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[2003:d8:2f28:7800:30d7:645a:7306:e437]) by smtp.gmail.com with ESMTPSA id v21-20020a05600c471500b0040836519dd9sm6376006wmo.25.2023.12.01.12.06.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Dec 2023 12:06:23 -0800 (PST) Message-ID: <2d691c11-fa97-4f56-a4c4-c7f466c81d3a@redhat.com> Date: Fri, 1 Dec 2023 21:06:22 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/rmap: Fix misplaced parenthesis of a likely() To: Steven Rostedt , LKML , linux-mm@kvack.org Cc: Vlastimil Babka , Andrew Morton References: <20231201145936.5ddfdb50@gandalf.local.home> 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: <20231201145936.5ddfdb50@gandalf.local.home> 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-Queue-Id: A85E640027 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 8umrogju8jeohzfwmci9hcudpzqwi3ct X-HE-Tag: 1701461189-522683 X-HE-Meta: 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 Fl+FlKOu 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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 01.12.23 20:59, Steven Rostedt wrote: > From: Steven Rostedt (Google) > > Running my yearly branch profiler to see where likely/unlikely annotation > may be added or removed, I discovered this: > > correct incorrect % Function File Line > ------- --------- - -------- ---- ---- > 0 457918 100 page_try_dup_anon_rmap rmap.h 264 > [..] > 458021 0 0 page_try_dup_anon_rmap rmap.h 265 > That looks like a handy tool! > I thought it was interesting that line 264 of rmap.h had a 100% incorrect > annotation, but the line directly below it was 100% correct. Looking at the > code: > > if (likely(!is_device_private_page(page) && > unlikely(page_needs_cow_for_dma(vma, page)))) > > It didn't make sense. The "likely()" was around the entire if statement > (not just the "!is_device_private_page(page)"), which also included the > "unlikely()" portion of that if condition. Yes, that was clearly misplaced. > > If the unlikely portion is unlikely to be true, that would make the entire > if condition unlikely to be true, so it made no sense at all to say the > entire if condition is true. > > What is more likely to be likely is just the first part of the if statement > before the && operation. It's likely to be a misplaced parenthesis. And > after making the if condition broken into a likely() && unlikely(), both > now appear to be correct! > Reviewed-by: David Hildenbrand But > Cc: stable@vger.kernel.org stable, really? Why? > Fixes:fb3d824d1a46c ("mm/rmap: split page_dup_rmap() into page_dup_file_rmap() and page_try_dup_anon_rmap()") and does it even fix a real bug? -- Cheers, David / dhildenb