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

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

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:

# 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);
>>>  
>>
>