linux-kernel - [PATCH v2 7/9] selftests/mm: Don't fail uffd-stress if too many CPUs

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Message-ID: <20250221-mm-selftests-v2-7-28c4d66383c5@google.com>
Date: Fri, 21 Feb 2025 18:25:46 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Shuah Khan <shuah@...nel.org>
Cc: Dev Jain <dev.jain@....com>, linux-mm@...ck.org, linux-kselftest@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Brendan Jackman <jackmanb@...gle.com>, 
	Mateusz Guzik <mjguzik@...il.com>
Subject: [PATCH v2 7/9] selftests/mm: Don't fail uffd-stress if too many CPUs

This calculation divides a fixed parameter by an environment-dependent
parameter i.e. the number of CPUs.

The simple way to avoid machine-specific failures here is to just put a
cap on the max value of the latter.

Suggested-by: Mateusz Guzik <mjguzik@...il.com>
Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
---
 tools/testing/selftests/mm/uffd-stress.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/uffd-stress.c b/tools/testing/selftests/mm/uffd-stress.c
index be0c93f24fccd618f52d54ff36d9a5540f420e46..cfadac801ed43e8b6dc331b343b6dc4030048f9b 100644
--- a/tools/testing/selftests/mm/uffd-stress.c
+++ b/tools/testing/selftests/mm/uffd-stress.c
@@ -434,6 +434,7 @@ static void sigalrm(int sig)
 
 int main(int argc, char **argv)
 {
+	unsigned long nr_cpus;
 	size_t bytes;
 
 	if (argc < 4)
@@ -452,7 +453,15 @@ int main(int argc, char **argv)
 		return KSFT_SKIP;
 	}
 
-	nr_threads = sysconf(_SC_NPROCESSORS_ONLN);
+	nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
+	if (nr_cpus > 32) {
+		/* Don't let calculation below go to zero. */
+		ksft_print_msg("_SC_NPROCESSORS_ONLN (%lu) too large, capping nr_threads to 32\n",
+			       nr_cpus);
+		nr_threads = 32;
+	} else {
+		nr_cpus = nr_threads;
+	}
 
 	nr_pages_per_cpu = bytes / page_size / nr_threads;
 	if (!nr_pages_per_cpu) {

-- 
2.48.1.601.g30ceb7b040-goog