[LTP] [PATCH v4 2/2] add ksm test for smart-scan feature

[Stefan Roesch]

This adds a new ksm (kernel samepage merging) test to evaluate the new
smart scan feature. It allocates a page and fills it with 'a'
characters. It captures the pages_skipped counter, waits for a few
iterations and captures the pages_skipped counter again. The expectation
is that over 50% of the page scans are skipped (There is only one page
that has KSM enabled and it gets scanned during each iteration and it
cannot be de-duplicated).

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 runtest/mm                       |   1 +
 testcases/kernel/mem/.gitignore  |   1 +
 testcases/kernel/mem/ksm/ksm07.c | 113 +++++++++++++++++++++++++++++++
 3 files changed, 115 insertions(+)
 create mode 100644 testcases/kernel/mem/ksm/ksm07.c

diff --git a/runtest/mm b/runtest/mm
index f288fed36..d859b331c 100644
--- a/runtest/mm
+++ b/runtest/mm
@@ -70,6 +70,7 @@ ksm05 ksm05 -I 10
 ksm06 ksm06
 ksm06_1 ksm06 -n 10
 ksm06_2 ksm06 -n 8000
+ksm07 ksm07
 
 cpuset01 cpuset01
 
diff --git a/testcases/kernel/mem/.gitignore b/testcases/kernel/mem/.gitignore
index 7258489ed..c96fe8bfc 100644
--- a/testcases/kernel/mem/.gitignore
+++ b/testcases/kernel/mem/.gitignore
@@ -53,6 +53,7 @@
 /ksm/ksm04
 /ksm/ksm05
 /ksm/ksm06
+/ksm/ksm07
 /mem/mem02
 /mmapstress/mmap-corruption01
 /mmapstress/mmapstress01
diff --git a/testcases/kernel/mem/ksm/ksm07.c b/testcases/kernel/mem/ksm/ksm07.c
new file mode 100644
index 000000000..1ae5e9cd8
--- /dev/null
+++ b/testcases/kernel/mem/ksm/ksm07.c
@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2010-2023  Red Hat, Inc.
+ */
+/*\
+ * [Description]
+ *
+ * Kernel Samepage Merging (KSM) for smart scan feature
+ *
+ * Test allocates a page and fills it with 'a' characters. It captures the
+ * pages_skipped counter, waits for a few  iterations and captures the
+ * pages_skipped counter again. The expectation  is that over 50% of the page
+ * scans are skipped. (There is only one page that has KSM enabled and it gets
+ * scanned during each iteration and it cannot be de-duplicated.)
+ *
+ * Smart scan feature was added in kernel v6.7.
+ *
+ * [Prerequisites]
+ *
+ * ksm and ksmtuned daemons need to be disabled. Otherwise, it could
+ * distrub the testing as they also change some ksm tunables depends
+ * on current workloads.
+ */
+#include <sys/wait.h>
+#include "mem.h"
+
+/* This test allocates one page, fills the page with a's, captures the
+ * full_scan and pages_skipped counters. Then it makes sure at least 3
+ * full scans have been performed and measures the above counters again.
+ * The expectation is that at least 50% of the pages are skipped.
+ *
+ * To wait for at least 3 scans it uses the wait_ksmd_full_scan() function. In
+ * reality, it will be a lot more scans as the wait_ksmd_full_scan() function
+ * sleeps for one second.
+ */
+static void verify_ksm(void)
+{
+	int full_scans_begin;
+	int full_scans_end;
+	int pages_skipped_begin;
+	int pages_skipped_end;
+	int diff_pages;
+	int diff_scans;
+	unsigned long page_size;
+	char *memory;
+
+	/* Apply for the space for memory. */
+	page_size = sysconf(_SC_PAGE_SIZE);
+	memory = SAFE_MALLOC(page_size);
+	memory = SAFE_MMAP(NULL, page_size, PROT_READ|PROT_WRITE,
+					   MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
+#ifdef HAVE_DECL_MADV_MERGEABLE
+	if (madvise(memory, page_size, MADV_MERGEABLE) == -1)
+		tst_brk(TBROK|TERRNO, "madvise");
+#endif
+	memset(memory, 'a', page_size);
+
+	tst_res(TINFO, "KSM merging");
+
+	if (access(PATH_KSM "max_page_sharing", F_OK) == 0)
+		SAFE_FILE_PRINTF(PATH_KSM "run", "2");
+
+	/* Set defalut ksm scan values. */
+	SAFE_FILE_PRINTF(PATH_KSM "run", "1");
+	SAFE_FILE_PRINTF(PATH_KSM "pages_to_scan", "%ld", 100l);
+	SAFE_FILE_PRINTF(PATH_KSM "sleep_millisecs", "0");
+
+	/* Measure pages skipped aka "smart scan". */
+	SAFE_FILE_SCANF(PATH_KSM "full_scans", "%d", &full_scans_begin);
+	SAFE_FILE_SCANF(PATH_KSM "pages_skipped", "%d", &pages_skipped_begin);
+	wait_ksmd_full_scan();
+
+	tst_res(TINFO, "stop KSM");
+	SAFE_FILE_PRINTF(PATH_KSM "run", "0");
+
+	SAFE_FILE_SCANF(PATH_KSM "full_scans", "%d", &full_scans_end);
+	SAFE_FILE_SCANF(PATH_KSM "pages_skipped", "%d", &pages_skipped_end);
+	diff_pages = pages_skipped_end - pages_skipped_begin;
+	diff_scans = full_scans_end - full_scans_begin;
+
+	if (diff_pages < diff_scans * 50 / 100) {
+		tst_res(TINFO, "number of pages %d", diff_pages);
+		tst_res(TINFO, "number of scans %d", diff_scans);
+		tst_res(TFAIL, "not enough pages have been skipped by smart_scan.");
+	} else {
+		tst_res(TPASS, "smart_scan skipped more than 50%% of the pages.");
+	}
+
+#ifdef HAVE_DECL_MADV_MERGEABLE
+	if (madvise(memory, page_size, MADV_UNMERGEABLE) == -1)
+		tst_brk(TBROK|TERRNO, "madvise");
+#endif
+}
+
+static struct tst_test test = {
+	.needs_root = 1,
+	.options = (struct tst_option[]) {
+		{}
+	},
+	.save_restore = (const struct tst_path_val[]) {
+		{PATH_KSM "pages_skipped", NULL, TST_SR_TCONF},
+		{PATH_KSM "run", NULL, TST_SR_TCONF},
+		{PATH_KSM "sleep_millisecs", NULL, TST_SR_TCONF},
+		{PATH_KSM "smart_scan", "1",
+			TST_SR_SKIP_MISSING | TST_SR_TCONF},
+		{}
+	},
+	.needs_kconfigs = (const char *const[]){
+		"CONFIG_KSM=y",
+		NULL
+	},
+	.test_all = verify_ksm,
+};
-- 
2.39.3