Re: [PATCH v2 1/4] selftests: vm: add KSM merge test

From: Tyler Hicks
Date: Mon Aug 16 2021 - 10:00:07 EST

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On 2021-07-14 14:56:06, Zhansaya Bagdauletkyzy wrote:
> Add check_ksm_merge() function to check the basic merging feature of
> KSM. First, some number of identical pages are allocated and the
> MADV_MERGEABLE advice is given to merge these pages. Then, pages_shared
> and pages_sharing values are compared with the expected numbers using
> assert_ksm_pages_count() function. The number of pages can be changed
> using -p option.
>
> Signed-off-by: Zhansaya Bagdauletkyzy <zhansayabagdaulet@xxxxxxxxx>

Reviewed-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx>

As Pavel mentioned, we went through some private iterations on these
patches with Zhansaya so my review comments have already been addressed.

Tyler

> ---
> tools/testing/selftests/vm/.gitignore | 1 +
> tools/testing/selftests/vm/Makefile | 1 +
> tools/testing/selftests/vm/ksm_tests.c | 306 ++++++++++++++++++++++
> tools/testing/selftests/vm/run_vmtests.sh | 16 ++
> 4 files changed, 324 insertions(+)
> create mode 100644 tools/testing/selftests/vm/ksm_tests.c
>
> diff --git a/tools/testing/selftests/vm/.gitignore b/tools/testing/selftests/vm/.gitignore
> index f0fd80ef17df..b02eac613fdd 100644
> --- a/tools/testing/selftests/vm/.gitignore
> +++ b/tools/testing/selftests/vm/.gitignore
> @@ -27,3 +27,4 @@ hmm-tests
> memfd_secret
> local_config.*
> split_huge_page_test
> +ksm_tests
> diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
> index 521243770f26..e6f22a801b71 100644
> --- a/tools/testing/selftests/vm/Makefile
> +++ b/tools/testing/selftests/vm/Makefile
> @@ -45,6 +45,7 @@ TEST_GEN_FILES += thuge-gen
> TEST_GEN_FILES += transhuge-stress
> TEST_GEN_FILES += userfaultfd
> TEST_GEN_FILES += split_huge_page_test
> +TEST_GEN_FILES += ksm_tests
>
> ifeq ($(MACHINE),x86_64)
> CAN_BUILD_I386 := $(shell ./../x86/check_cc.sh $(CC) ../x86/trivial_32bit_program.c -m32)
> diff --git a/tools/testing/selftests/vm/ksm_tests.c b/tools/testing/selftests/vm/ksm_tests.c
> new file mode 100644
> index 000000000000..d74d5aa34b16
> --- /dev/null
> +++ b/tools/testing/selftests/vm/ksm_tests.c
> @@ -0,0 +1,306 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <sys/mman.h>
> +#include <stdbool.h>
> +#include <time.h>
> +#include <string.h>
> +
> +#include "../kselftest.h"
> +
> +#define KSM_SYSFS_PATH "/sys/kernel/mm/ksm/"
> +#define KSM_FP(s) (KSM_SYSFS_PATH s)
> +#define KSM_SCAN_LIMIT_SEC_DEFAULT 120
> +#define KSM_PAGE_COUNT_DEFAULT 10l
> +#define KSM_PROT_STR_DEFAULT "rw"
> +
> +struct ksm_sysfs {
> + unsigned long max_page_sharing;
> + unsigned long merge_across_nodes;
> + unsigned long pages_to_scan;
> + unsigned long run;
> + unsigned long sleep_millisecs;
> + unsigned long stable_node_chains_prune_millisecs;
> + unsigned long use_zero_pages;
> +};
> +
> +static int ksm_write_sysfs(const char *file_path, unsigned long val)
> +{
> + FILE *f = fopen(file_path, "w");
> +
> + if (!f) {
> + fprintf(stderr, "f %s\n", file_path);
> + perror("fopen");
> + return 1;
> + }
> + if (fprintf(f, "%lu", val) < 0) {
> + perror("fprintf");
> + return 1;
> + }
> + fclose(f);
> +
> + return 0;
> +}
> +
> +static int ksm_read_sysfs(const char *file_path, unsigned long *val)
> +{
> + FILE *f = fopen(file_path, "r");
> +
> + if (!f) {
> + fprintf(stderr, "f %s\n", file_path);
> + perror("fopen");
> + return 1;
> + }
> + if (fscanf(f, "%lu", val) != 1) {
> + perror("fscanf");
> + return 1;
> + }
> + fclose(f);
> +
> + return 0;
> +}
> +
> +static int str_to_prot(char *prot_str)
> +{
> + int prot = 0;
> +
> + if ((strchr(prot_str, 'r')) != NULL)
> + prot |= PROT_READ;
> + if ((strchr(prot_str, 'w')) != NULL)
> + prot |= PROT_WRITE;
> + if ((strchr(prot_str, 'x')) != NULL)
> + prot |= PROT_EXEC;
> +
> + return prot;
> +}
> +
> +static void print_help(void)
> +{
