Re: [PATCH v5 2/3] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper
From: "David Hildenbrand (Arm)" <david@kernel.org>
Date: 2026-09-10 10:21:04
Also in:
linux-kselftest, lkml
On 9/7/26 10:19, Yeoreum Yun wrote:
quoted hunk ↗ jump to hunk
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) <david@kernel.org> Suggested-by: Zi Yan <ziy@nvidia.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com> Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org> Signed-off-by: Yeoreum Yun <redacted> --- 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 :)
- 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.
+ 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