linux-kernel - [PATCH] lib/test_vmalloc.c: Minor fixes to test

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Message-ID: <20251201181848.1216197-1-audra@redhat.com>
Date: Mon,  1 Dec 2025 13:18:48 -0500
From: Audra Mitchell <audra@...hat.com>
To: shuah@...nel.org
Cc: linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	mhocko@...e.com,
	surenb@...gle.com,
	rppt@...nel.org,
	vbabka@...e.cz,
	Liam.Howlett@...cle.com,
	lorenzo.stoakes@...cle.com,
	david@...nel.org,
	urezki@...il.com,
	raquini@...hat.com,
	akpm@...ux-foundation.org
Subject: [PATCH] lib/test_vmalloc.c: Minor fixes to test_vmalloc.c

If PAGE_SIZE is larger than 4k and if you have a system with a
large number of CPUs, this test can require a very large amount
of memory leading to oom-killer firing. Given the type of allocation,
the kernel won't have anything to kill, causing the system to
stall. Add a parameter to the test_vmalloc driver to represent the
number of times a percpu object will be allocated. Calculate this
in test_vmalloc.sh to be 90% of available memory or the current
default of 35000, whichever is smaller.

Signed-off-by: Audra Mitchell <audra@...hat.com>
---
 lib/test_vmalloc.c                         | 11 +++++---
 tools/testing/selftests/mm/test_vmalloc.sh | 31 +++++++++++++++++++---
 2 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/lib/test_vmalloc.c b/lib/test_vmalloc.c
index 2815658ccc37..67e53cd6b619 100644
--- a/lib/test_vmalloc.c
+++ b/lib/test_vmalloc.c
@@ -57,6 +57,9 @@ __param(int, run_test_mask, 7,
 		/* Add a new test case description here. */
 );
 
+__param(int, nr_pcpu_objects, 35000,
+	"Number of pcpu objects to allocate for pcpu_alloc_test");
+
 /*
  * This is for synchronization of setup phase.
  */
@@ -292,24 +295,24 @@ pcpu_alloc_test(void)
 	size_t size, align;
 	int i;
 
-	pcpu = vmalloc(sizeof(void __percpu *) * 35000);
+	pcpu = vmalloc(sizeof(void __percpu *) * nr_pcpu_objects);
 	if (!pcpu)
 		return -1;
 
-	for (i = 0; i < 35000; i++) {
+	for (i = 0; i < nr_pcpu_objects; i++) {
 		size = get_random_u32_inclusive(1, PAGE_SIZE / 4);
 
 		/*
 		 * Maximum PAGE_SIZE
 		 */
-		align = 1 << get_random_u32_inclusive(1, 11);
+		align = 1 << get_random_u32_inclusive(1, PAGE_SHIFT - 1);
 
 		pcpu[i] = __alloc_percpu(size, align);
 		if (!pcpu[i])
 			rv = -1;
 	}
 
-	for (i = 0; i < 35000; i++)
+	for (i = 0; i < nr_pcpu_objects; i++)
 		free_percpu(pcpu[i]);
 
 	vfree(pcpu);
diff --git a/tools/testing/selftests/mm/test_vmalloc.sh b/tools/testing/selftests/mm/test_vmalloc.sh
index d39096723fca..b23d705bf570 100755
--- a/tools/testing/selftests/mm/test_vmalloc.sh
+++ b/tools/testing/selftests/mm/test_vmalloc.sh
@@ -13,6 +13,9 @@ TEST_NAME="vmalloc"
 DRIVER="test_${TEST_NAME}"
 NUM_CPUS=`grep -c ^processor /proc/cpuinfo`
 
+# Default number of times we allocate percpu objects:
+NR_PCPU_OBJECTS=35000
+
 # 1 if fails
 exitcode=1
 
@@ -27,6 +30,8 @@ PERF_PARAM="sequential_test_order=1 test_repeat_count=3"
 SMOKE_PARAM="test_loop_count=10000 test_repeat_count=10"
 STRESS_PARAM="nr_threads=$NUM_CPUS test_repeat_count=20"
 
+PCPU_OBJ_PARAM="nr_pcpu_objects=$NR_PCPU_OBJECTS"
+
 check_test_requirements()
 {
 	uid=$(id -u)
@@ -47,12 +52,30 @@ check_test_requirements()
 	fi
 }
 
+check_memory_requirement()
+{
+	# The pcpu_alloc_test allocates nr_pcpu_objects per cpu. If the
+	# PAGE_SIZE is on the larger side it is easier to set a value
+	# that can cause oom events during testing. Since we are
+	# testing the functionality of vmalloc and not the oom-killer,
+	# calculate what is 90% of available memory and divide it by
+	# the number of online CPUs.
+	pages=$(($(getconf _AVPHYS_PAGES) * 90 / 100 / $NUM_CPUS))
+
+	if (($pages < $NR_PCPU_OBJECTS)); then
+		echo "Updated nr_pcpu_objects to 90% of available memory."
+		echo "nr_pcpu_objects is now set to: $pages."
+		PCPU_OBJ_PARAM="nr_pcpu_objects=$pages"
+	fi
+}
+
 run_performance_check()
 {
 	echo "Run performance tests to evaluate how fast vmalloc allocation is."
 	echo "It runs all test cases on one single CPU with sequential order."
 
-	modprobe $DRIVER $PERF_PARAM > /dev/null 2>&1
+	check_memory_requirement
+	modprobe $DRIVER $PERF_PARAM $PCPU_OBJ_PARAM > /dev/null 2>&1
 	echo "Done."
 	echo "Check the kernel message buffer to see the summary."
 }
@@ -63,7 +86,8 @@ run_stability_check()
 	echo "available test cases are run by NUM_CPUS workers simultaneously."
 	echo "It will take time, so be patient."
 
-	modprobe $DRIVER $STRESS_PARAM > /dev/null 2>&1
+	check_memory_requirement
+	modprobe $DRIVER $STRESS_PARAM $PCPU_OBJ_PARAM > /dev/null 2>&1
 	echo "Done."
 	echo "Check the kernel ring buffer to see the summary."
 }
@@ -74,7 +98,8 @@ run_smoke_check()
 	echo "Please check $0 output how it can be used"
 	echo "for deep performance analysis as well as stress testing."
 
-	modprobe $DRIVER $SMOKE_PARAM > /dev/null 2>&1
+	check_memory_requirement
+	modprobe $DRIVER $SMOKE_PARAM $PCPU_OBJ_PARAM > /dev/null 2>&1
 	echo "Done."
 	echo "Check the kernel ring buffer to see the summary."
 }
-- 
2.51.0