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[80.187.67.108]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5c42bb5f2b6sm3464989a12.52.2024.09.17.03.12.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Sep 2024 03:12:08 -0700 (PDT) Message-ID: <42d6f3db-33db-4475-97e3-fbd28ea131ea@redhat.com> Date: Tue, 17 Sep 2024 12:12:05 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Compute mTHP order efficiently To: Dev Jain , Matthew Wilcox Cc: akpm@linux-foundation.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, baohua@kernel.org, hughd@google.com, ioworker0@gmail.com, wangkefeng.wang@huawei.com, baolin.wang@linux.alibaba.com, gshan@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240913091902.1160520-1-dev.jain@arm.com> <091f517d-e7dc-4c10-b1ac-39658f31f0ed@arm.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: <091f517d-e7dc-4c10-b1ac-39658f31f0ed@arm.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: 7bit X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: D3B4B20011 X-Stat-Signature: a8q15i38nsn53jbht8zro64qa97ua1wb X-HE-Tag: 1726567932-928047 X-HE-Meta: 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 9NokxUTi qDq8fGeSJpNnNpJMZht3WLyMvSnOYNj0V5QFv+fmXloogOC3FL+P0bsBnf0HRo2IsPVKmaMTTRh/1wjNOe3nqu++3hN+oMtq3bzC+ntNWkEAUgpqmQzUvj38OensgsMjU1T4lUqJ90b85A+B9K0wA6Da23nGvst3DBbid+xd3MzpsWFr9rK4Y5pv01ZuszWJVYSs5R/jZ/wMCezKwrcohYAKKscpKSLEl2I1uVOSfT5VDPDA8c9KHKrVd7AIj08pm2GyRqscyfS03k1FsnK/kli/Ko0O9h0cSZLvw21vvX/Q2MDYLAByZwwWV4DuGtFc+emdYZXnhWeoATOqe8oWpiihWSMmKRBQ1vFrbOar7OGyUdIt+auqROk2yfv71YHtsFyJ9Rttfr2anWOtcGlt0WmRsskjkohyyGMpP 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 17.09.24 05:55, Dev Jain wrote: > > On 9/16/24 18:54, Matthew Wilcox wrote: >> On Fri, Sep 13, 2024 at 02:49:02PM +0530, Dev Jain wrote: >>> We use pte_range_none() to determine whether contiguous PTEs are empty >>> for an mTHP allocation. Instead of iterating the while loop for every >>> order, use some information, which is the first set PTE found, from the >>> previous iteration, to eliminate some cases. The key to understanding >>> the correctness of the patch is that the ranges we want to examine >>> form a strictly decreasing sequence of nested intervals. >> This is a lot more complicated. Do you have any numbers that indicate >> that it's faster? Yes, it's fewer memory references, but you've gone >> from a simple linear scan that's easy to prefetch to an exponential scan >> that might confuse the prefetchers. > > I do have some numbers, I tested with a simple program, and also used > ktime API, with the latter, enclosing from "order = highest_order(orders)" > till "pte_unmap(pte)" (enclosing the entire while loop), a rough average > estimate is that without the patch, it takes 1700 ns to execute, with the > patch, on an average it takes 80 - 100ns less. I cannot think of a good > testing program... And that is likely what Willy is actually wondering about: does it have any real world impact or is the benefit just noise. :) Change does not look too wild to me, but yes, it increases complexity. -- Cheers, David / dhildenb