> On 9/7/26 10:19, 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.
> >
> > Instead of relying on /proc/self/smaps, use /proc/self/pagemap and
> > /proc/kpageflags to detect huge-page mappings and large folios:
> >
> > 1. If hpage_size == pmd_pagesize, check PAGE_IS_HUGE instead of
> > using check_large_folios(), since only the mapping type matters.
> > This identifies PMD-mapped huge pages.
> > 2. Otherwise, use check_large_folios() to detect large folios. This
> > covers mTHP cases.
> > 3. Check the folio flags according to the type of huge page.
> >
> > Suggested-by: David Hildenbrand (Arm) <[email protected]>
> > Suggested-by: Zi Yan <[email protected]>
> > Reviewed-by: Zi Yan <[email protected]>
> > Reviewed-by: Baolin Wang <[email protected]>
> > Tested-by: Baolin Wang <[email protected]>
> > Acked-by: Lorenzo Stoakes (ARM) <[email protected]>
> > Signed-off-by: Yeoreum Yun <[email protected]>
> > ---
> > tools/testing/selftests/mm/vm_util.c | 145
> > ++++++++++++++++++++++-------------
> > tools/testing/selftests/mm/vm_util.h | 1 +
> > 2 files changed, 92 insertions(+), 54 deletions(-)
> >
> > diff --git a/tools/testing/selftests/mm/vm_util.c
> > b/tools/testing/selftests/mm/vm_util.c
> > index 4821a3563036..dc62ce84e143 100644
>
> [...]
>
> >
> > - if (hpage_size == pmd_pagesize)
> > - return __check_pmd_huge(addr, "AnonHugePages: ", nr_hpages,
> > hpage_size);
> > +static bool check_huge_type(uint64_t categories, uint64_t kpageflags,
> > + enum check_huge_type type)
> > +{
> > + const bool file = categories & PAGE_IS_FILE;
> > + const 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;
> > + }
>
> Why do we even need CHECK_HUGE_SHMEM?
>
> That's really just a legacy thing for using smaps to identify huge pages.
>
> It's sufficient to identify CHECK_HUGE_FILE if you know that you have shmem
> mapping.
>
> You will not arbitrarily have non-shmem folios in a shmem mapping :)
Agree. but there seems the case where discern whethr the mapping is
with regular file or shmem like tmpfs -- khugepaged test where using
__shmem_ops. So I think it would be better to keep this as-is.
>
> >
> > - return check_large_folios(addr, len, nr_hpages, hpage_size);
> > + return false;
> > }
> >
> > -bool check_huge_file(void *addr, size_t len, int nr_hpages, uint64_t
> > hpage_size)
> > +static bool __check_huge(void *addr, size_t len, int nr_hpages,
> > + uint64_t hpage_size, enum check_huge_type type)
> > {
> > - uint64_t pmd_pagesize = read_pmd_pagesize();
> > + bool ret = false;
> > + 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, allow_nonpresent;
> > + 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, "FilePmdMapped:", nr_hpages,
> > hpage_size);
> > + 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;
> >
> > - return check_large_folios(addr, len, nr_hpages, hpage_size);
> > + 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);
>
> No need to cleanup when exiting.
Yes, but some test code does clean it up, so I was just confused
about the convention :\
>
> > + ksft_exit_fail_msg("open kpageflags fail\n");
> > + }
> > +
> > + 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;
> > + else
> > + 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;
> > + ret = true;
> > +
> > +out:
> > + close(pagemap_fd);
> > + close(kpageflags_fd);
> > + return ret;
> > }
>
>
>
> --
> Cheers,
>
> David
>
--
Sincerely,
Yeoreum Yun
