[PATCH v3 12/12] selftests/vm: add test to verify recollapse of THPs

["Zach O'Keefe" <zokeefe@google.com>]

Add selftest specific to madvise collapse context that tests
MADV_COLLAPSE is "successful" if a hugepage-algined/sized region is
already pmd-mapped.

Signed-off-by: Zach O'Keefe <zokeefe@google.com>
---
 tools/testing/selftests/vm/khugepaged.c | 32 +++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/tools/testing/selftests/vm/khugepaged.c b/tools/testing/selftests/vm/khugepaged.c
index e0ccc9443f78..c36d04218083 100644
--- a/tools/testing/selftests/vm/khugepaged.c
+++ b/tools/testing/selftests/vm/khugepaged.c
@@ -969,6 +969,32 @@ static void collapse_max_ptes_shared(struct collapse_context *context)
 	munmap(p, hpage_pmd_size);
 }
 
+static void madvise_collapse_existing_thps(void)
+{
+	void *p;
+	int err;
+
+	p = alloc_mapping();
+	fill_memory(p, 0, hpage_pmd_size);
+
+	printf("Collapse fully populated PTE table...");
+	madvise(p, hpage_pmd_size, MADV_HUGEPAGE);
+	err = madvise(p, hpage_pmd_size, MADV_COLLAPSE);
+	if (err == 0 && check_huge(p)) {
+		success("OK");
+		printf("Re-collapse PMD-mapped hugepage");
+		err = madvise(p, hpage_pmd_size, MADV_COLLAPSE);
+		if (err == 0 && check_huge(p))
+			success("OK");
+		else
+			fail("Fail");
+	} else {
+		fail("Fail");
+	}
+	validate_memory(p, 0, hpage_pmd_size);
+	munmap(p, hpage_pmd_size);
+}
+
 static void madvise_collapse(const char *msg, char *p, bool expect)
 {
 	int ret;
@@ -1097,6 +1123,7 @@ int main(void)
 
 	alloc_at_fault();
 
+	/* Shared tests */
 	for (i = 0; i < sizeof(contexts) / sizeof(contexts[0]); ++i) {
 		struct collapse_context *c = &contexts[i];
 
@@ -1119,5 +1146,10 @@ int main(void)
 			break;
 	}
 
+	/* madvise-specific tests */
+	disable_khugepaged();
+	madvise_collapse_existing_thps();
+	enable_khugepaged();
+
 	restore_settings(0);
 }
-- 
2.36.0.rc2.479.g8af0fa9b8e-goog