On 2021-08-19 21:33:43, Zhansaya Bagdauletkyzy wrote:

Since merged pages are copied every time they need to be modified, the write access time is different between shared and non-shared pages. Add ksm_cow_time() function which evaluates latency of these COW breaks. First, 4000 pages are allocated and the time, required to modify 1 byte in every other page, is measured. After this, the pages are merged into 2000 pairs and in each pair, 1 page is modified (i.e. they are decoupled) to detect COW breaks. The time needed to break COW of merged pages is then compared with performance of non-shared pages.

The test is run as follows: ./ksm_tests -C The output: Total size: 15 MiB

Not merged pages: Total time: 0.002185489 s Average speed: 3202.945 MiB/s

Merged pages: Total time: 0.004386872 s Average speed: 1595.670 MiB/s

Signed-off-by: Zhansaya Bagdauletkyzy zhansayabagdaulet@gmail.com

v2 -> v3:

• address Tyler's feedback

Thanks for incorporating my suggestions! I can confirm that my feedback was completely addressed.

Reviewed-by: Tyler Hicks tyhicks@linux.microsoft.com

Tyler

Tyler's comments: https://lkml.org/lkml/2021/8/16/931

v1 -> v2: As suggested by Pavel,

• add baseline figures with non-shared pages
• instead of having all pages merged together, create pairs of duplicated pages

Pavel's comments: https://lkml.org/lkml/2021/8/3/1363

tools/testing/selftests/vm/ksm_tests.c | 86 +++++++++++++++++++++++++- 1 file changed, 83 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/vm/ksm_tests.c b/tools/testing/selftests/vm/ksm_tests.c index 432dfe615e50..c14927417759 100644 --- a/tools/testing/selftests/vm/ksm_tests.c +++ b/tools/testing/selftests/vm/ksm_tests.c @@ -33,7 +33,8 @@ enum ksm_test_name { CHECK_KSM_UNMERGE, CHECK_KSM_ZERO_PAGE_MERGE, CHECK_KSM_NUMA_MERGE,

• KSM_MERGE_TIME

• KSM_MERGE_TIME,
• KSM_COW_TIME

}; static int ksm_write_sysfs(const char *file_path, unsigned long val) @@ -98,7 +99,8 @@ static void print_help(void) " -U (page unmerging)\n" " -P evaluate merging time and speed.\n" " For this test, the size of duplicated memory area (in MiB)\n"

•       "    must be provided using -s option\n\n");
  

•       "    must be provided using -s option\n"
  

•       " -C evaluate the time required to break COW of merged pages.\n\n");
  

printf(" -a: specify the access protections of pages.\n" " <prot> must be of the form [rwx].\n" @@ -455,6 +457,77 @@ static int ksm_merge_time(int mapping, int prot, int timeout, size_t map_size) return KSFT_FAIL; } +static int ksm_cow_time(int mapping, int prot, int timeout, size_t page_size) +{

• void *map_ptr;
• struct timespec start_time, end_time;
• unsigned long cow_time_ns;
• /* page_count must be less than 2*page_size */
• size_t page_count = 4000;
• map_ptr = allocate_memory(NULL, prot, mapping, '*', page_size * page_count);
• if (!map_ptr)

• return KSFT_FAIL;
  

• if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time)) {

• perror("clock_gettime");
  

• return KSFT_FAIL;
  

• }
• for (size_t i = 0; i < page_count - 1; i = i + 2)

• memset(map_ptr + page_size * i, '-', 1);
  

• if (clock_gettime(CLOCK_MONOTONIC_RAW, &end_time)) {

• perror("clock_gettime");
  

• return KSFT_FAIL;
  

• }
• cow_time_ns = (end_time.tv_sec - start_time.tv_sec) * NSEC_PER_SEC +

•        (end_time.tv_nsec - start_time.tv_nsec);
  

• printf("Total size: %lu MiB\n\n", (page_size * page_count) / MB);
• printf("Not merged pages:\n");
• printf("Total time: %ld.%09ld s\n", cow_time_ns / NSEC_PER_SEC,

•       cow_time_ns % NSEC_PER_SEC);
  

• printf("Average speed: %.3f MiB/s\n\n", ((page_size * (page_count / 2)) / MB) /

• 			       ((double)cow_time_ns / NSEC_PER_SEC));
  

• /* Create 2000 pairs of duplicate pages */
• for (size_t i = 0; i < page_count - 1; i = i + 2) {

• memset(map_ptr + page_size * i, '+', i / 2 + 1);
  

• memset(map_ptr + page_size * (i + 1), '+', i / 2 + 1);
  

• }
• if (ksm_merge_pages(map_ptr, page_size * page_count, start_time, timeout))

• goto err_out;
  

• if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time)) {

• perror("clock_gettime");
  

• goto err_out;
  

• }
• for (size_t i = 0; i < page_count - 1; i = i + 2)

• memset(map_ptr + page_size * i, '-', 1);
  

• if (clock_gettime(CLOCK_MONOTONIC_RAW, &end_time)) {

• perror("clock_gettime");
  

• goto err_out;
  

• }
• cow_time_ns = (end_time.tv_sec - start_time.tv_sec) * NSEC_PER_SEC +

•        (end_time.tv_nsec - start_time.tv_nsec);
  

• printf("Merged pages:\n");
• printf("Total time: %ld.%09ld s\n", cow_time_ns / NSEC_PER_SEC,

•       cow_time_ns % NSEC_PER_SEC);
  

• printf("Average speed: %.3f MiB/s\n", ((page_size * (page_count / 2)) / MB) /

• 			       ((double)cow_time_ns / NSEC_PER_SEC));
  

• munmap(map_ptr, page_size * page_count);
• return KSFT_PASS;

+err_out:

• printf("Not OK\n");
• munmap(map_ptr, page_size * page_count);
• return KSFT_FAIL;

+}

int main(int argc, char *argv[]) { int ret, opt; @@ -468,7 +541,7 @@ int main(int argc, char *argv[]) bool merge_across_nodes = KSM_MERGE_ACROSS_NODES_DEFAULT; long size_MB = 0;

• while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:MUZNP")) != -1) {

• while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:MUZNPC")) != -1) { switch (opt) { case 'a': prot = str_to_prot(optarg);

@@ -522,6 +595,9 @@ int main(int argc, char *argv[]) case 'P': test_name = KSM_MERGE_TIME; break;

• case 'C':
  

• 	test_name = KSM_COW_TIME;
  

• 	break;
  

  default: return KSFT_FAIL; }

@@ -571,6 +647,10 @@ int main(int argc, char *argv[]) ret = ksm_merge_time(MAP_PRIVATE | MAP_ANONYMOUS, prot, ksm_scan_limit_sec, size_MB); break;

• case KSM_COW_TIME:

• ret = ksm_cow_time(MAP_PRIVATE | MAP_ANONYMOUS, prot, ksm_scan_limit_sec,
  

• 		   page_size);
  

• break;
  

  }

if (ksm_restore(&ksm_sysfs_old)) { -- 2.25.1