>> + if (write(ksm_use_zero_pages_fd, "1", 1) != 1) {
>> + ksft_test_result_skip("write \"/sys/kernel/mm/ksm/use_zero_pages\" failed\n");
>> + return;
>> + }
>
>I realize that this test will fail if there is any other process in the system that has KSM
>Enabled with a suitable page filled with zeroes ... maybe instead of checking the global
>KSM zeropages, check the per-mm ones instead? That should be better
Emmm, yes. It makes sense. I'll do it per-mm in next-version.
>You could do something like the following on top (I recall you had some kind of COW
>tests previously, this should be a simplified version of it):
>
Ok. Thank you.
>diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
>index ea060c683c80..160675a4e3d2 100644
>--- a/tools/testing/selftests/mm/ksm_functional_tests.c
>+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
>@@ -182,6 +182,7 @@ static void test_unmerge(void)
> static void test_unmerge_zero_pages(void)
> {
> const unsigned int size = 2 * MiB;
>+ unsigned int offs;
> char *map;
> unsigned long pages_expected;
>
>@@ -225,8 +226,18 @@ static void test_unmerge_zero_pages(void)
> goto unmap;
> }
>
>+ /* Trigger unmerging of the other half by writing to the pages. */
>+ for (offs = size / 2; offs < size; offs += pagesize)
>+ *((unsigned int *)&map[offs]) = offs;
>+
>+ /* We should have no zeropages remaining. */
>+ if (get_ksm_zero_pages()) {
>+ ksft_test_result_fail("'ksm_zero_pages' updated after write fault\n");
>+ goto unmap;
>+ }
>+
> /* Check if ksm zero pages are really unmerged */
>- ksft_test_result(!range_maps_duplicates(map, size / 2),
>+ ksft_test_result(!range_maps_duplicates(map, size),
> "KSM zero pages were unmerged\n");
> unmap:
> munmap(map, size);
