On Fri, Aug 28, 2026 at 09:11:33AM +0100, Yeoreum Yun wrote:
> 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]>
> Reviewed-by: Zi Yan <[email protected]>
> Signed-off-by: Yeoreum Yun <[email protected]>
> ---
> tools/testing/selftests/mm/split_huge_page_test.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c
> b/tools/testing/selftests/mm/split_huge_page_test.c
> index 86a603692826..c718269a291f 100644
> --- a/tools/testing/selftests/mm/split_huge_page_test.c
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -180,6 +180,10 @@ 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. */
> + if (madvise(one_page, len, MADV_NOHUGEPAGE))
> + ksft_print_msg("madvise(MADV_NOHUGEPAGE) failed\n");
This should probably terminate the test no? There's no reason to expect this to
fail and it's better to fail then to risk a flake :)
> +
> /* split all THPs */
> write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
> (uint64_t)one_page + len, 0);
> @@ -227,6 +231,10 @@ 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");
>
> + /* Prevent khugepaged from collapsing the pages. */
> + if (madvise(one_page, len, MADV_NOHUGEPAGE))
> + ksft_print_msg("madvise(MADV_NOHUGEPAGE) failed\n");
> +
Same comment as above, also since this is a repeated pattern, I think it's worth
abstracting it like:
static void madv_nohuge(char *ptr, size_t len)
{
if (!madvise(ptr, len, MADV_NOHUGEPAGE))
return;
ksft_exit_fail_msg("MADV_NOHUGEPAGE failed, err=%d\n", errno);
}
> /* split all THPs */
> write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
> (uint64_t)one_page + len, order);
> @@ -313,6 +321,10 @@ static void split_pte_mapped_thp(void)
> goto out;
> }
>
> + /* Prevent khugepaged from collapsing the pages. */
> + if (madvise(thp_area, thp_area_size, MADV_NOHUGEPAGE))
> + ksft_print_msg("madvise(MADV_NOHUGEPAGE) failed\n");
> +
> /* Split all THPs through the remapped pages. */
> write_debugfs(PID_FMT, getpid(), (uint64_t)page_area,
> (uint64_t)page_area + page_area_size, 0);
> @@ -542,6 +554,9 @@ 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. */
> + if (madvise(*addr, fd_size, MADV_NOHUGEPAGE))
> + ksft_print_msg("madvise(MADV_NOHUGEPAGE) failed\n");
Obviously same comments re: this and above
> return 0;
> err_out_close:
> close(*fd);
>
> --
> 2.43.0
>
--
Cheers, Lorenzo
