+ selftests-mm-split_huge_page_test-cleanups-for-split_pte_mapped_thp-test.patch added to mm-new branch

+ selftests-mm-split_huge_page_test-cleanups-for-split_pte_mapped_thp-test.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: selftests/mm: split_huge_page_test: cleanups for split_pte_mapped_thp test
has been added to the -mm mm-new branch.  Its filename is
     selftests-mm-split_huge_page_test-cleanups-for-split_pte_mapped_thp-test.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-mm-split_huge_page_test-cleanups-for-split_pte_mapped_thp-test.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: David Hildenbrand <david@redhat.com>
Subject: selftests/mm: split_huge_page_test: cleanups for split_pte_mapped_thp test
Date: Wed, 3 Sep 2025 09:02:53 +0200

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.

Link: https://lkml.kernel.org/r/20250903070253.34556-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/split_huge_page_test.c |  117 +++++++-----
 1 file changed, 71 insertions(+), 46 deletions(-)

--- a/tools/testing/selftests/mm/split_huge_page_test.c~selftests-mm-split_huge_page_test-cleanups-for-split_pte_mapped_thp-test
+++ a/tools/testing/selftests/mm/split_huge_page_test.c
@@ -389,67 +389,92 @@ static void split_pmd_thp_to_order(int o
 
 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));
-
-	madvise(one_page, len, MADV_HUGEPAGE);
-
-	for (i = 0; i < len; i++)
-		one_page[i] = (char)i;
+	if (thp_area == MAP_FAILED) {
+		ksft_test_result_fail("Fail to allocate memory: %s\n", strerror(errno));
+		return;
+	}
 
-	if (!check_huge_anon(one_page, 4, pmd_pagesize))
-		ksft_exit_fail_msg("No THP is allocated\n");
+	madvise(thp_area, thp_area_size, MADV_HUGEPAGE);
 
-	/* remap the first pagesize of first THP */
-	pte_mapped = mremap(one_page, pagesize, pagesize, MREMAP_MAYMOVE);
+	for (i = 0; i < thp_area_size; i++)
+		thp_area[i] = (char)i;
 
-	/* 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));
+	if (!check_huge_anon(thp_area, nr_thps, pmd_pagesize)) {
+		ksft_test_result_skip("Not all THPs allocated\n");
+		goto out;
 	}
 
-	/* 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");
+	/*
+	 * 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;
+	}
 
-	/* split all remapped THPs */
-	write_debugfs(PID_FMT, getpid(), (uint64_t)pte_mapped,
-		      (uint64_t)pte_mapped + pagesize * 4, 0);
+	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;
+	}
 
-	/* 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);
+	/*
+	 * 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 (i % pagesize == 0 &&
-		    !is_backed_by_folio(&pte_mapped[i], 0, pagemap_fd, kpageflags_fd))
-			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;
 	}
 
-	if (thp_size)
-		ksft_exit_fail_msg("Still %ld THPs not split\n", thp_size);
+	/* 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)
_

Patches currently in -mm which might be from david@redhat.com are

mm-migrate-remove-migratepage_unmap.patch
mm-migrate-remove-migratepage_unmap-fix.patch
treewide-remove-migratepage_success.patch
mm-huge_memory-move-more-common-code-into-insert_pmd.patch
mm-huge_memory-move-more-common-code-into-insert_pud.patch
mm-huge_memory-support-huge-zero-folio-in-vmf_insert_folio_pmd.patch
fs-dax-use-vmf_insert_folio_pmd-to-insert-the-huge-zero-folio.patch
mm-huge_memory-mark-pmd-mappings-of-the-huge-zero-folio-special.patch
powerpc-ptdump-rename-struct-pgtable_level-to-struct-ptdump_pglevel.patch
mm-rmap-convert-enum-rmap_level-to-enum-pgtable_level.patch
mm-memory-convert-print_bad_pte-to-print_bad_page_map.patch
mm-memory-convert-print_bad_pte-to-print_bad_page_map-fix.patch
mm-memory-factor-out-common-code-from-vm_normal_page_.patch
mm-introduce-and-use-vm_normal_page_pud.patch
mm-rename-vm_ops-find_special_page-to-vm_ops-find_normal_page.patch
prctl-extend-pr_set_thp_disable-to-optionally-exclude-vm_hugepage.patch
mm-huge_memory-convert-tva_flags-to-enum-tva_type.patch
mm-huge_memory-respect-madv_collapse-with-pr_thp_disable_except_advised.patch
mm-stop-making-sparsemem_vmemmap-user-selectable.patch
arm64-kconfig-drop-superfluous-select-sparsemem_vmemmap.patch
s390-kconfig-drop-superfluous-select-sparsemem_vmemmap.patch
x86-kconfig-drop-superfluous-select-sparsemem_vmemmap.patch
wireguard-selftests-remove-config_sparsemem_vmemmap=y-from-qemu-kernel-config.patch
mm-page_alloc-reject-unreasonable-folio-compound-page-sizes-in-alloc_contig_range_noprof.patch
mm-memremap-reject-unreasonable-folio-compound-page-sizes-in-memremap_pages.patch
mm-hugetlb-check-for-unreasonable-folio-sizes-when-registering-hstate.patch
mm-mm_init-make-memmap_init_compound-look-more-like-prep_compound_page.patch
mm-sanity-check-maximum-folio-size-in-folio_set_order.patch
mm-limit-folio-compound-page-sizes-in-problematic-kernel-configs.patch
mm-simplify-folio_page-and-folio_page_idx.patch
mm-hugetlb-cleanup-hugetlb_folio_init_tail_vmemmap.patch
mm-mm-percpu-km-drop-nth_page-usage-within-single-allocation.patch
fs-hugetlbfs-remove-nth_page-usage-within-folio-in-adjust_range_hwpoison.patch
fs-hugetlbfs-cleanup-folio-in-adjust_range_hwpoison.patch
mm-pagewalk-drop-nth_page-usage-within-folio-in-folio_walk_start.patch
mm-gup-drop-nth_page-usage-within-folio-when-recording-subpages.patch
mm-gup-remove-record_subpages.patch
io_uring-zcrx-remove-nth_page-usage-within-folio.patch
mips-mm-convert-__flush_dcache_pages-to-__flush_dcache_folio_pages.patch
mm-cma-refuse-handing-out-non-contiguous-page-ranges.patch
dma-remap-drop-nth_page-in-dma_common_contiguous_remap.patch
scatterlist-disallow-non-contigous-page-ranges-in-a-single-sg-entry.patch
ata-libata-sff-drop-nth_page-usage-within-sg-entry.patch
drm-i915-gem-drop-nth_page-usage-within-sg-entry.patch
mspro_block-drop-nth_page-usage-within-sg-entry.patch
memstick-drop-nth_page-usage-within-sg-entry.patch
mmc-drop-nth_page-usage-within-sg-entry.patch
scsi-scsi_lib-drop-nth_page-usage-within-sg-entry.patch
scsi-sg-drop-nth_page-usage-within-sg-entry.patch
vfio-pci-drop-nth_page-usage-within-sg-entry.patch
crypto-remove-nth_page-usage-within-sg-entry.patch
mm-gup-drop-nth_page-usage-in-unpin_user_page_range_dirty_lock.patch
kfence-drop-nth_page-usage.patch
block-update-comment-of-struct-bio_vec-regarding-nth_page.patch
mm-remove-nth_page.patch
selftests-mm-split_huge_page_test-fix-occasional-is_backed_by_folio-wrong-results.patch
selftests-mm-split_huge_page_test-cleanups-for-split_pte_mapped_thp-test.patch