selftest: add a testcase of ksm zero pages

Add a function test_unmerge_zero_page() to test the functionality on
unsharing and counting ksm-placed zero pages and counting of this patch
series.

test_unmerge_zero_page() actually contains four subjct test objects:
(1) whether the count of ksm zero pages can update correctly after merging;
(2) whether the count of ksm zero pages can update correctly after
    unmerging by madvise(...MADV_UNMERGEABLE);
(3) whether the count of ksm zero pages can update correctly after
	unmerging by triggering write fault.
(4) whether ksm zero pages are really unmerged.

Link: https://lkml.kernel.org/r/20230613030947.186089-1-yang.yang29@zte.com.cn
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Xiaokai Ran <ran.xiaokai@zte.com.cn>
Reviewed-by: Yang Yang <yang.yang29@zte.com.cn>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index 26853ba..0de9d33 100644 (file)
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -29,6 +29,8 @@
 
 static int ksm_fd;
 static int ksm_full_scans_fd;
+static int proc_self_ksm_stat_fd;
+static int ksm_use_zero_pages_fd;
 static int pagemap_fd;
 static size_t pagesize;
 
@@ -59,6 +61,33 @@ static bool range_maps_duplicates(char *addr, unsigned long size)
        return false;
 }
 
+static long get_my_ksm_zero_pages(void)
+{
+       char buf[200];
+       char *substr_ksm_zero;
+       size_t value_pos;
+       ssize_t read_size;
+       unsigned long my_ksm_zero_pages;
+
+       if (!proc_self_ksm_stat_fd)
+               return 0;
+
+       read_size = pread(proc_self_ksm_stat_fd, buf, sizeof(buf) - 1, 0);
+       if (read_size < 0)
+               return -errno;
+
+       buf[read_size] = 0;
+
+       substr_ksm_zero = strstr(buf, "ksm_zero_pages");
+       if (!substr_ksm_zero)
+               return 0;
+
+       value_pos = strcspn(substr_ksm_zero, "0123456789");
+       my_ksm_zero_pages = strtol(substr_ksm_zero + value_pos, NULL, 10);
+
+       return my_ksm_zero_pages;
+}
+
 static long ksm_get_full_scans(void)
 {
        char buf[10];
@@ -159,6 +188,70 @@ unmap:
        munmap(map, size);
 }
 
+static void test_unmerge_zero_pages(void)
+{
+       const unsigned int size = 2 * MiB;
+       char *map;
+       unsigned int offs;
+       unsigned long pages_expected;
+
+       ksft_print_msg("[RUN] %s\n", __func__);
+
+       if (proc_self_ksm_stat_fd < 0) {
+               ksft_test_result_skip("open(\"/proc/self/ksm_stat\") failed\n");
+               return;
+       }
+       if (ksm_use_zero_pages_fd < 0) {
+               ksft_test_result_skip("open \"/sys/kernel/mm/ksm/use_zero_pages\" failed\n");
+               return;
+       }
+       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;
+       }
+
+       /* Let KSM deduplicate zero pages. */
+       map = mmap_and_merge_range(0x00, size, false);
+       if (map == MAP_FAILED)
+               return;
+
+       /* Check if ksm_zero_pages is updated correctly after KSM merging */
+       pages_expected = size / pagesize;
+       if (pages_expected != get_my_ksm_zero_pages()) {
+               ksft_test_result_fail("'ksm_zero_pages' updated after merging\n");
+               goto unmap;
+       }
+
+       /* Try to unmerge half of the region */
+       if (madvise(map, size / 2, MADV_UNMERGEABLE)) {
+               ksft_test_result_fail("MADV_UNMERGEABLE failed\n");
+               goto unmap;
+       }
+
+       /* Check if ksm_zero_pages is updated correctly after unmerging */
+       pages_expected /= 2;
+       if (pages_expected != get_my_ksm_zero_pages()) {
+               ksft_test_result_fail("'ksm_zero_pages' updated after unmerging\n");
+               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;
+
+       /* Now we should have no zeropages remaining. */
+       if (get_my_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),
+                       "KSM zero pages were unmerged\n");
+unmap:
+       munmap(map, size);
+}
+
 static void test_unmerge_discarded(void)
 {
        const unsigned int size = 2 * MiB;
@@ -358,7 +451,7 @@ unmap:
 
 int main(int argc, char **argv)
 {
-       unsigned int tests = 5;
+       unsigned int tests = 6;
        int err;
 
 #ifdef __NR_userfaultfd
@@ -379,8 +472,11 @@ int main(int argc, char **argv)
        pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
        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);
+       ksm_use_zero_pages_fd = open("/sys/kernel/mm/ksm/use_zero_pages", O_RDWR);
 
        test_unmerge();
+       test_unmerge_zero_pages();
        test_unmerge_discarded();
 #ifdef __NR_userfaultfd
        test_unmerge_uffd_wp();