Re: [PATCH RESEND v1 3/5] selftests/mm: skip khugepaged swap tests without swap

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

On 23/07/2026 6:08 am, Sarthak Sharma wrote:
> 
> 
> On 7/22/26 7:35 PM, Muhammad Usama Anjum wrote:
>> Hi,
>>
>> Thank you for review.
>>
>> On 22/07/2026 1:16 pm, Sarthak Sharma wrote:
>>> Hi Usama!
>>>
>>> On 7/22/26 2:41 PM, Muhammad Usama Anjum 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.
>>>>
>>>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
>>>> ---
>>>>  tools/testing/selftests/mm/khugepaged.c | 34 +++++++++++++++++++++++++
>>>>  1 file changed, 34 insertions(+)
>>>>
>>>> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
>>>> index 10e8dedcb087d..a152cec59fcbd 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;
>>>> +}
>>>> +
>>>>  static void save_settings(void)
>>>>  {
>>>>  	ksft_print_msg("Save THP and khugepaged settings...");
>>>> @@ -734,6 +756,12 @@ static void collapse_swapin_single_pte(struct collapse_context *c, struct mem_op
>>>>  {
>>>>  	void *p;
>>>>  
>>>> +	if (!is_swap_enabled()) {
>>>> +		skip("No active swap");
>>>
>>> Can we prefix this skip message with a #, as recommended for KTAP
>>> output? Right now it is printing like this:
>> It looks like `skip()` is not being prefixed with `#` in this test
>> because of how it is currently used.
>>
>> The `skip()` helper itself should probably be fixed, but that can be
>> handled in a separate follow-up patch. This test is not fully
>> TAP-compliant at the moment: the normal pass/fail output appears to be
>> compliant, while the skip-related messages are not. Would it make sense
>> to address that separately from this series?
> 
> I think there's nothing wrong with the skip() helper. Normal pass/fail
> output appears to be TAP compliant because there's a ksft_print_msg(...)
> call before calling pass()/fail() helpers. If we move the
> ksft_print_msg() line before the is_swap_enabled() check, we'll get
> output which is TAP compliant, something like this:
Makes sense. I'll fix it in the next version.

> 
> # Run test: collapse_swapin_single_pte (khugepaged:anon)
> # Swapout one page... No active swap
> ok 16 # SKIP collapse_swapin_single_pte
> #
> # Run test: collapse_swapin_single_pte (madvise:anon)
> # Swapout one page... No active swap
> ok 17 # SKIP collapse_swapin_single_pte
> #
> # Run test: collapse_max_ptes_swap (khugepaged:anon)
> # Swapout 65 of 512 pages... No active swap
> ok 18 # SKIP collapse_max_ptes_swap
> #
> # Run test: collapse_max_ptes_swap (madvise:anon)
> # Swapout 65 of 512 pages... No active swap
> ok 19 # SKIP collapse_max_ptes_swap
> 
>>
>> Also when we run the whole mm suite using ./run_vmtests.sh, it appends an extra
>> # in start of the output which we get by running normal test directly. Its
>> controversial already that we are applying TAP styling to suite level and test
>> level as well. So non-compliant skip in this test makes overall output
>> compliant.>
>>>
>>> # Run test: collapse_swapin_single_pte (khugepaged:anon)
>>>  No active swap
>>> ok 16 # SKIP collapse_swapin_single_pte
>>> #
>>> # Run test: collapse_swapin_single_pte (madvise:anon)
>>>  No active swap
>>> ok 17 # SKIP collapse_swapin_single_pte
>>> #
>>> # Run test: collapse_max_ptes_swap (khugepaged:anon)
>>>  No active swap
>>> ok 18 # SKIP collapse_max_ptes_swap
>>> #
>>> # Run test: collapse_max_ptes_swap (madvise:anon)
>>>  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);
>>>>  
>>>> @@ -760,6 +788,12 @@ 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;
>>>>  
>>>> +	if (!is_swap_enabled()) {
>>>> +		skip("No active swap");
>>>
>>> Same here.
>>>
>>>> +		ksft_test_result_report(exit_status, "%s\n", __func__);
>>>> +		return;
>>>> +	}
>>>> +
>>>>  	p = ops->setup_area(1);
>>>>  	ops->fault(p, 0, hpage_pmd_size);
>>>>  
>>>
>>
> 

-- 
Thanks,
Usama