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dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1715765822; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=taztA4X9SYAad6MljQhp5byUR0uDlX1bSOG8xe6+6QA=; b=l5+wd9t9TnfFfbm+Pf++guMWw0G0cBa72oU71RfV1bVasLr4Fife5US5G3YIr7pHXNb6ID TLNawWzDKNrxHxgwtjg7fRHCByqBZ116TrmLxTVcAoWXaso5HjfrHO43VyzwM3ehEAuiyv 1NQ6kfVs9lHiS3N3c9Yn8PSLmIQIvVw= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A2FDD1474; Wed, 15 May 2024 02:37:26 -0700 (PDT) Received: from e116581.blr.arm.com (e116581.arm.com [10.162.42.15]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id B2AD63F7A6; Wed, 15 May 2024 02:36:58 -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 2/2] selftests/mm: compaction_test: Fix trivial test success and reduce probability of OOM-killer invocation Date: Wed, 15 May 2024 15:06:33 +0530 Message-Id: <20240515093633.54814-3-dev.jain@arm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240515093633.54814-1-dev.jain@arm.com> References: <20240515093633.54814-1-dev.jain@arm.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: BB8D4100010 X-Rspam-User: X-Rspamd-Server: rspam12 X-Stat-Signature: 7ap6jpeq9wnxwaezi7oowzywx84wep7f X-HE-Tag: 1715765822-851875 X-HE-Meta: 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 tksMOJHT bDnCwIXWsAxTDf4o+LCOTrUQ+9EION3RSkp+mCPujGOB5llQ6dXKfY6skD0jWAzpwHxj37VM/6ZhOYLmcAE2xAOmUly+6DzGNIVHyiQAnjoL6rYCRg5puryzS6x7GUmJK7kvABDssK7UY/BzG1tBT7zNy6jovw6y2rwW8FKnDqQ8xA6/DufP1jtC3SsUPY8jsRdDARxQaRck8aYKzcjHles/NAl/wFX8VnnpHGA/4P6Q2cDrCsY/+3ewqbNfgZyTLZ6n0kkGoJv8bNyI= 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 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 | 72 ++++++++++++++------ 1 file changed, 50 insertions(+), 22 deletions(-) diff --git a/tools/testing/selftests/mm/compaction_test.c b/tools/testing/selftests/mm/compaction_test.c index c5be395f8363..2ae059989771 100644 --- a/tools/testing/selftests/mm/compaction_test.c +++ b/tools/testing/selftests/mm/compaction_test.c @@ -82,12 +82,15 @@ int prereq(void) return -1; } -int check_compaction(unsigned long mem_free, unsigned int hugepage_size) +int check_compaction(unsigned long mem_free, unsigned int hugepage_size, + int initial_nr_hugepages) { int fd, ret = -1; int compaction_index = 0; - char initial_nr_hugepages[10] = {0}; char nr_hugepages[10] = {0}; + char init_nr_hugepages[10] = {0}; + + sprintf(init_nr_hugepages, "%d", initial_nr_hugepages); /* We want to test with 80% of available memory. Else, OOM killer comes in to play */ @@ -101,23 +104,6 @@ int check_compaction(unsigned long mem_free, unsigned int 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))) { @@ -140,8 +126,8 @@ int check_compaction(unsigned long mem_free, unsigned int 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; @@ -165,6 +151,42 @@ int check_compaction(unsigned long mem_free, unsigned int hugepage_size) return ret; } +int set_zero_hugepages(int *initial_nr_hugepages) +{ + int fd, ret = -1; + char nr_hugepages[10] = {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 = atoi(nr_hugepages); + ret = 0; + + close_fd: + close(fd); + + out: + return ret; +} int main(int argc, char **argv) { @@ -175,6 +197,7 @@ int main(int argc, char **argv) unsigned long mem_free = 0; unsigned long hugepage_size = 0; long mem_fragmentable_MB = 0; + int initial_nr_hugepages; ksft_print_header(); @@ -183,6 +206,10 @@ 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)) + return ksft_exit_fail(); + lim.rlim_cur = RLIM_INFINITY; lim.rlim_max = RLIM_INFINITY; if (setrlimit(RLIMIT_MEMLOCK, &lim)) @@ -226,7 +253,8 @@ 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) return ksft_exit_pass(); return ksft_exit_fail();