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Tue, 21 May 2024 00:44:27 -0700 (PDT) From: Dev Jain To: akpm@linux-foundation.org, shuah@kernel.org Cc: linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Anshuman.Khandual@arm.com, sjayaram@akamai.com, Dev Jain , stable@vger.kernel.org Subject: [PATCH v2 3/3] selftests/mm: compaction_test: Fix bogus test success and reduce probability of OOM-killer invocation Date: Tue, 21 May 2024 13:13:58 +0530 Message-Id: <20240521074358.675031-4-dev.jain@arm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240521074358.675031-1-dev.jain@arm.com> References: <20240521074358.675031-1-dev.jain@arm.com> MIME-Version: 1.0 X-Stat-Signature: 8kzbx8cpj9nygdy543xsxx6jqukcoean X-Rspamd-Queue-Id: CD3C84000A X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1716277471-826131 X-HE-Meta: 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 pQcHbu6G qtmH3ewWlM5uR6E+eXoZfL8J4wBJAKd9mbW/RZddyhkHVVCZ1tJi/tILe+KlklO1FgMdW9IqAG8JEqgi8GvD77yYE2QSGFBhmoI3NXJsu9TjENTuHhmLXnFTdYKL63RbewR8eOA5AYHVZG4z4yI0MYFfD9KSqavXZssg2WPbkeCLXvfJlPzGMNqgFK20JBNvn+7lqxMjG1/NKFJHd/wybweCIjcaO1OsdA3hHaOMcFn/kySKNPtn21tHngeBotAKahPivUrsqGKI1EY8= 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: Reset nr_hugepages to zero before the start of the test. If a non-zero number of hugepages is already set before the start of the test, the following problems arise: - The probability of the test getting OOM-killed increases. Proof: The test wants to run on 80% of available memory to prevent OOM-killing (see original code comments). Let the value of mem_free at the start of the test, when nr_hugepages = 0, be x. In the other case, when nr_hugepages > 0, let the memory consumed by hugepages be y. In the former case, the test operates on 0.8 * x of memory. In the latter, the test operates on 0.8 * (x - y) of memory, with y already filled, hence, memory consumed is y + 0.8 * (x - y) = 0.8 * x + 0.2 * y > 0.8 * x. Q.E.D - The probability of a bogus test success increases. Proof: Let the memory consumed by hugepages be greater than 25% of x, with x and y defined as above. The definition of compaction_index is c_index = (x - y)/z where z is the memory consumed by hugepages after trying to increase them again. In check_compaction(), we set the number of hugepages to zero, and then increase them back; the probability that they will be set back to consume at least y amount of memory again is very high (since there is not much delay between the two attempts of changing nr_hugepages). Hence, z >= y > (x/4) (by the 25% assumption). Therefore, c_index = (x - y)/z <= (x - y)/y = x/y - 1 < 4 - 1 = 3 hence, c_index can always be forced to be less than 3, thereby the test succeeding always. Q.E.D Changes in v2: - Handle unsigned long number of hugepages v1: - https://lore.kernel.org/all/20240515093633.54814-3-dev.jain@arm.com/ NOTE: This patch depends on the previous one. Fixes: bd67d5c15cc1 ("Test compaction of mlocked memory") Cc: stable@vger.kernel.org Signed-off-by: Dev Jain --- tools/testing/selftests/mm/compaction_test.c | 71 ++++++++++++++------ 1 file changed, 49 insertions(+), 22 deletions(-) diff --git a/tools/testing/selftests/mm/compaction_test.c b/tools/testing/selftests/mm/compaction_test.c index 5e9bd1da9370..e140558e6f53 100644 --- a/tools/testing/selftests/mm/compaction_test.c +++ b/tools/testing/selftests/mm/compaction_test.c @@ -82,13 +82,16 @@ int