[PATCH v7 08/10] selftests/mm/khugepaged: Enlighten for small-sized THP

[Ryan Roberts <ryan.roberts@arm.com>]

The `collapse_max_ptes_none` test was previously failing when
small-sized THP had enabled="always". The root cause is because the test
faults in 1 page less than the threshold it set for collapsing. But when
using small-sized THP we "over allocate" and therefore the threshold is
passed, and collapse unexpectedly succeeds.

Solve this by enlightening khugepaged selftest. Add a command line
option to pass in the desired small-sized THP that should be used for
all anonymous allocations. The harness will then explicitly configure
small-sized THP as requested and modify the `collapse_max_ptes_none`
test so that it faults in the threshold minus the number of pages in the
configured small-sized THP. If no command line option is provided,
default to order 0, as per previous behaviour.

I chose to use an order in the command line interface, since this makes
the interface agnostic of base page size, making it easier to invoke
from run_vmtests.sh.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
 tools/testing/selftests/mm/khugepaged.c   | 48 +++++++++++++++++------
 tools/testing/selftests/mm/run_vmtests.sh |  2 +
 2 files changed, 39 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 473ba095cffd..4d24f2eb158e 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -28,6 +28,7 @@
 static unsigned long hpage_pmd_size;
 static unsigned long page_size;
 static int hpage_pmd_nr;
+static int anon_order;
 
 #define PID_SMAPS "/proc/self/smaps"
 #define TEST_FILE "collapse_test_file"
@@ -607,6 +608,11 @@ static bool is_tmpfs(struct mem_ops *ops)
 	return ops == &__file_ops && finfo.type == VMA_SHMEM;
 }
 
+static bool is_anon(struct mem_ops *ops)
+{
+	return ops == &__anon_ops;
+}
+
 static void alloc_at_fault(void)
 {
 	struct thp_settings settings = *thp_current_settings();
@@ -673,6 +679,7 @@ static void collapse_max_ptes_none(struct collapse_context *c, struct mem_ops *o
 	int max_ptes_none = hpage_pmd_nr / 2;
 	struct thp_settings settings = *thp_current_settings();
 	void *p;
+	int fault_nr_pages = is_anon(ops) ? 1 << anon_order : 1;
 
 	settings.khugepaged.max_ptes_none = max_ptes_none;
 	thp_push_settings(&settings);
@@ -686,10 +693,10 @@ static void collapse_max_ptes_none(struct collapse_context *c, struct mem_ops *o
 		goto skip;
 	}
 
-	ops->fault(p, 0, (hpage_pmd_nr - max_ptes_none - 1) * page_size);
+	ops->fault(p, 0, (hpage_pmd_nr - max_ptes_none - fault_nr_pages) * page_size);
 	c->collapse("Maybe collapse with max_ptes_none exceeded", p, 1,
 		    ops, !c->enforce_pte_scan_limits);
-	validate_memory(p, 0, (hpage_pmd_nr - max_ptes_none - 1) * page_size);
+	validate_memory(p, 0, (hpage_pmd_nr - max_ptes_none - fault_nr_pages) * page_size);
 
 	if (c->enforce_pte_scan_limits) {
 		ops->fault(p, 0, (hpage_pmd_nr - max_ptes_none) * page_size);
@@ -1076,7 +1083,7 @@ static void madvise_retracted_page_tables(struct collapse_context *c,
 
 static void usage(void)
 {
-	fprintf(stderr, "\nUsage: ./khugepaged <test type> [dir]\n\n");
+	fprintf(stderr, "\nUsage: ./khugepaged [OPTIONS] <test type> [dir]\n\n");
 	fprintf(stderr, "\t<test type>\t: <context>:<mem_type>\n");
 	fprintf(stderr, "\t<context>\t: [all|khugepaged|madvise]\n");
 	fprintf(stderr, "\t<mem_type>\t: [all|anon|file|shmem]\n");
@@ -1085,15 +1092,34 @@ static void usage(void)
 	fprintf(stderr,	"\tCONFIG_READ_ONLY_THP_FOR_FS=y\n");
 	fprintf(stderr, "\n\tif [dir] is a (sub)directory of a tmpfs mount, tmpfs must be\n");
 	fprintf(stderr,	"\tmounted with huge=madvise option for khugepaged tests to work\n");
+	fprintf(stderr,	"\n\tSupported Options:\n");
+	fprintf(stderr,	"\t\t-h: This help message.\n");
+	fprintf(stderr,	"\t\t-s: Small-sized THP size, expressed as page order.\n");
+	fprintf(stderr,	"\t\t    Defaults to 0. Use this size for anon allocations.\n");
 	exit(1);
 }
 
-static void parse_test_type(int argc, const char **argv)
+static void parse_test_type(int argc, char **argv)
 {
+	int opt;
 	char *buf;
 	const char *token;
 
-	if (argc == 1) {
+	while ((opt = getopt(argc, argv, "s:h")) != -1) {
+		switch (opt) {
+		case 's':
+			anon_order = atoi(optarg);
+			break;
+		case 'h':
+		default:
+			usage();
+		}
+	}
+
+	argv += optind;
+	argc -= optind;
+
+	if (argc == 0) {
 		/* Backwards compatibility */
 		khugepaged_context =  &__khugepaged_context;
 		madvise_context =  &__madvise_context;
@@ -1101,7 +1127,7 @@ static void parse_test_type(int argc, const char **argv)
 		return;
 	}
 
-	buf = strdup(argv[1]);
+	buf = strdup(argv[0]);
 	token = strsep(&buf, ":");
 
 	if (!strcmp(token, "all")) {
@@ -1135,11 +1161,13 @@ static void parse_test_type(int argc, const char **argv)
 	if (!file_ops)
 		return;
 
-	if (argc != 3)
+	if (argc != 2)
 		usage();
+
+	get_finfo(argv[1]);
 }
 
-int main(int argc, const char **argv)
+int main(int argc, char **argv)
 {
 	int hpage_pmd_order;
 	struct thp_settings default_settings = {
@@ -1164,9 +1192,6 @@ int main(int argc, const char **argv)
 
 	parse_test_type(argc, argv);
 
-	if (file_ops)
-		get_finfo(argv[2]);
-
 	setbuf(stdout, NULL);
 
 	page_size = getpagesize();
@@ -1183,6 +1208,7 @@ int main(int argc, const char **argv)
 	default_settings.khugepaged.max_ptes_shared = hpage_pmd_nr / 2;
 	default_settings.khugepaged.pages_to_scan = hpage_pmd_nr * 8;
 	default_settings.hugepages[hpage_pmd_order].enabled = THP_GLOBAL;
+	default_settings.hugepages[anon_order].enabled = THP_ALWAYS;
 
 	save_settings();
 	thp_push_settings(&default_settings);
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 00757445278e..f3fa2238daef 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -359,6 +359,8 @@ CATEGORY="cow" run_test ./cow
 
 CATEGORY="thp" run_test ./khugepaged
 
+CATEGORY="thp" run_test ./khugepaged -s 2
+
 CATEGORY="thp" run_test ./transhuge-stress -d 20
 
 CATEGORY="thp" run_test ./split_huge_page_test
-- 
2.25.1