On 7/15/26 16:47, Dev Jain wrote: > > > On 15/07/26 7:39 pm, David Hildenbrand (Arm) wrote: >> On 7/15/26 15:34, Jaeyeon Lee wrote: >>> The collapse_swapin_single_pte and collapse_max_ptes_swap tests use >>> MADV_PAGEOUT to swap out pages before verifying khugepaged collapse >>> behavior. On systems without swap configured, MADV_PAGEOUT succeeds >>> but the pages are not actually swapped out, so check_swap() returns >>> false and the tests report a failure. >>> >>> These tests cannot run meaningfully without swap, so a missing swap >>> area is an environment limitation rather than a test failure. Detect >>> the absence of swap via /proc/swaps and skip the affected tests >>> instead of failing them. >>> >>> Signed-off-by: Jaeyeon Lee <[email protected]> >>> --- >>> tools/testing/selftests/mm/khugepaged.c | 25 +++++++++++++++++++++++++ >>> 1 file changed, 25 insertions(+) >>> >>> diff --git a/tools/testing/selftests/mm/khugepaged.c >>> b/tools/testing/selftests/mm/khugepaged.c >>> index 10e8dedcb087..f9b4ebe733ce 100644 >>> --- a/tools/testing/selftests/mm/khugepaged.c >>> +++ b/tools/testing/selftests/mm/khugepaged.c >>> @@ -100,6 +100,22 @@ static void skip(const char *msg) >>> exit_status = KSFT_SKIP; >>> } >>> >>> +static bool swap_available(void) >>> +{ >>> + char buf[256]; >>> + bool ret; >>> + FILE *fp = fopen("/proc/swaps", "r"); >>> + >>> + if (!fp) >>> + return false; >>> + >>> + fgets(buf, sizeof(buf), fp); >>> + ret = !!fgets(buf, sizeof(buf), fp); >>> + >>> + fclose(fp); >>> + return ret; >>> +} >>> + >> >> That doesn't mean that swapout will succeed. >> >> Take a look at cow.c where we use pagemap_is_swapped() after MADV_PAGEOUT. > > That suffers from the reverse problem - in case of a real swap bug, cow.c > will skip the test and anyone running the test won't bother.
Yes, because there could be other reasons why MADV_PAGEOUT would not be successful (speculative page references, out of swap space). > > I think this patch idea is reasonable, we need a way to say "swap definitely > won't succeed because there is no swap device, so skip" vs "swap failed, > need to dig in!" . I would not pack a "let's test if swapping in the system even works" into a khugeapged test. I think we can reasonably assume here "swap subsystem is not completely broken". And if we want to check for that, have a separate test that stresses swapping, if available. -- Cheers, David
