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

[Muhammad Usama Anjum <usama.anjum@arm.com>]

On 27/07/2026 6:18 pm, Usama Arif wrote:
> On Mon, 27 Jul 2026 10:52:19 +0100 Muhammad Usama Anjum <usama.anjum@arm.com> 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@arm.com>
>> ---
>> 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.
Thank you for the suggestion. There isn't any user of this at this time. But
its always better to have such functions in general library. I would prefer to
keep it local for now. If another revision is needed, I can move it then.

> 
>>  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
>>
>>

-- 
Thanks,
Usama