[PATCH v5 1/3] kselftest: mm: prevent random failure of huge page split for khugepaged

[Yeoreum Yun]

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.

Suggested-by: Kevin Brodsky <kevin.brodsky@xxxxxxx>
Suggested-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
---
 tools/testing/selftests/mm/split_huge_page_test.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index c01d227d7fd6..cba327f77873 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -167,6 +167,18 @@ static char *allocate_zero_filled_hugepage(size_t len)
 	return result;
 }
 
+static void disable_khugepaged(void *addr, size_t len)
+{
+	/*
+	 * Disables khugepaged from collapsing THPs in range, existing THP
+	 * pages remain.
+	 */
+	if (!madvise(addr, len, MADV_NOHUGEPAGE))
+		return;
+
+	ksft_exit_fail_msg("MADV_NOHUGEPAGE failed, err=%d\n", errno);
+}
+
 static void verify_rss_anon_split_huge_page_all_zeroes(char *one_page, int nr_hpages, size_t len)
 {
 	unsigned long rss_anon_before, rss_anon_after;
@@ -179,6 +191,8 @@ 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");
 
+	disable_khugepaged(one_page, len);
+
 	/* split all THPs */
 	write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
 		      (uint64_t)one_page + len, 0);
@@ -226,6 +240,8 @@ static void split_pmd_thp_to_order(int order)
 	if (!check_huge_anon(one_page, 4 * pmd_pagesize, 4, pmd_pagesize))
 		ksft_exit_fail_msg("No THP is allocated\n");
 
+	disable_khugepaged(one_page, len);
+
 	/* split all THPs */
 	write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
 		(uint64_t)one_page + len, order);
@@ -274,6 +290,8 @@ static void split_pte_mapped_thp(void)
 		goto out;
 	}
 
+	disable_khugepaged(thp_area, thp_area_size);
+
 	/*
 	 * To challenge spitting code, we will mremap a single page of each
 	 * THP (page[i] of thp[i]) in the thp_area into page_area. This will
@@ -541,6 +559,7 @@ 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;
 	}
+	disable_khugepaged(*addr, fd_size);
 	return 0;
 err_out_close:
 	close(*fd);

-- 
2.43.0