Re: [PATCH v5 6/6] selftest: add testing unsharing and counting ksm zero page
From: David Hildenbrand
Date: Wed Jan 18 2023 - 09:38:51 EST
On 30.12.22 02:18, yang.yang29@xxxxxxxxxx wrote:
From: xu xin <xu.xin16@xxxxxxxxxx>
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 three subjct test objects:
1) whether the count of ksm zero page can react correctly to cow
(copy on write);
2) whether the count of ksm zero page can react correctly to unmerge;
3) whether ksm zero pages are really unmerged.
Signed-off-by: xu xin <xu.xin16@xxxxxxxxxx>
Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Xuexin Jiang <jiang.xuexin@xxxxxxxxxx>
Reviewed-by: Xiaokai Ran <ran.xiaokai@xxxxxxxxxx>
Reviewed-by: Yang Yang <yang.yang29@xxxxxxxxxx>
v4->v5:
fix error of "} while (end_scans < start_scans + 20);" to
"} while (end_scans < start_scans + 2);" in wait_two_full_scans().
---
tools/testing/selftests/vm/ksm_functional_tests.c | 103 +++++++++++++++++++++-
1 file changed, 99 insertions(+), 4 deletions(-)
diff --git a/tools/testing/selftests/vm/ksm_functional_tests.c b/tools/testing/selftests/vm/ksm_functional_tests.c
index b11b7e5115dc..b792798a54c4 100644
--- a/tools/testing/selftests/vm/ksm_functional_tests.c
+++ b/tools/testing/selftests/vm/ksm_functional_tests.c
@@ -27,6 +27,8 @@
static int ksm_fd;
static int ksm_full_scans_fd;
+static int ksm_zero_pages_fd;
+static int ksm_use_zero_pages_fd;
If they are global, open them from main(), not from the test case.
static int pagemap_fd;
static size_t pagesize;
@@ -57,6 +59,22 @@ static bool range_maps_duplicates(char *addr, unsigned long size)
return false;
}
+static bool check_ksm_zero_pages_count(unsigned long zero_size)
+{
+ unsigned long pages_expected = zero_size / (4 * KiB);
+ char buf[20];
+ ssize_t read_size;
+ unsigned long ksm_zero_pages;
+
+ read_size = pread(ksm_zero_pages_fd, buf, sizeof(buf) - 1, 0);
+ if (read_size < 0)
+ return -errno;
+ buf[read_size] = 0;
+ ksm_zero_pages = strtol(buf, NULL, 10);
+
+ return ksm_zero_pages == pages_expected;
Better call this function "ksm_get_zero_pages", do it similarly to
ksm_get_full_scans() and do the comparison in the kernel.
+}
+
static long ksm_get_full_scans(void)
{
char buf[10];
@@ -70,15 +88,12 @@ static long ksm_get_full_scans(void)
return strtol(buf, NULL, 10);
}
-static int ksm_merge(void)
+static int wait_two_full_scans(void)
{
long start_scans, end_scans;
- /* Wait for two full scans such that any possible merging happened. */
start_scans = ksm_get_full_scans();
if (start_scans < 0)
- return start_scans;
- if (write(ksm_fd, "1", 1) != 1)
return -errno;
This change might not be required.
do {
end_scans = ksm_get_full_scans();
@@ -89,6 +104,34 @@ static int ksm_merge(void)
return 0;
}
+static inline int ksm_merge(void)
+{
+ /* Wait for two full scans such that any possible merging happened. */
+ if (write(ksm_fd, "1", 1) != 1)
+ return -errno;
+ return wait_two_full_scans();
+}
+
+static inline int make_cow(char *map, char val, unsigned long size)
+{
+
+ memset(map, val, size);
+ return wait_two_full_scans();
Why is that required?
+}
+
+static int unmerge_zero_page(char *start, unsigned long size)
+{
+ int ret;
+
+ ret = madvise(start, size, MADV_UNMERGEABLE);
+ if (ret) {
+ ksft_test_result_fail("MADV_UNMERGEABLE failed\n");
+ return ret;
+ }
+
+ return wait_two_full_scans();
Dito, why is that required when unmerging?
+}
+
static char *mmap_and_merge_range(char val, unsigned long size)
{
char *map;
@@ -146,6 +189,56 @@ static void test_unmerge(void)
munmap(map, size);
}
+static void test_unmerge_zero_pages(void)
+{
+ const unsigned int size = 2 * MiB;
+ char *map;
+
+ ksft_print_msg("[RUN] %s\n", __func__);
+
+ /* Confirm the interfaces*/
+ ksm_zero_pages_fd = open("/sys/kernel/mm/ksm/zero_pages_sharing", O_RDONLY);
+ if (ksm_zero_pages_fd < 0) {
+ ksft_test_result_skip("open(\"/sys/kernel/mm/ksm/zero_pages_sharing\") failed\n");
+ return;
+ }
+ ksm_use_zero_pages_fd = open("/sys/kernel/mm/ksm/use_zero_pages", O_RDWR);
+ 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;
+ }
+
+ /* Mmap zero pages*/
+ map = mmap_and_merge_range(0x00, size);
Not checking for map == MAP_FAILED. Best to follow what
test_unmerge() does.
+
+ /* Case 1: make Writing on ksm zero pages (COW) */
+ if (make_cow(map, 0xcf, size / 2)) {
+ ksft_test_result_fail("COW failed\n");
+ goto unmap;
+ }
+ ksft_test_result(check_ksm_zero_pages_count(size / 2),
+ "zero page count react to cow\n");
+
Let's keep COW tests to cow.c and focus on explicit unmerging here. Once
we add support for KSM in cow.c , we can also test that e.g., long-term
R/O pinning works as expected. I have that on my todo list but would be
pleasantly surprised if someone else could tackle it :)
+ /* Case 2: Call madvise(xxx, MADV_UNMERGEABLE)*/
+ if (unmerge_zero_page(map + size / 2, size / 4)) {
+ ksft_test_result_fail("unmerge_zero_page failed\n");
+ goto unmap;
+ }
Just avoid that helper and do it like test_unmerge(). Keep it simple.
+ ksft_test_result(check_ksm_zero_pages_count(size / 4),
+ "zero page count react to unmerge\n");
+
+ /*Check if ksm pages are really unmerged */
Missing space at the beginning. + the comment is superfluous.
+ ksft_test_result(!range_maps_duplicates(map + size / 2, size / 4),
+ "KSM zero pages were unmerged\n");
+
+unmap:
+ munmap(map, size);
+}
+
static void test_unmerge_discarded(void)
{
const unsigned int size = 2 * MiB;
@@ -261,11 +354,13 @@ int main(int argc, char **argv)
ksm_full_scans_fd = open("/sys/kernel/mm/ksm/full_scans", O_RDONLY);
if (ksm_full_scans_fd < 0)
ksft_exit_skip("open(\"/sys/kernel/mm/ksm/full_scans\") failed\n");
+
Unrelated change.
pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
if (pagemap_fd < 0)
ksft_exit_skip("open(\"/proc/self/pagemap\") failed\n");
test_unmerge();
+ test_unmerge_zero_pages();
test_unmerge_discarded();
#ifdef __NR_userfaultfd
test_unmerge_uffd_wp();
--
Thanks,
David / dhildenb