prereq(void) return -1; } -int check_compaction(unsigned long mem_free, unsigned long hugepage_size) +int check_compaction(unsigned long mem_free, unsigned long hugepage_size, + unsigned long initial_nr_hugepages) { unsigned long nr_hugepages_ul; int fd, ret = -1; int compaction_index = 0; - char initial_nr_hugepages[20] = {0}; char nr_hugepages[20] = {0}; + char init_nr_hugepages[20] = {0}; + + sprintf(init_nr_hugepages, "%lu", initial_nr_hugepages); /* We want to test with 80% of available memory. Else, OOM killer comes in to play */ @@ -102,23 +105,6 @@ int check_compaction(unsigned long mem_free, unsigned long hugepage_size) goto out; } - if (read(fd, initial_nr_hugepages, sizeof(initial_nr_hugepages)) <= 0) { - ksft_print_msg("Failed to read from /proc/sys/vm/nr_hugepages: %s\n", - strerror(errno)); - goto close_fd; - } - - lseek(fd, 0, SEEK_SET); - - /* Start with the initial condition of 0 huge pages*/ - if (write(fd, "0", sizeof(char)) != sizeof(char)) { - ksft_print_msg("Failed to write 0 to /proc/sys/vm/nr_hugepages: %s\n", - strerror(errno)); - goto close_fd; - } - - lseek(fd, 0, SEEK_SET); - /* Request a large number of huge pages. The Kernel will allocate as much as it can */ if (write(fd, "100000", (6*sizeof(char))) != (6*sizeof(char))) { @@ -146,8 +132,8 @@ int check_compaction(unsigned long mem_free, unsigned long hugepage_size) lseek(fd, 0, SEEK_SET); - if (write(fd, initial_nr_hugepages, strlen(initial_nr_hugepages)) - != strlen(initial_nr_hugepages)) { + if (write(fd, init_nr_hugepages, strlen(init_nr_hugepages)) + != strlen(init_nr_hugepages)) { ksft_print_msg("Failed to write value to /proc/sys/vm/nr_hugepages: %s\n", strerror(errno)); goto close_fd; @@ -171,6 +157,41 @@ int check_compaction(unsigned long mem_free, unsigned long hugepage_size) return ret; } +int set_zero_hugepages(unsigned long *initial_nr_hugepages) +{ + int fd, ret = -1; + char nr_hugepages[20] = {0}; + + fd = open("/proc/sys/vm/nr_hugepages", O_RDWR | O_NONBLOCK); + if (fd < 0) { + ksft_print_msg("Failed to open /proc/sys/vm/nr_hugepages: %s\n", + strerror(errno)); + goto out; + } + if (read(fd, nr_hugepages, sizeof(nr_hugepages)) <= 0) { + ksft_print_msg("Failed to read from /proc/sys/vm/nr_hugepages: %s\n", + strerror(errno)); + goto close_fd; + } + + lseek(fd, 0, SEEK_SET); + + /* Start with the initial condition of 0 huge pages */ + if (write(fd, "0", sizeof(char)) != sizeof(char)) { + ksft_print_msg("Failed to write 0 to /proc/sys/vm/nr_hugepages: %s\n", + strerror(errno)); + goto close_fd; + } + + *initial_nr_hugepages = strtoul(nr_hugepages, NULL, 10); + ret = 0; + + close_fd: + close(fd); + + out: + return ret; +} int main(int argc, char **argv) { @@ -181,6 +202,7 @@ int main(int argc, char **argv) unsigned long mem_free = 0; unsigned long hugepage_size = 0; long mem_fragmentable_MB = 0; + unsigned long initial_nr_hugepages; ksft_print_header(); @@ -189,6 +211,10 @@ int main(int argc, char **argv) ksft_set_plan(1); + /* Start the test without hugepages reducing mem_free */ + if (set_zero_hugepages(&initial_nr_hugepages)) + ksft_exit_fail(); + lim.rlim_cur = RLIM_INFINITY; lim.rlim_max = RLIM_INFINITY; if (setrlimit(RLIMIT_MEMLOCK, &lim)) @@ -232,7 +258,8 @@ int main(int argc, char **argv) entry = entry->next; } - if (check_compaction(mem_free, hugepage_size) == 0) + if (check_compaction(mem_free, hugepage_size, + initial_nr_hugepages) == 0) ksft_exit_pass(); ksft_exit_fail();