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[2003:cb:c70d:3a00:d73c:6a8:ca9f:1df7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a1c89e2dfsm53584503f8f.74.2025.01.08.05.30.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Jan 2025 05:30:25 -0800 (PST) Message-ID: <63481999-0665-4f40-a1bd-377a6ae69f90@redhat.com> Date: Wed, 8 Jan 2025 14:30:23 +0100 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/3] selftests/mm: virtual_address_range: Dump to /dev/null To: Dev Jain , =?UTF-8?Q?Thomas_Wei=C3=9Fschuh?= , Andrew Morton , Shuah Khan , Thomas Gleixner Cc: linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Ryan Roberts References: <20250107-virtual_address_range-tests-v1-0-3834a2fb47fe@linutronix.de> <20250107-virtual_address_range-tests-v1-3-3834a2fb47fe@linutronix.de> <2c5ab3af-2e58-449a-94f2-5cbcaa8b66f2@arm.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: <2c5ab3af-2e58-449a-94f2-5cbcaa8b66f2@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 08.01.25 07:09, Dev Jain wrote: > > On 07/01/25 8:44 pm, Thomas Weißschuh wrote: >> During the execution of validate_complete_va_space() a lot of memory is >> on the VM subsystem. When running on a low memory subsystem an OOM may >> be triggered, when writing to the dump file as the filesystem may also >> require memory. >> >> On my test system with 1100MiB physical memory: >> >> Tasks state (memory values in pages): >> [ pid ] uid tgid total_vm rss rss_anon rss_file rss_shmem pgtables_bytes swapents oom_score_adj name >> [ 57] 0 57 34359215953 695 256 0 439 1064390656 0 0 virtual_address >> >> Out of memory: Killed process 57 (virtual_address) total-vm:137436863812kB, anon-rss:1024kB, file-rss:0kB, shmem-rss:1756kB, UID:0 pgtables:1039444kB oom_score_adj:0 >> >> fault_in_iov_iter_readable+0x4a/0xd0 >> generic_perform_write+0x9c/0x280 >> shmem_file_write_iter+0x86/0x90 >> vfs_write+0x29c/0x480 >> ksys_write+0x6c/0xe0 >> do_syscall_64+0x9e/0x1a0 >> entry_SYSCALL_64_after_hwframe+0x77/0x7f >> >> Write the dumped data into /dev/null instead which does not require >> additional memory during write(), making the code simpler as a >> side-effect. >> >> Signed-off-by: Thomas Weißschuh >> --- >> tools/testing/selftests/mm/virtual_address_range.c | 6 ++---- >> 1 file changed, 2 insertions(+), 4 deletions(-) >> >> diff --git a/tools/testing/selftests/mm/virtual_address_range.c b/tools/testing/selftests/mm/virtual_address_range.c >> index 484f82c7b7c871f82a7d9ec6d6c649f2ab1eb0cd..4042fd878acd702d23da2c3293292de33bd48143 100644 >> --- a/tools/testing/selftests/mm/virtual_address_range.c >> +++ b/tools/testing/selftests/mm/virtual_address_range.c >> @@ -103,10 +103,9 @@ static int validate_complete_va_space(void) >> FILE *file; >> int fd; >> >> - fd = open("va_dump", O_CREAT | O_WRONLY, 0600); >> - unlink("va_dump"); >> + fd = open("/dev/null", O_WRONLY); >> if (fd < 0) { >> - ksft_test_result_skip("cannot create or open dump file\n"); >> + ksft_test_result_skip("cannot create or open /dev/null\n"); >> ksft_finished(); >> } >> >> @@ -152,7 +151,6 @@ static int validate_complete_va_space(void) >> while (start_addr + hop < end_addr) { >> if (write(fd, (void *)(start_addr + hop), 1) != 1) >> return 1; >> - lseek(fd, 0, SEEK_SET); >> >> hop += MAP_CHUNK_SIZE; >> } >> > > The reason I had not used /dev/null was that write() was succeeding to /dev/null > even from an address not in my VA space. I was puzzled about this behaviour of > /dev/null and I chose to ignore it and just use a real file. > > To test this behaviour, run the following program: > > #include > #include > #include > #include > #include > intmain() > { > intfd; > fd = open("va_dump", O_CREAT| O_WRONLY, 0600); > unlink("va_dump"); > // fd = open("/dev/null", O_WRONLY); > intret = munmap((void*)(1UL<< 30), 100); > if(!ret) > printf("munmap succeeded\n"); > intres = write(fd, (void*)(1UL<< 30), 1); > if(res == 1) > printf("write succeeded\n"); > return0; > } > The write will fail as expected, but if you comment out the va_dump > lines and use /dev/null, the write will succeed. What exactly do we want to achieve with the write? Verify that the output of /proc/self/map is reasonable and we can actually resolve a fault / map a page? Why not access the memory directly+signal handler or using /proc/self/mem, so you can avoid the temp file completely? -- Cheers, David / dhildenb