[PATCH v4 5/7] selftests/cgroup: replace hardcoded page size values in test_zswap

[Li Wang <liwang@redhat.com>]

test_zswap uses hardcoded values of 4095 and 4096 throughout as page
stride and page size, which are only correct on systems with a 4K page
size. On architectures with larger pages (e.g., 64K on arm64 or ppc64),
these constants cause memory to be touched at sub-page granularity,
leading to inefficient access patterns and incorrect page count
calculations, which can cause test failures.

Replace all hardcoded 4095 and 4096 values with a global pagesize
variable initialized from sysconf(_SC_PAGESIZE) at startup, and remove
the redundant local sysconf() calls scattered across individual
functions. No functional change on 4K page size systems.

Signed-off-by: Li Wang <liwang@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>
---
 tools/testing/selftests/cgroup/test_zswap.c | 22 +++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index 4982e8c4759c..407cfb6ae34d 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -13,6 +13,8 @@
 #include "kselftest.h"
 #include "cgroup_util.h"
 
+static size_t pagesize;
+
 static int read_int(const char *path, size_t *value)
 {
 	FILE *file;
@@ -68,11 +70,11 @@ static int allocate_and_read_bytes(const char *cgroup, void *arg)
 
 	if (!mem)
 		return -1;
-	for (int i = 0; i < size; i += 4095)
+	for (int i = 0; i < size; i += pagesize)
 		mem[i] = 'a';
 
 	/* Go through the allocated memory to (z)swap in and out pages */
-	for (int i = 0; i < size; i += 4095) {
+	for (int i = 0; i < size; i += pagesize) {
 		if (mem[i] != 'a')
 			ret = -1;
 	}
@@ -88,7 +90,7 @@ static int allocate_bytes(const char *cgroup, void *arg)
 
 	if (!mem)
 		return -1;
-	for (int i = 0; i < size; i += 4095)
+	for (int i = 0; i < size; i += pagesize)
 		mem[i] = 'a';
 	free(mem);
 	return 0;
@@ -267,7 +269,6 @@ static int test_zswapin(const char *root)
  */
 static int attempt_writeback(const char *cgroup, void *arg)
 {
-	long pagesize = sysconf(_SC_PAGESIZE);
 	size_t memsize = MB(4);
 	char buf[pagesize];
 	long zswap_usage;
@@ -436,7 +437,7 @@ static int test_no_invasive_cgroup_shrink(const char *root)
 	if (cg_enter_current(control_group))
 		goto out;
 	control_allocation = malloc(control_allocation_size);
-	for (int i = 0; i < control_allocation_size; i += 4095)
+	for (int i = 0; i < control_allocation_size; i += pagesize)
 		control_allocation[i] = 'a';
 	if (cg_read_key_long(control_group, "memory.stat", "zswapped") < 1)
 		goto out;
@@ -476,7 +477,7 @@ static int no_kmem_bypass_child(const char *cgroup, void *arg)
 		values->child_allocated = true;
 		return -1;
 	}
-	for (long i = 0; i < values->target_alloc_bytes; i += 4095)
+	for (long i = 0; i < values->target_alloc_bytes; i += pagesize)
 		((char *)allocation)[i] = 'a';
 	values->child_allocated = true;
 	pause();
@@ -524,7 +525,7 @@ static int test_no_kmem_bypass(const char *root)
 	min_free_kb_low = sys_info.totalram / 500000;
 	values->target_alloc_bytes = (sys_info.totalram - min_free_kb_high * 1000) +
 		sys_info.totalram * 5 / 100;
-	stored_pages_threshold = sys_info.totalram / 5 / 4096;
+	stored_pages_threshold = sys_info.totalram / 5 / pagesize;
 	trigger_allocation_size = sys_info.totalram / 20;
 
 	/* Set up test memcg */
@@ -551,7 +552,7 @@ static int test_no_kmem_bypass(const char *root)
 
 		if (!trigger_allocation)
 			break;
-		for (int i = 0; i < trigger_allocation_size; i += 4095)
+		for (int i = 0; i < trigger_allocation_size; i += pagesize)
 			trigger_allocation[i] = 'b';
 		usleep(100000);
 		free(trigger_allocation);
@@ -562,8 +563,8 @@ static int test_no_kmem_bypass(const char *root)
 		/* If memory was pushed to zswap, verify it belongs to memcg */
 		if (stored_pages > stored_pages_threshold) {
 			int zswapped = cg_read_key_long(test_group, "memory.stat", "zswapped ");
-			int delta = stored_pages * 4096 - zswapped;
-			int result_ok = delta < stored_pages * 4096 / 4;
+			int delta = stored_pages * pagesize - zswapped;
+			int result_ok = delta < stored_pages * pagesize / 4;
 
 			ret = result_ok ? KSFT_PASS : KSFT_FAIL;
 			break;
@@ -616,6 +617,7 @@ int main(int argc, char **argv)
 	char root[PATH_MAX];
 	int i;
 
+	pagesize = sysconf(_SC_PAGESIZE);
 	ksft_print_header();
 	ksft_set_plan(ARRAY_SIZE(tests));
 	if (cg_find_unified_root(root, sizeof(root), NULL))
-- 
2.53.0