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[2003:d8:2f27:6d00:7b96:afc9:83d0:5bd]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e7607cd0a7sm25851981f8f.39.2025.09.17.06.19.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 Sep 2025 06:19:26 -0700 (PDT) Message-ID: Date: Wed, 17 Sep 2025 15:19:24 +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 v2 3/3] selftests/mm: Added fork test to verify global ksm_zero_pages counter behavior To: Donet Tom , Andrew Morton Cc: Ritesh Harjani , Xu Xin , Chengming Zhou , Wei Yang , Aboorva Devarajan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Giorgi Tchankvetadze References: <5910cb6bfc7c43b169b679a0108667a56d7ebdb8.1757946863.git.donettom@linux.ibm.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <5910cb6bfc7c43b169b679a0108667a56d7ebdb8.1757946863.git.donettom@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 15.09.25 17:03, Donet Tom wrote: > Added a selftest to verify the behavior of the global KSM zero-page > counter during fork. When a process forks, the per-process zero-page > counter is inherited by the child, and the global counter should be > updated with this inherited value. This test ensures that the global > counter is correctly updated after fork. > > Signed-off-by: Donet Tom > --- > .../selftests/mm/ksm_functional_tests.c | 74 ++++++++++++++++++- > 1 file changed, 73 insertions(+), 1 deletion(-) > > diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c > index 645cefba2126..f23597ac8066 100644 > --- a/tools/testing/selftests/mm/ksm_functional_tests.c > +++ b/tools/testing/selftests/mm/ksm_functional_tests.c > @@ -602,6 +602,77 @@ static void test_prot_none(void) > munmap(map, size); > } > > +long ksm_get_global_ksm_zero_pages(void) > +{ > + int global_ksm_zero_pages_fd; > + char buf[10]; > + ssize_t ret; > + > + global_ksm_zero_pages_fd = open("/sys/kernel/mm/ksm/ksm_zero_pages", > + O_RDONLY); > + if (global_ksm_zero_pages_fd < 0) > + return -errno; > + > + ret = pread(global_ksm_zero_pages_fd, buf, sizeof(buf) - 1, 0); > + close(global_ksm_zero_pages_fd); > + if (ret <= 0) > + return -errno; > + buf[ret] = 0; > + > + return strtol(buf, NULL, 10); > +} > + > +static void test_fork_global_ksm_zero_pages_count(void) > +{ > + const unsigned int size = 2 * MiB; > + char *map; > + pid_t child_pid; > + int status; > + long g_zpages_before = 0, g_zpages_after = 0; > + > + ksft_print_msg("[RUN] %s\n", __func__); > + > + /* Unmerge all pages before test */ > + if (ksm_stop() < 0) { > + ksft_test_result_fail("KSM unmerging failed\n"); > + return; > + } > + /* Get the global zero page count before test */ That only works when "use_zero_pages" is enabled, no? > + g_zpages_before = ksm_get_global_ksm_zero_pages(); > + /* Let KSM deduplicate zero pages. */ > + map = mmap_and_merge_range(0x00, size, PROT_READ | PROT_WRITE, KSM_MERGE_MADVISE); > + if (map == MAP_FAILED) > + return; > + > + child_pid = fork(); > + if (!child_pid) { > + exit(ksm_stop()); > + } else if (child_pid < 0) { > + ksft_test_result_fail("fork() failed\n"); > + return; Cleanup missing as for patch #2. > + } > + if (waitpid(child_pid, &status, 0) < 0) { > + ksft_test_result_fail("waitpid() failed\n"); > + return; > + } > + status = WEXITSTATUS(status); > + if (status < 0) { > + ksft_test_result_fail("KSM unmerging failed in child\n"); > + return; > + } > + > + /* Verify global zero-page count remains unchanged */ > + g_zpages_after = ksm_get_global_ksm_zero_pages(); > + if (g_zpages_before != g_zpages_after) { > + ksft_test_result_fail("Incorrect global ksm zero page count after fork\n"); > + return; > + } > + > + ksft_test_result_pass("Global ksm zero page count is correct after fork\n"); > + ksm_stop(); > What stops KSM from merging pages in other processes by accident concurrently and giving false failures? Likely you would want to stop ksm before the fork. -- Cheers David / dhildenb