Re: [PATCH v8 1/4] kselftest: mm: prevent random failure of huge page split for khugepaged

[Sarthak Sharma <sarthak.sharma@arm.com>]

On 9/25/26 12:41 AM, 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.
> 
> Suggested-by: Kevin Brodsky <kevin.brodsky@arm.com>
> Suggested-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
> Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Acked-by: David Hildenbrand (Arm) <david@kernel.org>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>  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 c5d96a4b1db3..ef4058662b91 100644
> --- a/tools/testing/selftests/mm/split_huge_page_test.c
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -108,6 +108,18 @@ 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

Should it be "collapsing pages in range into THPs" instead?

> +	 * pages remain.
> +	 */
> +	if (!madvise(addr, len, MADV_NOHUGEPAGE))
> +		return;
> +
> +	ksft_exit_fail_msg("MADV_NOHUGEPAGE failed, err=%d\n", errno);

I feel a ksft_exit_fail_perror() would be better here, since it will
automatically print strerror(errno) as well. Still, it is not something
that should require a respin of its own, so if you plan to respin for
some other changes, you might fold these changes in as well.

Rest looks good, so:

Reviewed-by: Sarthak Sharma <sarthak.sharma@arm.com>

> +}
> +
>  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;
> @@ -120,6 +132,8 @@ 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);
> @@ -167,6 +181,8 @@ 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);
> @@ -215,6 +231,8 @@ 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
> @@ -482,6 +500,7 @@ 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);
>