> > > On 8/28/26 12:54 AM, Yeoreum Yun wrote: > > On Thu, Aug 27, 2026 at 11:03:17AM -0400, Zi Yan wrote: > > > On Thu Aug 27, 2026 at 6:44 AM EDT, Yeoreum Yun wrote: > > > > Hi Baolin, > > > > > > > > > > > > > > > > > > > On 8/26/26 8:24 PM, Yeoreum Yun wrote: > > > > > > Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default > > > > > > on AArch64”), > > > > > > glibc may call madvise(MADV_HUGEPAGE) for sufficiently large > > > > > > allocations > > > > > > made by memalign(). > > > > > > > > > > > > The underlying VMA may start at a different address from the aligned > > > > > > address returned by memalign(). Furthermore, a subsequent > > > > > > madvise(MADV_HUGEPAGE) call does not split the VMA because the flag > > > > > > is > > > > > > already set. > > > > > > > > > > > > This causes split_huge_page_test to fail because the > > > > > > check_huge_xxx() > > > > > > helpers incorrectly require the address returned by memalign() to > > > > > > match the VMA start address reported in /proc/self/smaps. > > > > > > > > > > > > Fix this by using /proc/self/pagemap and /proc/kpageflags instead of > > > > > > /proc/self/smaps to detect huge pages. > > > > > > > > > > > > Reported-by: David Hildenbrand (Arm) <[email protected]> > > > > > > Signed-off-by: Yeoreum Yun <[email protected]> > > > > > > --- > > > > > > tools/testing/selftests/mm/vm_util.c | 130 > > > > > > ++++++++++++++++++++--------------- > > > > > > tools/testing/selftests/mm/vm_util.h | 1 + > > > > > > 2 files changed, 77 insertions(+), 54 deletions(-) > > > > > > > > > > > > diff --git a/tools/testing/selftests/mm/vm_util.c > > > > > > b/tools/testing/selftests/mm/vm_util.c > > > > > > index 4821a3563036..1d0959b3b9e8 100644 > > > > > > --- a/tools/testing/selftests/mm/vm_util.c > > > > > > +++ b/tools/testing/selftests/mm/vm_util.c > > > > > > @@ -351,31 +351,13 @@ char *__get_smap_entry(void *addr, const char > > > > > > *pattern, char *buf, size_t len) > > > > > > return entry; > > > > > > } > > > > > > -static bool __check_pmd_huge(void *addr, char *pattern, int > > > > > > nr_hpages, > > > > > > - uint64_t hpage_size) > > > > > > -{ > > > > > > - char buffer[MAX_LINE_LENGTH]; > > > > > > - uint64_t thp = -1; > > > > > > - char *entry; > > > > > > - > > > > > > - entry = __get_smap_entry(addr, pattern, buffer, sizeof(buffer)); > > > > > > - if (!entry) > > > > > > - goto err_out; > > > > > > - > > > > > > - if (sscanf(entry, "%9" SCNu64 " kB", &thp) != 1) > > > > > > - ksft_exit_fail_msg("Reading smap error\n"); > > > > > > - > > > > > > -err_out: > > > > > > - return thp == (nr_hpages * (hpage_size >> 10)); > > > > > > -} > > > > > > - > > > > > > -static bool check_large_folios(void *addr, size_t len, int > > > > > > nr_hpages, > > > > > > - uint64_t hpage_size) > > > > > > +static bool check_large_folios(int pagemap_fd, int kpageflags_fd, > > > > > > + void *addr, size_t len, int nr_hpages, > > > > > > + uint64_t hpage_size) > > > > > > { > > > > > > int order = 0, pagesize = getpagesize(); > > > > > > unsigned int nr_pages = hpage_size / pagesize; > > > > > > int orders[MAX_NR_ORDERS], status; > > > > > > - int pagemap_fd, kpageflags_fd; > > > > > > bool ret = false; > > > > > > if (!nr_pages) > > > > > > @@ -386,15 +368,6 @@ static bool check_large_folios(void *addr, > > > > > > size_t len, int nr_hpages, > > > > > > ksft_exit_fail_msg("invalid order\n"); > > > > > > memset(orders, 0, sizeof(int) * MAX_NR_ORDERS); > > > > > > - pagemap_fd = open(PAGEMAP_PATH, O_RDONLY); > > > > > > - if (pagemap_fd == -1) > > > > > > - ksft_exit_fail_msg("read pagemap fail\n"); > > > > > > - > > > > > > - kpageflags_fd = open(KPAGEFLAGS_PATH, O_RDONLY); > > > > > > - if (kpageflags_fd == -1) { > > > > > > - close(pagemap_fd); > > > > > > - ksft_exit_fail_msg("read kpageflags fail\n"); > > > > > > - } > > > > > > status = gather_folio_orders(addr, len, pagemap_fd, > > > > > > kpageflags_fd, orders, MAX_NR_ORDERS); > > > > > > @@ -405,48 +378,97 @@ static bool check_large_folios(void *addr, > > > > > > size_t len, int nr_hpages, > > > > > > ret = true; > > > > > > out: > > > > > > - close(pagemap_fd); > > > > > > - close(kpageflags_fd); > > > > > > return ret; > > > > > > } > > > > > > -bool