Re: [PATCH v3 3/5] selftests/mm: skip khugepaged swap tests without swap

[Usama Arif]

On Mon, 27 Jul 2026 10:52:19 +0100 Muhammad Usama Anjum <usama.anjum@xxxxxxx> wrote:

> collapse_swapin_single_pte and collapse_max_ptes_swap require
> MADV_PAGEOUT to replace anonymous pages with swap entries. On swapless
> systems there is no backing store with which to create those entries,
> so check_swap() reports missing setup rather than broken khugepaged
> behavior.
> 
> Swapless configurations are common on Android and other constrained
> test devices. Failing these cases obscures actionable results from the
> rest of the khugepaged suite.
> 
> Check /proc/swaps before either swap-dependent case and skip when no
> active swap area exists. With swap present, retain the existing
> MADV_PAGEOUT and swap-entry assertions unchanged.
> 
> Print each existing swapout diagnostic before the prerequisite check
> so skip() completes a KTAP diagnostic line instead of emitting an
> unprefixed message.
> 
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>
> ---
> Changes since v1:
> - Print swapout diagnostics before reporting no-swap skips.
> ---
>  tools/testing/selftests/mm/khugepaged.c | 38 +++++++++++++++++++++++--
>  1 file changed, 36 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
> index 10e8dedcb087d..54e888eb48bbc 100644
> --- a/tools/testing/selftests/mm/khugepaged.c
> +++ b/tools/testing/selftests/mm/khugepaged.c
> @@ -100,6 +100,28 @@ static void skip(const char *msg)
>  	exit_status = KSFT_SKIP;
>  }
>  
> +static bool is_swap_enabled(void)
> +{
> +	char buf[MAX_LINE_LENGTH];
> +	FILE *file;
> +	bool enabled = false;
> +
> +	file = fopen("/proc/swaps", "r");
> +	if (!file)
> +		return false;
> +
> +	if (!fgets(buf, sizeof(buf), file))
> +		goto out;
> +
> +	/* Check for first active swap entry. */
> +	if (fgets(buf, sizeof(buf), file))
> +		enabled = true;
> +
> +out:
> +	fclose(file);
> +	return enabled;
> +}
> +

Could is_swap_enabled() be moved to vm_util.c. This will definitely be reusable
in other places.

>  static void save_settings(void)
>  {
>  	ksft_print_msg("Save THP and khugepaged settings...");
> @@ -734,10 +756,16 @@ static void collapse_swapin_single_pte(struct collapse_context *c, struct mem_op
>  {
>  	void *p;
>  
> +	ksft_print_msg("Swapout one page...");
> +	if (!is_swap_enabled()) {
> +		skip("No active swap");
> +		ksft_test_result_report(exit_status, "%s\n", __func__);
> +		return;
> +	}
> +
>  	p = ops->setup_area(1);
>  	ops->fault(p, 0, hpage_pmd_size);
>  
> -	ksft_print_msg("Swapout one page...");
>  	if (madvise(p, page_size, MADV_PAGEOUT))
>  		ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
>  	if (check_swap(p, page_size)) {
> @@ -760,10 +788,16 @@ static void collapse_max_ptes_swap(struct collapse_context *c, struct mem_ops *o
>  	int max_ptes_swap = thp_read_num("khugepaged/max_ptes_swap");
>  	void *p;
>  
> +	ksft_print_msg("Swapout %d of %d pages...", max_ptes_swap + 1, hpage_pmd_nr);
> +	if (!is_swap_enabled()) {
> +		skip("No active swap");
> +		ksft_test_result_report(exit_status, "%s\n", __func__);
> +		return;
> +	}
> +
>  	p = ops->setup_area(1);
>  	ops->fault(p, 0, hpage_pmd_size);
>  
> -	ksft_print_msg("Swapout %d of %d pages...", max_ptes_swap + 1, hpage_pmd_nr);
>  	if (madvise(p, (max_ptes_swap + 1) * page_size, MADV_PAGEOUT))
>  		ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
>  	if (check_swap(p, (max_ptes_swap + 1) * page_size)) {
> -- 
> 2.47.3
> 
>