Re: [PATCH v2 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper
From: Baolin Wang
Date: Thu Aug 27 2026 - 21:00:41 EST
On 8/28/26 12:54 AM, Yeoreum Yun wrote:
On Thu, Aug 27, 2026 at 11:03:17AM -0400, Zi Yan wrote:
On Thu Aug 27, 2026 at 6:44 AM EDT, Yeoreum Yun wrote:
Hi Baolin,
On 8/26/26 8:24 PM, Yeoreum Yun wrote:
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_huge_xxx()
helpers incorrectly require the address returned by memalign() to
match the VMA start address reported in /proc/self/smaps.
Fix this by using /proc/self/pagemap and /proc/kpageflags instead of
/proc/self/smaps to detect huge pages.
Reported-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
Signed-off-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
---
tools/testing/selftests/mm/vm_util.c | 130 ++++++++++++++++++++---------------
tools/testing/selftests/mm/vm_util.h | 1 +
2 files changed, 77 insertions(+), 54 deletions(-)
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 4821a3563036..1d0959b3b9e8 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -351,31 +351,13 @@ 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)
+static bool check_large_folios(int pagemap_fd, int kpageflags_fd,
+ void *addr, size_t len, int nr_hpages,
+ uint64_t hpage_size)
{
int order = 0, pagesize = getpagesize();
unsigned int nr_pages = hpage_size / pagesize;
int orders[MAX_NR_ORDERS], status;
- int pagemap_fd, kpageflags_fd;
bool ret = false;
if (!nr_pages)
@@ -386,15 +368,6 @@ static bool check_large_folios(void *addr, size_t len, int nr_hpages,
ksft_exit_fail_msg("invalid order\n");
memset(orders, 0, sizeof(int) * MAX_NR_ORDERS);
- pagemap_fd = open(PAGEMAP_PATH, O_RDONLY);
- if (pagemap_fd == -1)
- ksft_exit_fail_msg("read pagemap fail\n");
-
- kpageflags_fd = open(KPAGEFLAGS_PATH, O_RDONLY);
- if (kpageflags_fd == -1) {
- close(pagemap_fd);
- ksft_exit_fail_msg("read kpageflags fail\n");
- }
status = gather_folio_orders(addr, len, pagemap_fd,
kpageflags_fd, orders, MAX_NR_ORDERS);
@@ -405,48 +378,97 @@ static bool check_large_folios(void *addr, size_t len, int nr_hpages,
ret = true;
out:
- close(pagemap_fd);
- close(kpageflags_fd);
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,
+ CHECK_HUGE_SHMEM,
+};
+
+static bool __check_pmd_huge(void *addr, size_t len, int nr_hpages,
+ uint64_t hpage_size, enum check_huge_type type)
The original __check_pmd_huge() is only for PMD-sized large folios, but now
it not only checks PMD-sized large folios but also mTHP large folios, which
I find confusing. Please keep its original semantics, and only check
PMD-sized large folios.
But, It seems to valuable to check other page-flags than checking
the large-folio only.
{
- uint64_t pmd_pagesize = read_pmd_pagesize();
+ int pagemap_fd, kpageflags_fd;
+ uint64_t pmd_pagesize, granule;
+ uint64_t categories, kpf;
+ unsigned long pfn;
+ bool check_large, huge_mapped;
+ char *start = addr;
+ char *end = start + len;
+ pmd_pagesize = read_pmd_pagesize();
if (!pmd_pagesize)
ksft_exit_fail_msg("reading PMD pagesize failed\n");
- if (hpage_size == pmd_pagesize)
- return __check_pmd_huge(addr, "AnonHugePages: ", nr_hpages, hpage_size);
+ if (nr_hpages > 0) {
+ check_large = true;
+ granule = hpage_size;
+ } else {
+ check_large = false;
+ granule = psize();
+ }
This is incorrect for the mTHP large folio check. I already hit a selftest
failure. Please test your patches before sending them out.
Since for a split case, large folio can be as-is but only remove
the PMD mapping only, skipping the large_folio checking seems valid
when nr_hpage is 0.
What split care are you referring to? split_huge_page_test() always
splits the folio.
Not for split_huge_page_test case but for khugepage testcase like
collapse_full_of_compound() test.
