn(pofs->pages[i]) belongs > to the range > [folio_pfn(folio), folio_pfn(folio) + folio_nr_pages(folio)), > the optimization effect is about 70%. I sincerely hope to > hear your thoughts on which solution you might favor. > > +static struct folio *pofs_next_folio(struct folio *folio, > + struct pages_or_folios *pofs, long *index_ptr) > +{ > + long i = *index_ptr + 1; > + > + if (!pofs->has_folios) { > + unsigned long start_pfn = folio_pfn(folio); > + unsigned long end_pfn = start_pfn + folio_nr_pages(folio); > + > + for (; i < pofs->nr_entries; i++) { > + unsigned long pfn = page_to_pfn(pofs->pages[i]); > + > + /* Is this page part of this folio? */ > + if ((pfn < start_pfn) || (pfn >= end_pfn)) > + break; folio_page() is extremely efficient with CONFIG_SPARSEMEM_VMEMMAP. I am not sure how efficient it will be in the future once "struct folio" is no longer an overlay of "struct page". page_to_pfn() should be slightly more expensive than folio_page() right now, but maybe more efficient in the future (maybe). I don't particularly care, whatever you prefer :) -- Cheers, David / dhildenb