[PATCH 1/2] kselftest: mm: prevent random failure of huge page split for khugepaged

There're some random failure for split_huge_page_test when khugepaged
collapses pages into pmd again which had split by the test.

Prevent the khugepaged's collapses for split page by setting the
mapped pmd-huge-page with MADV_NOHUGEPAGE before split.

Reported-by: Kevin Brodsky <[email protected]>
Signed-off-by: Yeoreum Yun <[email protected]>
---
 tools/testing/selftests/mm/split_huge_page_test.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 32b991472f744..99b45e5518199 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -303,6 +303,9 @@ static void verify_rss_anon_split_huge_page_all_zeroes(char *one_page, int nr_hp
 	if (!rss_anon_before)
 		ksft_exit_fail_msg("No RssAnon is allocated before split\n");
 
+	/* Prevent khugepaged from collapsing the pages. */
+	madvise(one_page, len, MADV_NOHUGEPAGE);
+
 	/* split all THPs */
 	write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
 		      (uint64_t)one_page + len, 0);
@@ -350,6 +353,9 @@ static void split_pmd_thp_to_order(int order)
 	if (!check_huge_anon(one_page, 4, pmd_pagesize))
 		ksft_exit_fail_msg("No THP is allocated\n");
 
+	/* Prevent khugepaged from collapsing the pages. */
+	madvise(one_page, len, MADV_NOHUGEPAGE);
+
 	/* split all THPs */
 	write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
 		(uint64_t)one_page + len, order);
@@ -436,6 +442,9 @@ static void split_pte_mapped_thp(void)
 		goto out;
 	}
 
+	/* Prevent khugepaged from collapsing the pages. */
+	madvise(thp_area, thp_area_size, MADV_NOHUGEPAGE);
+
 	/* Split all THPs through the remapped pages. */
 	write_debugfs(PID_FMT, getpid(), (uint64_t)page_area,
 		      (uint64_t)page_area + page_area_size, 0);
@@ -665,6 +674,8 @@ static int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size,
 		ksft_test_result_skip("Pagecache folio split skipped\n");
 		return -2;
 	}
+	/* Prevent khugepaged from collapsing the pages. */
+	madvise(*addr, fd_size, MADV_NOHUGEPAGE);
 	return 0;
 err_out_close:
 	close(*fd);

-- 
2.43.0