On 2 Sep 2025, at 11:28, David Hildenbrand wrote:
> [...]
>
>>> @@ -390,67 +390,88 @@ static void split_pmd_thp_to_order(int order)
>>> static void split_pte_mapped_thp(void)
>>> {
>>> - char *one_page, *pte_mapped, *pte_mapped2;
>>> - size_t len = 4 * pmd_pagesize;
>>> - uint64_t thp_size;
>>> + const size_t nr_thps = 4;
>>> + const size_t thp_area_size = nr_thps * pmd_pagesize;
>>> + const size_t page_area_size = nr_thps * pagesize;
>>> + char *thp_area, *page_area = NULL, *tmp;
>>> size_t i;
>>> - one_page = mmap((void *)(1UL << 30), len, PROT_READ | PROT_WRITE,
>>> + thp_area = mmap((void *)(1UL << 30), thp_area_size, PROT_READ |
>>> PROT_WRITE,
>>> MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
>>> - if (one_page == MAP_FAILED)
>>> - ksft_exit_fail_msg("Fail to allocate memory: %s\n",
>>> strerror(errno));
>>> + if (thp_area == MAP_FAILED) {
>>> + ksft_test_result_fail("Fail to allocate memory: %s\n",
>>> strerror(errno));
>>> + goto out;
>>
>> thp_area mmap failed and out label will try to munmap MAP_FAILED, which is
>> (void *) -1. munmap will fail with -EINVAL.
>
> Indeed, should just be a "return;"
>
>>
>>> + }
>>> - madvise(one_page, len, MADV_HUGEPAGE);
>>> + madvise(thp_area, thp_area_size, MADV_HUGEPAGE);
>>> - for (i = 0; i < len; i++)
>>> - one_page[i] = (char)i;
>>> + for (i = 0; i < thp_area_size; i++)
>>> + thp_area[i] = (char)i;
>>> - if (!check_huge_anon(one_page, 4, pmd_pagesize))
>>> - ksft_exit_fail_msg("No THP is allocated\n");
>>> + if (!check_huge_anon(thp_area, nr_thps, pmd_pagesize)) {
>>> + ksft_test_result_skip("Not all THPs allocated\n");
>>> + goto out;
>>> + }
>>> - /* remap the first pagesize of first THP */
>>> - pte_mapped = mremap(one_page, pagesize, pagesize, MREMAP_MAYMOVE);
>>> -
>>> - /* remap the Nth pagesize of Nth THP */
>>> - for (i = 1; i < 4; i++) {
>>> - pte_mapped2 = mremap(one_page + pmd_pagesize * i + pagesize * i,
>>> - pagesize, pagesize,
>>> - MREMAP_MAYMOVE|MREMAP_FIXED,
>>> - pte_mapped + pagesize * i);
>>> - if (pte_mapped2 == MAP_FAILED)
>>> - ksft_exit_fail_msg("mremap failed: %s\n",
>>> strerror(errno));
>>> - }
>>> -
>>> - /* smap does not show THPs after mremap, use kpageflags instead */
>>> - thp_size = 0;
>>> - for (i = 0; i < pagesize * 4; i++)
>>> - if (i % pagesize == 0 &&
>>> - is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd,
>>> kpageflags_fd))
>>> - thp_size++;
>>> -
>>> - if (thp_size != 4)
>>> - ksft_exit_fail_msg("Some THPs are missing during mremap\n");
>>> -
>>> - /* split all remapped THPs */
>>> - write_debugfs(PID_FMT, getpid(), (uint64_t)pte_mapped,
>>> - (uint64_t)pte_mapped + pagesize * 4, 0);
>>> -
>>> - /* smap does not show THPs after mremap, use kpageflags instead */
>>> - thp_size = 0;
>>> - for (i = 0; i < pagesize * 4; i++) {
>>> - if (pte_mapped[i] != (char)i)
>>> - ksft_exit_fail_msg("%ld byte corrupted\n", i);
>>> + /*
>>> + * To challenge spitting code, we will mremap page[x] of the
>>> + * thp[x] into a smaller area, and trigger the split from that
>>> + * smaller area. This will end up replacing the PMD mappings in
>>> + * the thp_area by PTE mappings first, leaving the THPs unsplit.
>>> + */
>>> + page_area = mmap(NULL, page_area_size, PROT_READ | PROT_WRITE,
>>> + MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
>>> + if (page_area == MAP_FAILED) {
>>> + ksft_test_result_fail("Fail to allocate memory: %s\n",
>>> strerror(errno));
>>> + goto out;
>>> + }
>>> - if (i % pagesize == 0 &&
>>> - !is_backed_by_folio(&pte_mapped[i], 0, pagemap_fd,
>>> kpageflags_fd))
>>> - thp_size++;
>>> + for (i = 0; i < nr_thps; i++) {
>>> + tmp = mremap(thp_area + pmd_pagesize * i + pagesize * i,
>>> + pagesize, pagesize, MREMAP_MAYMOVE|MREMAP_FIXED,
>>> + page_area + pagesize * i);
>>> + if (tmp != MAP_FAILED)
>>> + continue;
>>> + ksft_test_result_fail("mremap failed: %s\n", strerror(errno));
>>> + goto out;
>>> + }
>>> +
>>> + /*
>>> + * Verify that our THPs were not split yet. Note that
>>> + * check_huge_anon() cannot be used as it checks for PMD mappings.
>>> + */
>>> + for (i = 0; i < nr_thps; i++) {
>>> + if (is_backed_by_folio(page_area + i * pagesize, pmd_order,
>>> + pagemap_fd, kpageflags_fd))
>>> + continue;
>>> + ksft_test_result_fail("THP %zu missing after mremap\n", i);
>>> + goto out;
>>> }
>>> - if (thp_size)
>>> - ksft_exit_fail_msg("Still %ld THPs not split\n", thp_size);
>>> + /* Split all THPs through the remapped pages. */
>>> + write_debugfs(PID_FMT, getpid(), (uint64_t)page_area,
>>> + (uint64_t)page_area + page_area_size, 0);
>>> +
>>> + /* Corruption during mremap or split? */
>>> + for (i = 0; i < page_area_size; i++) {
>>> + if (page_area[i] == (char)i)
>>> + continue;
>>> + ksft_test_result_fail("%zu byte corrupted\n", i);
>>> + goto out;
>>> + }
>>> +
>>> + /* Split failed? */
>>> + for (i = 0; i < nr_thps; i++) {
>>> + if (is_backed_by_folio(&page_area[i], 0, pagemap_fd,
>>> kpageflags_fd))
>>
>> page_area + i * pagesize, like Wei pointed out in another email.
>>
>>> + continue;
>>> + ksft_test_result_fail("THP %zu not split\n", i);
>>> + }
>>> ksft_test_result_pass("Split PTE-mapped huge pages successful\n");
>>> - munmap(one_page, len);
>>> +out:
>>> + munmap(thp_area, thp_area_size);
>>> + if (page_area)
>>> + munmap(page_area, page_area_size);
>>> }
>>> static void split_file_backed_thp(int order)
>>> --
>>> 2.50.1
>>
>> Otherwise, LGTM. With all the changes in this email and other email,
>> feel free to add Reviewed-by: Zi Yan <[email protected]> when you send it
>> out formally.
>
> Thanks!
>
> I'm currently chasing why I keep getting temporary
>
> Bail out! Some THPs are missing during mremap
>
> Already on the old test. Something doesn't work quite right as it seems.
Did you also see “Failed to get folio info”?
If pageflags_get() cannot read kpageflags content, is_backed_by_folio()
would not be able to detect a THP.
Best Regards,
Yan, Zi
