linux-kernel - [PATCH v4 06/12] selftests/mm: Don't fail uffd-stress if too many CPUs

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Message-ID: <20250311-mm-selftests-v4-6-dec210a658f5@google.com>
Date: Tue, 11 Mar 2025 13:18:17 +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 v4 06/12] 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 4ba5bf13a0108435ce8b53340b9e17ccd47e859e..40af7f67c4074d901be6608e5d64bd0490026dae 100644
--- a/tools/testing/selftests/mm/uffd-stress.c
+++ b/tools/testing/selftests/mm/uffd-stress.c
@@ -435,6 +435,7 @@ static void sigalrm(int sig)
 
 int main(int argc, char **argv)
 {
+	unsigned long nr_cpus;
 	size_t bytes;
 
 	if (argc < 4)
@@ -453,7 +454,15 @@ int main(int argc, char **argv)
 		return KSFT_SKIP;
 	}
 
-	nr_parallel = 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_parallel = 32;
+	} else {
+		nr_parallel = nr_cpus;
+	}
 
 	nr_pages_per_cpu = bytes / page_size / nr_parallel;
 	if (!nr_pages_per_cpu) {

-- 
2.49.0.rc0.332.g42c0ae87b1-goog