1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Copyright (C) 2023 Red Hat, Inc.
4 */
5 /*\
6 * [Description]
7 *
8 * Kernel Samepage Merging (KSM) for smart scan feature
9 *
10 * Test allocates a page and fills it with 'a' characters. It captures the
11 * pages_skipped counter, waits for a few iterations and captures the
12 * pages_skipped counter again. The expectation is that over 50% of the page
13 * scans are skipped. (There is only one page that has KSM enabled and it gets
14 * scanned during each iteration and it cannot be de-duplicated.)
15 *
16 * Smart scan feature was added in kernel v6.7.
17 *
18 * [Prerequisites]
19 *
20 * ksm and ksmtuned daemons need to be disabled. Otherwise, it could
21 * distrub the testing as they also change some ksm tunables depends
22 * on current workloads.
23 */
24
25 #include <sys/wait.h>
26 #include "mem.h"
27
28 /* This test allocates one page, fills the page with a's, captures the
29 * full_scan and pages_skipped counters. Then it makes sure at least 3
30 * full scans have been performed and measures the above counters again.
31 * The expectation is that at least 50% of the pages are skipped.
32 *
33 * To wait for at least 3 scans it uses the wait_ksmd_full_scan() function. In
34 * reality, it will be a lot more scans as the wait_ksmd_full_scan() function
35 * sleeps for one second.
36 */
verify_ksm(void)37 static void verify_ksm(void)
38 {
39 int full_scans_begin;
40 int full_scans_end;
41 int pages_skipped_begin;
42 int pages_skipped_end;
43 int diff_pages;
44 int diff_scans;
45 unsigned long page_size;
46 char *memory;
47
48 /* Apply for the space for memory. */
49 page_size = sysconf(_SC_PAGE_SIZE);
50 memory = SAFE_MALLOC(page_size);
51 memory = SAFE_MMAP(NULL, page_size, PROT_READ|PROT_WRITE,
52 MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
53 #ifdef HAVE_DECL_MADV_MERGEABLE
54 if (madvise(memory, page_size, MADV_MERGEABLE) == -1)
55 tst_brk(TBROK|TERRNO, "madvise");
56 #endif
57 memset(memory, 'a', page_size);
58
59 tst_res(TINFO, "KSM merging");
60
61 if (access(PATH_KSM "max_page_sharing", F_OK) == 0)
62 SAFE_FILE_PRINTF(PATH_KSM "run", "2");
63
64 /* Set defalut ksm scan values. */
65 SAFE_FILE_PRINTF(PATH_KSM "run", "1");
66 SAFE_FILE_PRINTF(PATH_KSM "pages_to_scan", "%ld", 100l);
67 SAFE_FILE_PRINTF(PATH_KSM "sleep_millisecs", "0");
68
69 /* Measure pages skipped aka "smart scan". */
70 SAFE_FILE_SCANF(PATH_KSM "full_scans", "%d", &full_scans_begin);
71 SAFE_FILE_SCANF(PATH_KSM "pages_skipped", "%d", &pages_skipped_begin);
72 wait_ksmd_full_scan();
73
74 tst_res(TINFO, "stop KSM");
75 SAFE_FILE_PRINTF(PATH_KSM "run", "0");
76
77 SAFE_FILE_SCANF(PATH_KSM "full_scans", "%d", &full_scans_end);
78 SAFE_FILE_SCANF(PATH_KSM "pages_skipped", "%d", &pages_skipped_end);
79 diff_pages = pages_skipped_end - pages_skipped_begin;
80 diff_scans = full_scans_end - full_scans_begin;
81
82 if (diff_pages < diff_scans * 50 / 100) {
83 tst_res(TINFO, "number of pages %d", diff_pages);
84 tst_res(TINFO, "number of scans %d", diff_scans);
85 tst_res(TFAIL, "not enough pages have been skipped by smart_scan");
86 } else {
87 tst_res(TPASS, "smart_scan skipped more than 50%% of the pages");
88 }
89
90 #ifdef HAVE_DECL_MADV_MERGEABLE
91 if (madvise(memory, page_size, MADV_UNMERGEABLE) == -1)
92 tst_brk(TBROK|TERRNO, "madvise");
93 #endif
94 }
95
96 static struct tst_test test = {
97 .needs_root = 1,
98 .options = (struct tst_option[]) {
99 {}
100 },
101 .save_restore = (const struct tst_path_val[]) {
102 {PATH_KSM "pages_skipped", NULL, TST_SR_TCONF},
103 {PATH_KSM "run", NULL, TST_SR_TCONF},
104 {PATH_KSM "sleep_millisecs", NULL, TST_SR_TCONF},
105 {PATH_KSM "smart_scan", "1",
106 TST_SR_SKIP_MISSING | TST_SR_TCONF},
107 {}
108 },
109 .needs_kconfigs = (const char *const[]){
110 "CONFIG_KSM=y",
111 NULL
112 },
113 .test_all = verify_ksm,
114 };
115