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[2003:cb:c710:8800:a73c:ec5b:c02c:5e0b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4215c19d52dsm33484935e9.8.2024.06.06.13.21.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Jun 2024 13:21:53 -0700 (PDT) Message-ID: Date: Thu, 6 Jun 2024 22:21:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] selftests/mm: use volatile keyword to not optimize mmap read variable To: "Pankaj Raghav (Samsung)" Cc: Shuah Khan , Andrew Morton , willy@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, gost.dev@samsung.com, mcgrof@kernel.org, linux-kselftest@vger.kernel.org, Zi Yan , Pankaj Raghav References: <20240606135835.600022-1-kernel@pankajraghav.com> <5b4e7ef2-3ced-4d4a-989c-e99b06598d32@redhat.com> <20240606201831.ywmawi7xl6jgj3p4@quentin> 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: <20240606201831.ywmawi7xl6jgj3p4@quentin> 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: rspam05 X-Rspamd-Queue-Id: 2464E20004 X-Stat-Signature: 4oxkc7u35f5ssxe8mo5mdit77es7ssxi X-Rspam-User: X-HE-Tag: 1717705319-727387 X-HE-Meta: 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 zipINVub bV2vFj5DMwx1hqVl/MUJkrdCLnmKpPvoizJNsLg39yEHzU4p9Ygg/FVV/Elpz8xeHSiN1mYtziIYps6t9jV1eR5xHT0nX+0EbHIZh5earww1J1zwHiM3IykzxKbRryuOHWjggcU60yScGeGJJ2Q+tyCsI3VlSOpsLFU7305Wui6Sy5pQbBTLPilLyWnUjaDzg02xafOzV2KjouRl7MCZrMmgMTFraregls9qKbUb91r2yk4ueAoL+egBe0S5fA0Sd/jVRgl7cF2d9dzHbyWviy75wGl1qOMvyDvJ7myoc1AHVDbnG+KvvGLcDzhQzvITgiPjt01nx1LwxVAxJA6weJLMoP4CdB3mB4sGHg274eBCFijtqlyJqe6El7Ykx39uhYHKGRv9IogEi0cQ1eMD9cgEUghrXpuz0UdXojS0RCNgqw9Cl3Yx4ZCd6Qbn1d/IkiVXt 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 06.06.24 22:18, Pankaj Raghav (Samsung) wrote: > On Thu, Jun 06, 2024 at 05:57:21PM +0200, David Hildenbrand wrote: >> On 06.06.24 17:56, David Hildenbrand wrote: >>> On 06.06.24 15:58, Pankaj Raghav (Samsung) wrote: >>>> From: Pankaj Raghav >>>> >>>> create_pagecache_thp_and_fd() in split_huge_page_test.c used the >>>> variable dummy to perform mmap read. >>>> >>>> However, this test was skipped even on XFS which has large folio >>>> support. The issue was compiler (gcc 13.2.0) was optimizing out the >>>> dummy variable, therefore, not creating huge page in the page cache. >>>> >>>> Add volatile keyword to force compiler not to optimize out the loop >>>> where we read from the mmaped addr. >>>> >>>> Signed-off-by: Pankaj Raghav >>>> --- >>>> tools/testing/selftests/mm/split_huge_page_test.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c >>>> index d3c7f5fb3e7b..c573a58f80ab 100644 >>>> --- a/tools/testing/selftests/mm/split_huge_page_test.c >>>> +++ b/tools/testing/selftests/mm/split_huge_page_test.c >>>> @@ -300,7 +300,7 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd, >>>> char **addr) >>>> { >>>> size_t i; >>>> - int __attribute__((unused)) dummy = 0; >>>> + volatile int __attribute__((unused)) dummy = 0; >>>> srand(time(NULL)); >>>> >>>> base-commit: d97496ca23a2d4ee80b7302849404859d9058bcd >>> >>> The rick we do in some other tests is: >>> >>> char *tmp; >>> >>> tmp = *whatever; >>> asm volatile("" : "+r" (tmp)); >> >> char tmp; of course. See cow.c as an example. > Thanks David! I remember also seeing this when I grepped for volatile in > the selftests directory. > > Willy gave the idea of making it as a global variable [1]. But your > trick also works :) > > diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c > index d3c7f5fb3e7b..9c957703c1f7 100644 > --- a/tools/testing/selftests/mm/split_huge_page_test.c > +++ b/tools/testing/selftests/mm/split_huge_page_test.c > @@ -341,6 +341,7 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd, > > for (size_t i = 0; i < fd_size; i++) > dummy += *(*addr + i); > + asm volatile("" : "+r" (dummy)); > > if (!check_huge_file(*addr, fd_size / pmd_pagesize, pmd_pagesize)) { > ksft_print_msg("No large pagecache folio generated, please provide a filesystem supporting large folio\n"); > > I am fine with either solutions. But using the trick asm volatile is more > cleaner than making it a global variable IMO and makes it more uniform > across the other mm tests. You can then even the "__attribute__((unused))", because the compile must assume that it is used inside the asm statement. -- Cheers, David / dhildenb