> + printf("usage: ksm_tests [-h] [-a prot] [-p page_count] [-l timeout]\n");
> + printf(" -a: specify the access protections of pages.\n"
> + " <prot> must be of the form [rwx].\n"
> + " Default: %s\n", KSM_PROT_STR_DEFAULT);
> + printf(" -p: specify the number of pages to test.\n"
> + " Default: %ld\n", KSM_PAGE_COUNT_DEFAULT);
> + printf(" -l: limit the maximum running time (in seconds) for a test.\n"
> + " Default: %d seconds\n", KSM_SCAN_LIMIT_SEC_DEFAULT);
> +
> + exit(0);
> +}
> +
> +static void *allocate_memory(void *ptr, int prot, int mapping, char data, size_t map_size)
> +{
> + void *map_ptr = mmap(ptr, map_size, PROT_WRITE, mapping, -1, 0);
> +
> + if (!map_ptr) {
> + perror("mmap");
> + return NULL;
> + }
> + memset(map_ptr, data, map_size);
> + if (mprotect(map_ptr, map_size, prot)) {
> + perror("mprotect");
> + munmap(map_ptr, map_size);
> + return NULL;
> + }
> +
> + return map_ptr;
> +}
> +
> +static int ksm_do_scan(int scan_count, struct timespec start_time, int timeout)
> +{
> + struct timespec cur_time;
> + unsigned long cur_scan, init_scan;
> +
> + if (ksm_read_sysfs(KSM_FP("full_scans"), &init_scan))
> + return 1;
> + cur_scan = init_scan;
> +
> + while (cur_scan < init_scan + scan_count) {
> + if (ksm_read_sysfs(KSM_FP("full_scans"), &cur_scan))
> + return 1;
> + if (clock_gettime(CLOCK_MONOTONIC_RAW, &cur_time)) {
> + perror("clock_gettime");
> + return 1;
> + }
> + if ((cur_time.tv_sec - start_time.tv_sec) > timeout) {
> + printf("Scan time limit exceeded\n");
> + return 1;
> + }
> + }
> +
> + return 0;
> +}
> +
> +static int ksm_merge_pages(void *addr, size_t size, struct timespec start_time, int timeout)
> +{
> + if (madvise(addr, size, MADV_MERGEABLE)) {
> + perror("madvise");
> + return 1;
> + }
> + if (ksm_write_sysfs(KSM_FP("run"), 1))
> + return 1;
> +
> + /* Since merging occurs only after 2 scans, make sure to get at least 2 full scans */
> + if (ksm_do_scan(2, start_time, timeout))
> + return 1;
> +
> + return 0;
> +}
> +
> +static bool assert_ksm_pages_count(long dupl_page_count)
> +{
> + unsigned long max_page_sharing, pages_sharing, pages_shared;
> +
> + if (ksm_read_sysfs(KSM_FP("pages_shared"), &pages_shared) ||
> + ksm_read_sysfs(KSM_FP("pages_sharing"), &pages_sharing) ||
> + ksm_read_sysfs(KSM_FP("max_page_sharing"), &max_page_sharing))
> + return false;
> +
> + /*
> + * Since there must be at least 2 pages for merging and 1 page can be
> + * shared with the limited number of pages (max_page_sharing), sometimes
> + * there are 'leftover' pages that cannot be merged. For example, if there
> + * are 11 pages and max_page_sharing = 10, then only 10 pages will be
> + * merged and the 11th page won't be affected. As a result, when the number
> + * of duplicate pages is divided by max_page_sharing and the remainder is 1,
> + * pages_shared and pages_sharing values will be equal between dupl_page_count
> + * and dupl_page_count - 1.
> + */
> + if (dupl_page_count % max_page_sharing == 1 || dupl_page_count % max_page_sharing == 0) {
> + if (pages_shared == dupl_page_count / max_page_sharing &&
> + pages_sharing == pages_shared * (max_page_sharing - 1))
> + return true;
> + } else {
> + if (pages_shared == (dupl_page_count / max_page_sharing + 1) &&
> + pages_sharing == dupl_page_count - pages_shared)
> + return true;
> + }
> +
> + return false;
> +}
> +
> +static int ksm_save_def(struct ksm_sysfs *ksm_sysfs)
> +{
> + if (ksm_read_sysfs(KSM_FP("max_page_sharing"), &ksm_sysfs->max_page_sharing) ||
> + ksm_read_sysfs(KSM_FP("merge_across_nodes"), &ksm_sysfs->merge_across_nodes) ||
> + ksm_read_sysfs(KSM_FP("sleep_millisecs"), &ksm_sysfs->sleep_millisecs) ||
> + ksm_read_sysfs(KSM_FP("pages_to_scan"), &ksm_sysfs->pages_to_scan) ||
> + ksm_read_sysfs(KSM_FP("run"), &ksm_sysfs->run) ||
> + ksm_read_sysfs(KSM_FP("stable_node_chains_prune_millisecs"),
> + &ksm_sysfs->stable_node_chains_prune_millisecs) ||