check_huge_anon(void *addr, size_t len, int nr_hpages, > > > > > > uint64_t hpage_size) > > > > > > +enum check_huge_type { > > > > > > + CHECK_HUGE_ANON, > > > > > > + CHECK_HUGE_FILE, > > > > > > + CHECK_HUGE_SHMEM, > > > > > > +}; > > > > > > + > > > > > > +static bool __check_pmd_huge(void *addr, size_t len, int nr_hpages, > > > > > > + uint64_t hpage_size, enum check_huge_type > > > > > > type) > > > > > > > > > > The original __check_pmd_huge() is only for PMD-sized large folios, > > > > > but now > > > > > it not only checks PMD-sized large folios but also mTHP large folios, > > > > > which > > > > > I find confusing. Please keep its original semantics, and only check > > > > > PMD-sized large folios. > > > > > > > > But, It seems to valuable to check other page-flags than checking > > > > the large-folio only. > > > > > > > > > > > > > > > { > > > > > > - uint64_t pmd_pagesize = read_pmd_pagesize(); > > > > > > + int pagemap_fd, kpageflags_fd; > > > > > > + uint64_t pmd_pagesize, granule; > > > > > > + uint64_t categories, kpf; > > > > > > + unsigned long pfn; > > > > > > + bool check_large, huge_mapped; > > > > > > + char *start = addr; > > > > > > + char *end = start + len; > > > > > > + pmd_pagesize = read_pmd_pagesize(); > > > > > > if (!pmd_pagesize) > > > > > > ksft_exit_fail_msg("reading PMD pagesize failed\n"); > > > > > > - if (hpage_size == pmd_pagesize) > > > > > > - return __check_pmd_huge(addr, "AnonHugePages: ", > > > > > > nr_hpages, hpage_size); > > > > > > + if (nr_hpages > 0) { > > > > > > + check_large = true; > > > > > > + granule = hpage_size; > > > > > > + } else { > > > > > > + check_large = false; > > > > > > + granule = psize(); > > > > > > + } > > > > > > > > > > This is incorrect for the mTHP large folio check. I already hit a > > > > > selftest > > > > > failure. Please test your patches before sending them out. > > > > > > > > Since for a split case, large folio can be as-is but only remove > > > > the PMD mapping only, skipping the large_folio checking seems valid > > > > when nr_hpage is 0. > > > > > > What split care are you referring to? split_huge_page_test() always > > > splits the folio. > > > > Not for split_huge_page_test case but for khugepage testcase like > > collapse_full_of_compound() test. > > > > > > > > > > > > > And the failure of test seems because of unmapped area after > > > > changinng the collapse-order. Therefore, it seems to fine with below > > > > patch: > > > > > > > > ---------------&<---------------------- > > > > > > > > diff --git a/tools/testing/selftests/mm/vm_util.c > > > > b/tools/testing/selftests/mm/vm_util.c > > > > index 1d0959b3b9e8..f174a76d2310 100644 > > > > --- a/tools/testing/selftests/mm/vm_util.c > > > > +++ b/tools/testing/selftests/mm/vm_util.c > > > > @@ -387,14 +387,14 @@ enum check_huge_type { > > > > CHECK_HUGE_SHMEM, > > > > }; > > > > > > > > -static bool __check_pmd_huge(void *addr, size_t len, int nr_hpages, > > > > - uint64_t hpage_size, enum check_huge_type > > > > type) > > > > +static bool __check_huge(void *addr, size_t len, int nr_hpages, > > > > + uint64_t hpage_size, enum check_huge_type type) > > > > { > > > > int pagemap_fd, kpageflags_fd; > > > > uint64_t pmd_pagesize, granule; > > > > uint64_t categories, kpf; > > > > unsigned long pfn; > > > > - bool check_large, huge_mapped; > > > > + bool check_large, check_huge_mapped, allow_nomap; > > > > char *start = addr; > > > > char *end = start + len; > > > > > > > > @@ -405,11 +405,20 @@ static bool __check_pmd_huge(void *addr, size_t > > > > len, int nr_hpages, > > > > if (nr_hpages > 0) { > > > > check_large = true; > > > > granule = hpage_size; > > > > + if (granule == pmd_pagesize) > > > > + check_huge_mapped = true; > > > > + else > > > > + check_huge_mapped = false; > > > > } else { > > > > check_large = false; > > > > granule = psize(); > > > > } > > > > > > The else is for nr_hpages == 0? But it looks like we allow negative > > > nr_hpages. Maybe add a bool expect_huge = nr_hpages > 0 to make it > > > explicit. > > > > Fair enough. I'll change. > > > > > > > > granule is an optimization for PAGE_IS_HUGE scanning? When we expect a > > > PMD mapping, we just scan at pmd_pagesize