And the failure of test seems because of unmapped area after
changinng the collapse-order. Therefore, it seems to fine with below
patch:
---------------&<----------------------
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 1d0959b3b9e8..f174a76d2310 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -387,14 +387,14 @@ enum check_huge_type {
CHECK_HUGE_SHMEM,
};
-static bool __check_pmd_huge(void *addr, size_t len, int nr_hpages,
- uint64_t hpage_size, enum check_huge_type type)
+static bool __check_huge(void *addr, size_t len, int nr_hpages,
+ uint64_t hpage_size, enum check_huge_type type)
{
int pagemap_fd, kpageflags_fd;
uint64_t pmd_pagesize, granule;
uint64_t categories, kpf;
unsigned long pfn;
- bool check_large, huge_mapped;
+ bool check_large, check_huge_mapped, allow_nomap;
char *start = addr;
char *end = start + len;
@@ -405,11 +405,20 @@ static bool __check_pmd_huge(void *addr, size_t len, int nr_hpages,
if (nr_hpages > 0) {
check_large = true;
granule = hpage_size;
+ if (granule == pmd_pagesize)
+ check_huge_mapped = true;
+ else
+ check_huge_mapped = false;
} else {
check_large = false;
granule = psize();
}
The else is for nr_hpages == 0? But it looks like we allow negative
nr_hpages. Maybe add a bool expect_huge = nr_hpages > 0 to make it
explicit.
Fair enough. I'll change.
granule is an optimization for PAGE_IS_HUGE scanning? When we expect a
PMD mapping, we just scan at pmd_pagesize granularity, otherwise we
check every single page?
At the high level, the function looks good to me, the rules are:
1. if hpage_size == pmd_pagesize, we need to check PAGE_IS_HUGE and
check_large_folio() can be skipped, since we only care about mappings.
This checks for PMD mappings.
2. in other cases, check_large_folios() is always needed. This is for
mTHP checks.
Yes, this is also what I thought. And the following code looks good to me. Thanks.
Exactly, but for some testcase where use this function, doesn't
trigger split of large _folio but only check the HUGE MAP is removed
(nr_hpage == 0), it skips the chekc_large_folio().
I think the ifs at the beginning is confusing. Can we do something like
below to get rid of the ifs? I also moved KPF_* checks in a separate
function. Feel free to make changes if you find any issue there.
static bool check_huge_type(uint64_t categories, uint64_t kpageflags,
enum check_huge_type type)
{
bool file = categories & PAGE_IS_FILE;
bool swapbacked = kpageflags & KPF_SWAPBACKED;
switch (type) {
case CHECK_HUGE_ANON:
return !file;
case CHECK_HUGE_FILE:
return file && !swapbacked;
case CHECK_HUGE_SHMEM:
return file && swapbacked;
}
return false;
}
static bool __check_huge(void *addr, size_t len, int nr_hpages,
uint64_t hpage_size, enum check_huge_type type)
{
int pagemap_fd, kpageflags_fd;
int nr_pmd_mappings = 0;
uint64_t pmd_pagesize, scan_mapping_size;
uint64_t categories, kpf;
unsigned long pfn;
bool check_pmd_mapping;
bool allow_nonpresent;
bool ret = false;
char *start = addr;
char *end = start + len;
pmd_pagesize = read_pmd_pagesize();
if (!pmd_pagesize)
ksft_exit_fail_msg("reading PMD pagesize failed\n");
check_pmd_mapping = hpage_size == pmd_pagesize;
scan_mapping_size = nr_hpages > 0 ? hpage_size : psize();
/* Some mTHP tests check a partially populated PMD-sized range. */
allow_nonpresent = (uint64_t)nr_hpages * hpage_size < len;
pagemap_fd = open(PAGEMAP_PATH, O_RDONLY);
if (pagemap_fd < 0)
ksft_exit_fail_msg("open pagemap fail\n");
kpageflags_fd = open(KPAGEFLAGS_PATH, O_RDONLY);
if (kpageflags_fd < 0) {
close(pagemap_fd);
ksft_exit_fail_msg("open kpageflags fail\n");
}
/* PTE-mapped large folios cannot be identified by PAGE_IS_HUGE. */
if (!check_pmd_mapping &&
!check_large_folios(pagemap_fd, kpageflags_fd, addr, len,
nr_hpages, hpage_size))
goto out;
for (; start < end; start += scan_mapping_size) {
categories = pagemap_scan_get_categories(pagemap_fd, start);
pfn = pagemap_get_pfn(pagemap_fd, start);
if (pfn == -1UL) {
if (!allow_nonpresent)
goto out;
continue;
}
if (pageflags_get(pfn, kpageflags_fd, &kpf))
ksft_exit_fail_msg("read kpageflags: %s\n", strerror(errno));
if (check_pmd_mapping && (categories & PAGE_IS_HUGE))
nr_pmd_mappings++;
if (kpf & KPF_COMPOUND_TAIL)
continue;
if (!check_huge_type(categories, kpf, type))
goto out;
}
if (check_pmd_mapping && nr_pmd_mappings != nr_hpages)
goto out;
Again, because of collapse_full_of_compound() testcase,
it would be failed for this. so, it would better to skip
check_large_folioes() when nr_hpages is 0.
IIUC, when nr_hpages is 0, we should also call check_large_folios() to verify that there are no large folios within this address range, which is also what the previous code did.
Also, I tried Zi's code, and it passed all my khugepaged selftests. I'm not sure why you saw the collapse_full_of_compound() test case fail.