* [PATCH 1/2] kselftest: mm: prevent random failure of huge page split for khugepaged
2026-08-20 19:40 [PATCH 0/2] kselftest: mm: fix some failure of split_huge_page_test Yeoreum Yun
@ 2026-08-20 19:40 ` Yeoreum Yun
2026-08-20 19:51 ` Zi Yan
2026-08-20 19:40 ` [PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper Yeoreum Yun
1 sibling, 1 reply; 7+ messages in thread
From: Yeoreum Yun @ 2026-08-20 19:40 UTC (permalink / raw)
To: Andrew Morton, David Hildenbrand, Lorenzo Stoakes, Zi Yan,
Baolin Wang, Liam R. Howlett, Nico Pache, Ryan Roberts, Dev Jain,
Barry Song, Lance Yang, Usama Arif, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Shuah Khan,
Kevin Brodsky
Cc: linux-mm, linux-kselftest, linux-kernel, Yeoreum Yun
There're some random failure for split_huge_page_test when khugepaged
collapses pages into pmd again which had split by the test.
Prevent the khugepaged's collapses for split page by setting the
mapped pmd-huge-page with MADV_NOHUGEPAGE before split.
Reported-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
tools/testing/selftests/mm/split_huge_page_test.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 32b991472f744..99b45e5518199 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -303,6 +303,9 @@ static void verify_rss_anon_split_huge_page_all_zeroes(char *one_page, int nr_hp
if (!rss_anon_before)
ksft_exit_fail_msg("No RssAnon is allocated before split\n");
+ /* Prevent khugepaged from collapsing the pages. */
+ madvise(one_page, len, MADV_NOHUGEPAGE);
+
/* split all THPs */
write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
(uint64_t)one_page + len, 0);
@@ -350,6 +353,9 @@ static void split_pmd_thp_to_order(int order)
if (!check_huge_anon(one_page, 4, pmd_pagesize))
ksft_exit_fail_msg("No THP is allocated\n");
+ /* Prevent khugepaged from collapsing the pages. */
+ madvise(one_page, len, MADV_NOHUGEPAGE);
+
/* split all THPs */
write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
(uint64_t)one_page + len, order);
@@ -436,6 +442,9 @@ static void split_pte_mapped_thp(void)
goto out;
}
+ /* Prevent khugepaged from collapsing the pages. */
+ madvise(thp_area, thp_area_size, MADV_NOHUGEPAGE);
+
/* Split all THPs through the remapped pages. */
write_debugfs(PID_FMT, getpid(), (uint64_t)page_area,
(uint64_t)page_area + page_area_size, 0);
@@ -665,6 +674,8 @@ static int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size,
ksft_test_result_skip("Pagecache folio split skipped\n");
return -2;
}
+ /* Prevent khugepaged from collapsing the pages. */
+ madvise(*addr, fd_size, MADV_NOHUGEPAGE);
return 0;
err_out_close:
close(*fd);
--
2.43.0
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper
2026-08-20 19:40 [PATCH 0/2] kselftest: mm: fix some failure of split_huge_page_test Yeoreum Yun
2026-08-20 19:40 ` [PATCH 1/2] kselftest: mm: prevent random failure of huge page split for khugepaged Yeoreum Yun
@ 2026-08-20 19:40 ` Yeoreum Yun
2026-08-20 19:55 ` Zi Yan
1 sibling, 1 reply; 7+ messages in thread
From: Yeoreum Yun @ 2026-08-20 19:40 UTC (permalink / raw)
To: Andrew Morton, David Hildenbrand, Lorenzo Stoakes, Zi Yan,
Baolin Wang, Liam R. Howlett, Nico Pache, Ryan Roberts, Dev Jain,
Barry Song, Lance Yang, Usama Arif, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Shuah Khan,
Kevin Brodsky
Cc: linux-mm, linux-kselftest, linux-kernel, 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_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 and change the meaning of
check_huge_xxx()'s nr_hpages argument:
- nr_hpages > 0: check all of pages in the range are huge page.
- nr_hpages < 0: check all of pages in the range are not huge page.
- nr_hpages == 0: invalid.
