From: "Kiryl Shutsemau (Meta)" <[email protected]> The page cache caps folio order at MAX_PAGECACHE_ORDER, which is smaller than the PMD order on arm64 with 64K pages, where a PMD is 512M. A PMD-sized page cache folio is impossible there, so MADV_COLLAPSE answers -EINVAL and khugepaged passes over the range. The shmem cases ask for a PMD-sized folio anyway, so four of them fail and the run bails out in the middle.
MAX_PAGECACHE_ORDER is not shmem-specific: it caps every file folio. Skip both mem types where the cap is below the PMD order. Anonymous collapse is unaffected: its orders are not capped this way. Assisted-by: Claude-Code:claude-opus-5 Tested-by: Muhammad Usama Anjum <[email protected]> Signed-off-by: Kiryl Shutsemau (Meta) <[email protected]> --- tools/testing/selftests/mm/khugepaged.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c index c499804a0ec4..ec5c36a19d92 100644 --- a/tools/testing/selftests/mm/khugepaged.c +++ b/tools/testing/selftests/mm/khugepaged.c @@ -1357,6 +1357,30 @@ int main(int argc, char **argv) setbuf(stdout, NULL); + /* + * The page cache caps folio order at MAX_PAGECACHE_ORDER, which is + * below the PMD order on arm64 with 64K pages. A PMD-sized page cache + * folio is impossible there, so the kernel refuses these collapses by + * design and there is nothing to test. The cap is not shmem-specific: + * it rules out regular files too, and the per-order shmem_enabled + * controls exist for exactly the orders it allows, which is what makes + * them readable here. + */ + if (!(thp_shmem_supported_orders() & (1UL << hpage_pmd_order))) { + if (shmem_ops) { + ksft_print_msg("no PMD-order page cache folio: skipping shmem\n"); + shmem_ops = NULL; + } + if (read_only_file_ops) { + ksft_print_msg("no PMD-order page cache folio: skipping file\n"); + read_only_file_ops = NULL; + read_write_file_read_ops = NULL; + read_write_file_write_ops = NULL; + } + if (!anon_ops && !shmem_ops && !read_only_file_ops) + ksft_exit_skip("Nothing left to collapse into\n"); + } + default_settings.khugepaged.max_ptes_none = hpage_pmd_nr - 1; default_settings.khugepaged.max_ptes_swap = hpage_pmd_nr / 8; default_settings.khugepaged.max_ptes_shared = hpage_pmd_nr / 2; -- 2.54.0
