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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/2/25 9:55 PM, David Hildenbrand wrote: > 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 > Signed-off-by: David Hildenbrand > --- > .../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); > } > > I have tested this patch on a system with a 64 KB page size, and all tests passed. # Totals: pass:34 fail:0 xfail:0 xpass:0 skip:0 error:0 Tested by: Donet Tom > > > > > static void split_file_backed_thp(int order) --------------BoRxvhG5r54WLqmtSDTOR9DW Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 7bit


On 9/2/25 9:55 PM, David Hildenbrand wrote:
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@nvidia.com>
Signed-off-by: David Hildenbrand <david@redhat.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);
 }

I have tested this patch on a system with a 64 KB page size, and all tests passed.

# Totals: pass:34 fail:0 xfail:0 xpass:0 skip:0 error:0

Tested by: Donet Tom <donettom@linux.ibm.com> 




 
 static void split_file_backed_thp(int order)
--------------BoRxvhG5r54WLqmtSDTOR9DW--