On 22/01/2026 23:18, David Hildenbrand (Red Hat) wrote: > On 1/22/26 18:02, Kevin Brodsky wrote: >> Many cow tests rely on FORCE_READ() to populate pages. Introduce a >> helper to make sure that the pages are actually populated, and fail >> otherwise. >> >> Suggested-by: David Hildenbrand (Red Hat) <[email protected]> >> Signed-off-by: Kevin Brodsky <[email protected]> >> --- >> tools/testing/selftests/mm/cow.c | 43 ++++++++++++++++++++++++-------- >> 1 file changed, 33 insertions(+), 10 deletions(-) >> >> diff --git a/tools/testing/selftests/mm/cow.c >> b/tools/testing/selftests/mm/cow.c >> index 83b3563be26b..d9c69c04b67d 100644 >> --- a/tools/testing/selftests/mm/cow.c >> +++ b/tools/testing/selftests/mm/cow.c >> @@ -75,6 +75,18 @@ static bool range_is_swapped(void *addr, size_t size) >> return true; >> } >> +static bool populate_page_checked(char *addr) >> +{ >> + bool ret; >> + >> + FORCE_READ(*addr); >> + ret = pagemap_is_populated(pagemap_fd, addr); >> + if (!ret) >> + ksft_print_msg("Failed to populate page\n"); >> + >> + return ret; >> +} > > LGTM. > > On second thought, this primarily catches if someone breaks > FORCE_READ() ... which hopefully doesn't happen that often? ;) > > Because if the read succeeded, surely there must be something in the > page tables.
Indeed, one would hope so! The check doesn't hurt either though (especially since we already have the pagemap fd around). - Kevin