granularity, otherwise we > > > check every single page? > > > > > > At the high level, the function looks good to me, the rules are: > > > > > > 1. if hpage_size == pmd_pagesize, we need to check PAGE_IS_HUGE and > > > check_large_folio() can be skipped, since we only care about mappings. > > > This checks for PMD mappings. > > > > > > 2. in other cases, check_large_folios() is always needed. This is for > > > mTHP checks. > > Yes, this is also what I thought. And the following code looks good to me. > Thanks. > > > Exactly, but for some testcase where use this function, doesn't > > trigger split of large _folio but only check the HUGE MAP is removed > > (nr_hpage == 0), it skips the chekc_large_folio(). > > > > > > > > I think the ifs at the beginning is confusing. Can we do something like > > > below to get rid of the ifs? I also moved KPF_* checks in a separate > > > function. Feel free to make changes if you find any issue there. > > > > > > static bool check_huge_type(uint64_t categories, uint64_t kpageflags, > > > enum check_huge_type type) > > > { > > > bool file = categories & PAGE_IS_FILE; > > > bool swapbacked = kpageflags & KPF_SWAPBACKED; > > > > > > switch (type) { > > > case CHECK_HUGE_ANON: > > > return !file; > > > case CHECK_HUGE_FILE: > > > return file && !swapbacked; > > > case CHECK_HUGE_SHMEM: > > > return file && swapbacked; > > > } > > > > > > return false; > > > } > > > > > > static bool __check_huge(void *addr, size_t len, int nr_hpages, > > > uint64_t hpage_size, enum check_huge_type type) > > > { > > > int pagemap_fd, kpageflags_fd; > > > int nr_pmd_mappings = 0; > > > uint64_t pmd_pagesize, scan_mapping_size; > > > uint64_t categories, kpf; > > > unsigned long pfn; > > > bool check_pmd_mapping; > > > bool allow_nonpresent; > > > bool ret = false; > > > char *start = addr; > > > char *end = start + len; > > > > > > pmd_pagesize = read_pmd_pagesize(); > > > if (!pmd_pagesize) > > > ksft_exit_fail_msg("reading PMD pagesize failed\n"); > > > > > > check_pmd_mapping = hpage_size == pmd_pagesize; > > > scan_mapping_size = nr_hpages > 0 ? hpage_size : psize(); > > > /* Some mTHP tests check a partially populated PMD-sized range. */ > > > allow_nonpresent = (uint64_t)nr_hpages * hpage_size < len; > > > > > > pagemap_fd = open(PAGEMAP_PATH, O_RDONLY); > > > if (pagemap_fd < 0) > > > ksft_exit_fail_msg("open pagemap fail\n"); > > > > > > kpageflags_fd = open(KPAGEFLAGS_PATH, O_RDONLY); > > > if (kpageflags_fd < 0) { > > > close(pagemap_fd); > > > ksft_exit_fail_msg("open kpageflags fail\n"); > > > } > > > > > > /* PTE-mapped large folios cannot be identified by PAGE_IS_HUGE. */ > > > if (!check_pmd_mapping && > > > !check_large_folios(pagemap_fd, kpageflags_fd, addr, len, > > > nr_hpages, hpage_size)) > > > goto out; > > > > > > for (; start < end; start += scan_mapping_size) { > > > categories = pagemap_scan_get_categories(pagemap_fd, start); > > > pfn = pagemap_get_pfn(pagemap_fd, start); > > > if (pfn == -1UL) { > > > if (!allow_nonpresent) > > > goto out; > > > continue; > > > } > > > if (pageflags_get(pfn, kpageflags_fd, &kpf)) > > > ksft_exit_fail_msg("read kpageflags: %s\n", > > > strerror(errno)); > > > if (check_pmd_mapping && (categories & PAGE_IS_HUGE)) > > > nr_pmd_mappings++; > > > if (kpf & KPF_COMPOUND_TAIL) > > > continue; > > > if (!check_huge_type(categories, kpf, type)) > > > goto out; > > > } > > > if (check_pmd_mapping && nr_pmd_mappings != nr_hpages) > > > goto out; > > > > Again, because of collapse_full_of_compound() testcase, > > it would be failed for this. so, it would better to skip > > check_large_folioes() when nr_hpages is 0. > > IIUC, when nr_hpages is 0, we should also call check_large_folios() to > verify that there are no large folios within this address range, which is > also what the previous code did. > > Also, I tried Zi's code, and it passed all my khugepaged selftests. I'm not > sure why you saw the collapse_full_of_compound() test case fail.
Ah, Sorry to my misunderstding I've misread the code on condition :(. (!check_pmd_mapping as check_pmd_mapping)... Yeap. it seems fine to check PAGE_IS_HUGE instead of large folio for pmd_hugepage case. Sorry to make noise. -- Sincerely, Yeoreum Yun