> + ksm_read_sysfs(KSM_FP("use_zero_pages"), &ksm_sysfs->use_zero_pages))
> + return 1;
> +
> + return 0;
> +}
> +
> +static int ksm_restore(struct ksm_sysfs *ksm_sysfs)
> +{
> + if (ksm_write_sysfs(KSM_FP("max_page_sharing"), ksm_sysfs->max_page_sharing) ||
> + ksm_write_sysfs(KSM_FP("merge_across_nodes"), ksm_sysfs->merge_across_nodes) ||
> + ksm_write_sysfs(KSM_FP("pages_to_scan"), ksm_sysfs->pages_to_scan) ||
> + ksm_write_sysfs(KSM_FP("run"), ksm_sysfs->run) ||
> + ksm_write_sysfs(KSM_FP("sleep_millisecs"), ksm_sysfs->sleep_millisecs) ||
> + ksm_write_sysfs(KSM_FP("stable_node_chains_prune_millisecs"),
> + ksm_sysfs->stable_node_chains_prune_millisecs) ||
> + ksm_write_sysfs(KSM_FP("use_zero_pages"), ksm_sysfs->use_zero_pages))
> + return 1;
> +
> + return 0;
> +}
> +
> +static int check_ksm_merge(int mapping, int prot, long page_count, int timeout, size_t page_size)
> +{
> + void *map_ptr;
> + struct timespec start_time;
> +
> + if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time)) {
> + perror("clock_gettime");
> + return KSFT_FAIL;
> + }
> +
> + /* fill pages with the same data and merge them */
> + map_ptr = allocate_memory(NULL, prot, mapping, '*', page_size * page_count);
> + if (!map_ptr)
> + return KSFT_FAIL;
> +
> + if (ksm_merge_pages(map_ptr, page_size * page_count, start_time, timeout))
> + goto err_out;
> +
> + /* verify that the right number of pages are merged */
> + if (assert_ksm_pages_count(page_count)) {
> + printf("OK\n");
> + 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;
> + int prot = 0;
> + int ksm_scan_limit_sec = KSM_SCAN_LIMIT_SEC_DEFAULT;
> + long page_count = KSM_PAGE_COUNT_DEFAULT;
> + size_t page_size = sysconf(_SC_PAGESIZE);
> + struct ksm_sysfs ksm_sysfs_old;
> +
> + while ((opt = getopt(argc, argv, "ha:p:l:")) != -1) {
> + switch (opt) {
> + case 'a':
> + prot = str_to_prot(optarg);
> + break;
> + case 'p':
> + page_count = atol(optarg);
> + if (page_count <= 0) {
> + printf("The number of pages must be greater than 0\n");
> + return KSFT_FAIL;
> + }
> + break;
> + case 'l':
> + ksm_scan_limit_sec = atoi(optarg);
> + if (ksm_scan_limit_sec <= 0) {
> + printf("Timeout value must be greater than 0\n");
> + return KSFT_FAIL;
> + }
> + break;
> + case 'h':
> + print_help();
> + break;
> + default:
> + return KSFT_FAIL;
> + }
> + }
> +
> + if (prot == 0)
> + prot = str_to_prot(KSM_PROT_STR_DEFAULT);
> +
> + if (access(KSM_SYSFS_PATH, F_OK)) {
> + printf("Config KSM not enabled\n");
> + return KSFT_SKIP;
> + }
> +
> + if (ksm_save_def(&ksm_sysfs_old)) {
> + printf("Cannot save default tunables\n");
> + return KSFT_FAIL;
> + }
> +
> + if (ksm_write_sysfs(KSM_FP("run"), 2) ||
> + ksm_write_sysfs(KSM_FP("sleep_millisecs"), 0) ||
> + ksm_write_sysfs(KSM_FP("merge_across_nodes"), 1) ||
> + ksm_write_sysfs(KSM_FP("pages_to_scan"), page_count))
> + return KSFT_FAIL;
> +
> + ret = check_ksm_merge(MAP_PRIVATE | MAP_ANONYMOUS, prot, page_count, ksm_scan_limit_sec,
> + page_size);
> +
> + if (ksm_restore(&ksm_sysfs_old)) {
> + printf("Cannot restore default tunables\n");
> + return KSFT_FAIL;
> + }
> +
> + return ret;
> +}
> diff --git a/tools/testing/selftests/vm/run_vmtests.sh b/tools/testing/selftests/vm/run_vmtests.sh
> index d09a6b71f1e9..97b6f712134d 100755
> --- a/tools/testing/selftests/vm/run_vmtests.sh
> +++ b/tools/testing/selftests/vm/run_vmtests.sh
> @@ -377,6 +377,22 @@ else
> exitcode=1
> fi
>
> +echo "-------------------------------------------------------"
> +echo "running KSM MADV_MERGEABLE test with 10 identical pages"
> +echo "-------------------------------------------------------"
> +./ksm_tests -p 10
> +ret_val=$?
> +
> +if [ $ret_val -eq 0 ]; then
> + echo "[PASS]"
> +elif [ $ret_val -eq $ksft_skip ]; then
> + echo "[SKIP]"
> + exitcode=$ksft_skip
> +else
> + echo "[FAIL]"
> + exitcode=1
> +fi
> +
> exit $exitcode
>
> exit $exitcode
> --
> 2.25.1
>

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