Reported-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
tools/testing/selftests/mm/khugepaged.c | 26 ++---
tools/testing/selftests/mm/split_huge_page_test.c | 6 +-
tools/testing/selftests/mm/vm_util.c | 135 ++++++++++++++++++----
tools/testing/selftests/mm/vm_util.h | 1 +
4 files changed, 131 insertions(+), 37 deletions(-)
diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 10e8dedcb087d..2e4665e6d5852 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -533,7 +533,7 @@ static void __madvise_collapse(const char *msg, char *p, int nr_hpages,
ret = madvise_collapse_retry(p, nr_hpages * hpage_pmd_size);
if (((bool)ret) == expect)
fail("Fail: Bad return value");
- else if (!ops->check_huge(p, expect ? nr_hpages : 0))
+ else if (!ops->check_huge(p, expect ? nr_hpages : -nr_hpages))
fail("Fail: check_huge()");
else
success("OK");
@@ -545,7 +545,7 @@ static void madvise_collapse(const char *msg, char *p, int nr_hpages,
struct mem_ops *ops, bool expect)
{
/* Sanity check */
- if (!ops->check_huge(p, 0))
+ if (!ops->check_huge(p, -nr_hpages))
ksft_exit_fail_msg("Unexpected huge page\n");
__madvise_collapse(msg, p, nr_hpages, ops, expect);
}
@@ -558,7 +558,7 @@ static bool wait_for_scan(const char *msg, char *p, int nr_hpages,
int timeout = 6; /* 3 seconds */
/* Sanity check */
- if (!ops->check_huge(p, 0))
+ if (!ops->check_huge(p, -nr_hpages))
ksft_exit_fail_msg("Unexpected huge page\n");
madvise(p, nr_hpages * hpage_pmd_size, MADV_HUGEPAGE);
@@ -605,7 +605,7 @@ static void khugepaged_collapse(const char *msg, char *p, int nr_hpages,
if (ops != &__anon_ops)
ops->fault(p, 0, nr_hpages * hpage_pmd_size);
- if (ops->check_huge(p, expect ? nr_hpages : 0))
+ if (ops->check_huge(p, expect ? nr_hpages : -nr_hpages))
success("OK");
else
fail("Fail");
@@ -643,7 +643,7 @@ static void alloc_at_fault(void)
madvise(p, page_size, MADV_DONTNEED);
ksft_print_msg("Split huge PMD on MADV_DONTNEED...");
- if (check_huge_anon(p, 0, hpage_pmd_size))
+ if (check_huge_anon(p, -1, hpage_pmd_size))
success("OK");
else
fail("Fail");
@@ -815,7 +815,7 @@ static void collapse_single_pte_entry_compound(struct collapse_context *c, struc
madvise(p, hpage_pmd_size, MADV_NOHUGEPAGE);
ksft_print_msg("Split huge page leaving single PTE mapping compound page...");
madvise(p + page_size, hpage_pmd_size - page_size, MADV_DONTNEED);
- if (ops->check_huge(p, 0))
+ if (ops->check_huge(p, -1))
success("OK");
else
fail("Fail");
@@ -836,7 +836,7 @@ static void collapse_full_of_compound(struct collapse_context *c, struct mem_ops
ksft_print_msg("Split huge page leaving single PTE page table full of compound pages...");
madvise(p, page_size, MADV_NOHUGEPAGE);
madvise(p, hpage_pmd_size, MADV_NOHUGEPAGE);
- if (ops->check_huge(p, 0))
+ if (ops->check_huge(p, -1))
success("OK");
else
fail("Fail");
@@ -903,7 +903,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
ksft_print_msg("Allocate small page...");
ops->fault(p, 0, page_size);
- if (ops->check_huge(p, 0))
+ if (ops->check_huge(p, -1))
success("OK");
else
fail("Fail");
@@ -911,7 +911,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
ksft_print_msg("Share small page over fork()...");
if (!fork()) {
/* Do not touch settings on child exit */
- if (ops->check_huge(p, 0))
+ if (ops->check_huge(p, -1))
success("OK");
else
fail("Fail");
@@ -929,7 +929,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
exit_status = WEXITSTATUS(wstatus);
ksft_print_msg("Check if parent still has small page...");
- if (ops->check_huge(p, 0))
+ if (ops->check_huge(p, -1))
success("OK");
else
fail("Fail");
@@ -955,7 +955,7 @@ static void collapse_fork_compound(struct collapse_context *c, struct mem_ops *o
ksft_print_msg("Split huge page PMD in child process...");
madvise(p, page_size, MADV_NOHUGEPAGE);
madvise(p, hpage_pmd_size, MADV_NOHUGEPAGE);
- if (ops->check_huge(p, 0))
+ if (ops->check_huge(p, -1))
success("OK");
else
fail("Fail");
@@ -1003,7 +1003,7 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
ksft_print_msg("Trigger CoW on page %d of %d...",
hpage_pmd_nr - max_ptes_shared - 1, hpage_pmd_nr);
ops->fault(p, 0, (hpage_pmd_nr - max_ptes_shared - 1) * page_size);
- if (ops->check_huge(p, 0))
+ if (ops->check_huge(p, -1))
