[PATCH v2 7/8] selftest/mm: ksm_functional_tests: test in mmap_and_merge_range() if anything got merged

David Hildenbrand
2023-08-01T12:51:04Z

Let's extend mmap_and_merge_range() to test if anything in the current
process was merged. range_maps_duplicates() is too unreliable for that
use case, so instead look at KSM stats.

Trigger a complete unmerge first, to cleanup the stable tree and
stabilize accounting of merged pages.

Note that we're using /proc/self/ksm_merging_pages instead of
/proc/self/ksm_stat, because that one is available in more existing
kernels.

If /proc/self/ksm_merging_pages can't be opened, we can't perform any
checks and simply skip them.

We have to special-case the shared zeropage for now. But the only user
-- test_unmerge_zero_pages() -- performs its own merge checks.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
.../selftests/mm/ksm_functional_tests.c | 47 +++++++++++++++++++
1 file changed, 47 insertions(+)

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index 0de9d33cd565..cb63b600cb4f 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -30,6 +30,7 @@
static int ksm_fd;
static int ksm_full_scans_fd;
static int proc_self_ksm_stat_fd;
+static int proc_self_ksm_merging_pages_fd;
static int ksm_use_zero_pages_fd;
static int pagemap_fd;
static size_t pagesize;
@@ -88,6 +89,22 @@ static long get_my_ksm_zero_pages(void)
return my_ksm_zero_pages;
}

+static long get_my_merging_pages(void)
+{
+ char buf[10];
+ ssize_t ret;
+
+ if (proc_self_ksm_merging_pages_fd < 0)
+ return proc_self_ksm_merging_pages_fd;
+
+ ret = pread(proc_self_ksm_merging_pages_fd, buf, sizeof(buf) - 1, 0);
+ if (ret <= 0)
+ return -errno;
+ buf[ret] = 0;
+
+ return strtol(buf, NULL, 10);
+}
+
static long ksm_get_full_scans(void)
{
char buf[10];
@@ -120,11 +137,29 @@ static int ksm_merge(void)
return 0;
}

+static int ksm_unmerge(void)
+{
+ if (write(ksm_fd, "2", 1) != 1)
+ return -errno;
+ return 0;
+}
+
static char *mmap_and_merge_range(char val, unsigned long size, bool use_prctl)
{
char *map;
int ret;

+ /* Stabilize accounting by disabling KSM completely. */
+ if (ksm_unmerge()) {
+ ksft_test_result_fail("Disabling (unmerging) KSM failed\n");
+ goto unmap;
+ }
+
+ if (get_my_merging_pages() > 0) {
+ ksft_test_result_fail("Still pages merged\n");
+ goto unmap;
+ }
+
map = mmap(NULL, size, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANON, -1, 0);
if (map == MAP_FAILED) {
@@ -160,6 +195,16 @@ static char *mmap_and_merge_range(char val, unsigned long size, bool use_prctl)
ksft_test_result_fail("Running KSM failed\n");
goto unmap;
}
+
+ /*
+ * Check if anything was merged at all. Ignore the zero page that is
+ * accounted differently (depending on kernel support).
+ */
+ if (val && !get_my_merging_pages()) {
+ ksft_test_result_fail("No pages got merged\n");
+ goto unmap;
+ }
+
return map;
unmap:
munmap(map, size);
@@ -473,6 +518,8 @@ int main(int argc, char **argv)
if (pagemap_fd < 0)
ksft_exit_skip("open(\"/proc/self/pagemap\") failed\n");
proc_self_ksm_stat_fd = open("/proc/self/ksm_stat", O_RDONLY);
+ proc_self_ksm_merging_pages_fd = open("/proc/self/ksm_merging_pages",
+ O_RDONLY);
ksm_use_zero_pages_fd = open("/sys/kernel/mm/ksm/use_zero_pages", O_RDWR);

test_unmerge();
--
2.41.0