[PATCH v8 2/4] kselftest: mm: replace usage of /proc/self/smaps for __check_pmd_huge()

[Yeoreum Yun]

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_pmd_huge()
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 checking PAGE_IS_HUGE
and PAGE_IS_FILE accroding to type of huge page.

Since shmem pages are also file-backed, simply check whether the page
is file-backed.

Fixes: 642bc52aed9 ("selftests: vm: bring common functions to a new file")
Suggested-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
Signed-off-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
---
 tools/testing/selftests/mm/vm_util.c | 78 ++++++++++++++++++++++--------------
 1 file changed, 49 insertions(+), 29 deletions(-)

diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index a0ab78ceedb1..969d7202500c 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -351,24 +351,6 @@ char *__get_smap_entry(void *addr, const char *pattern, char *buf, size_t len)
 	return entry;
 }
 
-static bool __check_pmd_huge(void *addr, char *pattern, int nr_hpages,
-		  uint64_t hpage_size)
-{
-	char buffer[MAX_LINE_LENGTH];
-	uint64_t thp = -1;
-	char *entry;
-
-	entry = __get_smap_entry(addr, pattern, buffer, sizeof(buffer));
-	if (!entry)
-		goto err_out;
-
-	if (sscanf(entry, "%9" SCNu64 " kB", &thp) != 1)
-		ksft_exit_fail_msg("Reading smap error\n");
-
-err_out:
-	return thp == (nr_hpages * (hpage_size >> 10));
-}
-
 static bool check_large_folios(void *addr, size_t len, int nr_hpages,
 		uint64_t hpage_size)
 {
@@ -410,20 +392,51 @@ static bool check_large_folios(void *addr, size_t len, int nr_hpages,
 	return ret;
 }
 
-bool check_huge_anon(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
+enum check_huge_type {
+	CHECK_HUGE_ANON,
+	CHECK_HUGE_FILE,
+};
+
+static bool check_huge_type(uint64_t categories, enum check_huge_type type)
 {
-	uint64_t pmd_pagesize = read_pmd_pagesize();
+	const bool file = categories & PAGE_IS_FILE;
 
-	if (!pmd_pagesize)
-		ksft_exit_fail_msg("reading PMD pagesize failed\n");
+	switch (type) {
+	case CHECK_HUGE_ANON:
+		return !file;
+	case CHECK_HUGE_FILE:
+		return file;
+	}
 
-	if (hpage_size == pmd_pagesize)
-		return __check_pmd_huge(addr, "AnonHugePages: ", nr_hpages, hpage_size);
+	return false;
+}
 
-	return check_large_folios(addr, len, nr_hpages, hpage_size);
+static bool __check_pmd_huge(void *addr, size_t len, int nr_hpages,
+		  uint64_t hpage_size, enum check_huge_type type)
+{
+	int pagemap_fd;
+	int nr_pmd_mappings = 0;
+	uint64_t categories;
+	char *start = addr;
+	char *end = start + len;
+
+	pagemap_fd = open(PAGEMAP_PATH, O_RDONLY);
+	if (pagemap_fd < 0)
+		ksft_exit_fail_msg("open pagemap fail\n");
+
+	for (; start < end; start += hpage_size) {
+		categories = pagemap_scan_get_categories(pagemap_fd, start);
+		if (!(categories & PAGE_IS_HUGE))
+			continue;
+		if (check_huge_type(categories, type))
+			nr_pmd_mappings++;
+	}
+	close(pagemap_fd);
+
+	return nr_hpages == nr_pmd_mappings;
 }
 
-bool check_huge_file(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
+bool check_huge_anon(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
 {
 	uint64_t pmd_pagesize = read_pmd_pagesize();
 
@@ -431,12 +444,13 @@ bool check_huge_file(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
 		ksft_exit_fail_msg("reading PMD pagesize failed\n");
 
 	if (hpage_size == pmd_pagesize)
-		return __check_pmd_huge(addr, "FilePmdMapped:", nr_hpages, hpage_size);
+		return __check_pmd_huge(addr, len, nr_hpages, hpage_size,
+					CHECK_HUGE_ANON);
 
 	return check_large_folios(addr, len, nr_hpages, hpage_size);
 }
 
-bool check_huge_shmem(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
+bool check_huge_file(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
 {
 	uint64_t pmd_pagesize = read_pmd_pagesize();
 
@@ -444,11 +458,17 @@ bool check_huge_shmem(void *addr, size_t len, int nr_hpages, uint64_t hpage_size
 		ksft_exit_fail_msg("reading PMD pagesize failed\n");
 
 	if (hpage_size == pmd_pagesize)
-		return __check_pmd_huge(addr, "ShmemPmdMapped:", nr_hpages, hpage_size);
+		return __check_pmd_huge(addr, len, nr_hpages, hpage_size,
+					CHECK_HUGE_FILE);
 
 	return check_large_folios(addr, len, nr_hpages, hpage_size);
 }
 
+bool check_huge_shmem(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
+{
+	return check_huge_file(addr, len, nr_hpages, hpage_size);
+}
+
 int64_t allocate_transhuge(void *ptr, int pagemap_fd)
 {
 	uint64_t ent[2];

-- 
2.43.0