From: "Kiryl Shutsemau (Meta)" <[email protected]> An mTHP collapse test has to ask whether a range came out as folios of one particular order, placed where a collapse would place them. Nothing answers that today: is_backed_by_folio() classifies the folio behind a single page, and check_huge_anon() reads smaps AnonHugePages, which only accounts PMD mappings.
Add is_range_backed_by_folio_orders(). For every order-aligned window of the range it requires a present head PFN at its natural alignment and a contiguous PFN run across the window. A window stitched together from several folios, or one holding a folio shifted off its natural position, fails -- which is what makes the helper usable for "this window collapsed and that one did not". Assisted-by: Claude-Code:claude-opus-5 Signed-off-by: Kiryl Shutsemau (Meta) <[email protected]> --- tools/testing/selftests/mm/vm_util.c | 42 ++++++++++++++++++++++++++++ tools/testing/selftests/mm/vm_util.h | 2 ++ 2 files changed, 44 insertions(+) diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c index 3c276865a778..3f586f2c3d33 100644 --- a/tools/testing/selftests/mm/vm_util.c +++ b/tools/testing/selftests/mm/vm_util.c @@ -556,6 +556,48 @@ bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd, return false; } +/* + * Check whether every order-@order window of [start, len) maps exactly one + * folio of that order, head to tail. The address range must be naturally + * aligned, each window's PFN run must be contiguous, and a window's first + * PFN must be the folio head. + * + * This is the check "did this range collapse into order-@order folios": a + * window assembled from parts of several folios, or mapping a folio shifted + * from its natural position, fails. + */ +bool is_range_backed_by_folio_orders(char *start, size_t len, int order, + int pagemap_fd, int kpageflags_fd) +{ + const unsigned long nr_pages = 1UL << order; + const size_t window = nr_pages * psize(); + char *vaddr; + + if ((uintptr_t)start % window || len % window) + return false; + + for (vaddr = start; vaddr < start + len; vaddr += window) { + unsigned long pfn = pagemap_get_pfn(pagemap_fd, vaddr); + unsigned long i; + + /* Not present, or not mapping the folio head. */ + if (pfn == -1UL || pfn % nr_pages) + return false; + + for (i = 1; i < nr_pages; i++) { + if (pagemap_get_pfn(pagemap_fd, vaddr + i * psize()) != + pfn + i) + return false; + } + + if (!is_backed_by_folio(vaddr, order, pagemap_fd, + kpageflags_fd)) + return false; + } + + return true; +} + /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */ int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len, bool miss, bool wp, bool minor, uint64_t *ioctls) diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h index 56a28ce7d029..39dfb18dc10c 100644 --- a/tools/testing/selftests/mm/vm_util.h +++ b/tools/testing/selftests/mm/vm_util.h @@ -99,6 +99,8 @@ int gather_folio_orders(char *vaddr_start, size_t len, int pagemap_fd, int kpageflags_fd, int orders[], int nr_orders); bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd, int kpageflags_fd); +bool is_range_backed_by_folio_orders(char *start, size_t len, int order, + int pagemap_fd, int kpageflags_fd); int uffd_register(int uffd, void *addr, uint64_t len, bool miss, bool wp, bool minor); -- 2.54.0
