[PATCH 4/7] selftests: memcg: Increase error tolerance in accordance with page size

[Waiman Long <longman@redhat.com>]

It was found that some of the tests in test_memcontrol can fail more
readily if system page size is larger than 4k. It is because the actual
memory.current value deviates more from the expected value with larger
page size.  To avoid this failure, the error tolerance is now increased
in accordance to the current system page size value. The page size
scale factor is set to 2 for 64k page and 1 for 16k page.

Changes are made in alloc_pagecache_max_30M(), test_memcg_protection()
and alloc_anon_50M_check_swap() to increase the error tolerance for
memory.current for larger page size. The current set of values are
chosen to ensure that the relevant test_memcontrol tests no longer
have any test failure in a 100 repeated run of test_memcontrol with a
4k/16k/64k page size kernels on an arm64 system.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 .../cgroup/lib/include/cgroup_util.h          |  1 +
 .../selftests/cgroup/test_memcontrol.c        | 23 ++++++++++++++-----
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
index 77f386dab5e8..c25228a78b8b 100644
--- a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
+++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
@@ -6,6 +6,7 @@
 #define PAGE_SIZE 4096
 #endif
 
+#define KB(x) (x << 10)
 #define MB(x) (x << 20)
 
 #define USEC_PER_SEC	1000000L
diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
index 3cc8a432be91..2c3a838536ae 100644
--- a/tools/testing/selftests/cgroup/test_memcontrol.c
+++ b/tools/testing/selftests/cgroup/test_memcontrol.c
@@ -26,6 +26,7 @@
 static bool has_localevents;
 static bool has_recursiveprot;
 static int page_size;
+static int pscale_factor;	/* Page size scale factor */
 
 int get_temp_fd(void)
 {
@@ -571,16 +572,17 @@ static int test_memcg_protection(const char *root, bool min)
 	if (cg_run(parent[2], alloc_anon, (void *)MB(148)))
 		goto cleanup;
 
-	if (!values_close(cg_read_long(parent[1], "memory.current"), MB(50), 3))
+	if (!values_close(cg_read_long(parent[1], "memory.current"), MB(50),
+				       3 + (min ? 0 : 4) * pscale_factor))
 		goto cleanup;
 
 	for (i = 0; i < ARRAY_SIZE(children); i++)
 		c[i] = cg_read_long(children[i], "memory.current");
 
-	if (!values_close(c[0], MB(29), 15))
+	if (!values_close(c[0], MB(29), 15 + 3 * pscale_factor))
 		goto cleanup;
 
-	if (!values_close(c[1], MB(21), 20))
+	if (!values_close(c[1], MB(21), 20 + pscale_factor))
 		goto cleanup;
 
 	if (c[3] != 0)
@@ -596,7 +598,8 @@ static int test_memcg_protection(const char *root, bool min)
 	}
 
 	current = min ? MB(50) : MB(30);
-	if (!values_close(cg_read_long(parent[1], "memory.current"), current, 3))
+	if (!values_close(cg_read_long(parent[1], "memory.current"), current,
+				       9 + (min ? 0 : 6) * pscale_factor))
 		goto cleanup;
 
 	if (!reclaim_until(children[0], MB(10)))
@@ -684,7 +687,7 @@ static int alloc_pagecache_max_30M(const char *cgroup, void *arg)
 		goto cleanup;
 
 	current = cg_read_long(cgroup, "memory.current");
-	if (!values_close(current, MB(30), 5))
+	if (!values_close(current, MB(30), 5 + (pscale_factor ? 2 : 0)))
 		goto cleanup;
 
 	ret = 0;
@@ -1004,7 +1007,7 @@ static int alloc_anon_50M_check_swap(const char *cgroup, void *arg)
 		*ptr = 0;
 
 	mem_current = cg_read_long(cgroup, "memory.current");
-	if (!mem_current || !values_close(mem_current, mem_max, 3))
+	if (!mem_current || !values_close(mem_current, mem_max, 6 + pscale_factor))
 		goto cleanup;
 
 	swap_current = cg_read_long(cgroup, "memory.swap.current");
@@ -1681,6 +1684,14 @@ int main(int argc, char **argv)
 	int i, proc_status;
 
 	page_size = sysconf(_SC_PAGE_SIZE);
+	/*
+	 * It is found that the actual memory.current value can deviate more
+	 * from the expected value with larger page size. So error tolerance
+	 * will have to be increased a bit more for larger page size.
+	 */
+	if (page_size > KB(4))
+		pscale_factor = (page_size >= KB(64)) ? 2 : 1;
+
 	ksft_print_header();
 	ksft_set_plan(ARRAY_SIZE(tests));
 	if (cg_find_unified_root(root, sizeof(root), NULL))
-- 
2.53.0