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Message-ID: <20250903070253.34556-3-david@redhat.com>
Date: Wed, 3 Sep 2025 09:02:53 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
linux-kselftest@...r.kernel.org,
David Hildenbrand <david@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
Zi Yan <ziy@...dia.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
Nico Pache <npache@...hat.com>,
Ryan Roberts <ryan.roberts@....com>,
Dev Jain <dev.jain@....com>,
Barry Song <baohua@...nel.org>,
Wei Yang <richard.weiyang@...il.com>
Subject: [PATCH v2 2/2] selftests/mm: split_huge_page_test: cleanups for split_pte_mapped_thp test
There is room for improvement, so let's clean up a bit:
(1) Define "4" as a constant.
(2) SKIP if we fail to allocate all THPs (e.g., fragmented) and add
recovery code for all other failure cases: no need to exit the test.
(3) Rename "len" to thp_area_size, and "one_page" to "thp_area".
(4) Allocate a new area "page_area" into which we will mremap the
pages; add "page_area_size". Now we can easily merge the two
mremap instances into a single one.
(5) Iterate THPs instead of bytes when checking for missed THPs after
mremap.
(6) Rename "pte_mapped2" to "tmp", used to verify mremap(MAP_FIXED)
result.
(7) Split the corruption test from the failed-split test, so we can just
iterate bytes vs. thps naturally.
(8) Extend comments and clarify why we are using mremap in the first
place.
Reviewed-by: Zi Yan <ziy@...dia.com>
Reviewed-by: Wei Yang <richard.weiyang@...il.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
.../selftests/mm/split_huge_page_test.c | 123 +++++++++++-------
1 file changed, 74 insertions(+), 49 deletions(-)
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 72d6d8bb329ed..7731191cc8e9b 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -389,67 +389,92 @@ 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, *tmp, *page_area = MAP_FAILED;
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));
+ 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 a single page of each
+ * THP (page[i] of thp[i]) in the thp_area into page_area. This will
+ * replace the PMD mappings in the thp_area by PTE mappings first,
+ * but leaving the THP unsplit, to then create a page-sized hole in
+ * the thp_area.
+ * We will then manually trigger splitting of all THPs through the
+ * single mremap'ed pages of each THP in the page_area.
+ */
+ 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 * pagesize, 0,
+ pagemap_fd, kpageflags_fd))
+ 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 != MAP_FAILED)
+ munmap(page_area, page_area_size);
}
static void split_file_backed_thp(int order)
--
2.50.1
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