success("OK");
else
fail("Fail");
@@ -1016,7 +1016,7 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
hpage_pmd_nr - max_ptes_shared, hpage_pmd_nr);
ops->fault(p, 0, (hpage_pmd_nr - max_ptes_shared) *
page_size);
- if (ops->check_huge(p, 0))
+ if (ops->check_huge(p, -1))
success("OK");
else
fail("Fail");
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 99b45e5518199..4fcd330cf0726 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -314,7 +314,7 @@ static void verify_rss_anon_split_huge_page_all_zeroes(char *one_page, int nr_hp
if (one_page[i] != (char)0)
ksft_exit_fail_msg("%ld byte corrupted\n", i);
- if (!check_huge_anon(one_page, 0, pmd_pagesize))
+ if (!check_huge_anon(one_page, -nr_hpages, pmd_pagesize))
ksft_exit_fail_msg("Still AnonHugePages not split\n");
rss_anon_after = rss_anon();
@@ -372,7 +372,7 @@ static void split_pmd_thp_to_order(int order)
(pmd_order + 1)))
ksft_exit_fail_msg("Unexpected THP split\n");
- if (!check_huge_anon(one_page, 0, pmd_pagesize))
+ if (!check_huge_anon(one_page, -4, pmd_pagesize))
ksft_exit_fail_msg("Still AnonHugePages not split\n");
ksft_test_result_pass("Split huge pages to order %d successful\n", order);
@@ -746,7 +746,7 @@ static void split_thp_in_pagecache_to_order_at(size_t fd_size,
goto out;
}
- if (!check_huge_file(addr, 0, pmd_pagesize)) {
+ if (!check_huge_file(addr, -(fd_size / pmd_pagesize), pmd_pagesize)) {
ksft_print_msg("Still FilePmdMapped not split\n");
err = EXIT_FAILURE;
goto out;
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 311fc5b4513eb..166d5d79289f3 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -14,6 +14,8 @@
#define PMD_SIZE_FILE_PATH "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
#define SMAP_FILE_PATH "/proc/self/smaps"
#define STATUS_FILE_PATH "/proc/self/status"
+#define PAGEMAP_FILE_PATH "/proc/self/pagemap"
+#define KPAGEFLAGS_FILE_PATH "/proc/kpageflags"
#define MAX_LINE_LENGTH 500
unsigned int __page_size;
@@ -229,37 +231,128 @@ char *__get_smap_entry(void *addr, const char *pattern, char *buf, size_t len)
return entry;
}
-bool __check_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));
-}
-
bool check_huge_anon(void *addr, int nr_hpages, uint64_t hpage_size)
{
- return __check_huge(addr, "AnonHugePages: ", nr_hpages, hpage_size);
+ int i, pagemap_fd, nr = 0;
+ uint64_t categories;
+ bool expect_huge;
+
+ if (nr_hpages == 0 || hpage_size == 0)
+ return false;
+
+ if (nr_hpages < 0) {
+ nr_hpages = -nr_hpages;
+ expect_huge = false;
+ } else
+ expect_huge = true;
+
+ pagemap_fd = open(PAGEMAP_FILE_PATH, O_RDONLY);
+ if (pagemap_fd < 0)
+ ksft_exit_fail_msg("open pagemap: %s\n", strerror(errno));
+
+ for (i = 0; i < nr_hpages; i++, addr += hpage_size) {
+ categories = pagemap_scan_get_categories(pagemap_fd, addr);
+ if (!(categories & PAGE_IS_HUGE))
+ continue;
+ if (categories & PAGE_IS_FILE)
+ continue;
+ nr++;
+ }
+
+ close(pagemap_fd);
+ return expect_huge ? nr == nr_hpages : nr == 0;
}
bool check_huge_file(void *addr, int nr_hpages, uint64_t hpage_size)
{
- return __check_huge(addr, "FilePmdMapped:", nr_hpages, hpage_size);
+ int i, pagemap_fd, kpf_fd, nr = 0;
+ unsigned long pfn;
+ uint64_t categories, kpf;
+ bool expect_huge;
+
+ if (nr_hpages == 0 || hpage_size == 0)
+ return false;
+
+ if (nr_hpages < 0) {
+ nr_hpages = -nr_hpages;
+ expect_huge = false;
+ } else
+ expect_huge = true;
+
+ pagemap_fd = open(PAGEMAP_FILE_PATH, O_RDONLY);
+ if (pagemap_fd < 0)
+ ksft_exit_fail_msg("open pagemap: %s\n", strerror(errno));
+
+ kpf_fd = open(KPAGEFLAGS_FILE_PATH, O_RDONLY);
+ if (kpf_fd < 0)
+ ksft_exit_fail_msg("open kpageflags: %s\n", strerror(errno));
+
+ for (i = 0; i < nr_hpages; i++, addr += hpage_size) {
+ categories = pagemap_scan_get_categories(pagemap_fd, addr);
+ pfn = pagemap_get_pfn(pagemap_fd, addr);
+ if (pfn == -1UL)
+ continue;
+ if (pageflags_get(pfn, kpf_fd, &kpf))
+ ksft_exit_fail_msg("read kpageflags: %s\n", strerror(errno));
+ if (!(categories & PAGE_IS_HUGE))
+ continue;
+ if (!(categories & PAGE_IS_FILE))
+ continue;
+ if (kpf & KPF_SWAPBACKED)
+ continue;
+ nr++;
+ }
+
+ close(pagemap_fd);
+ close(kpf_fd);
+
+ return expect_huge ? nr == nr_hpages : nr == 0;
}
bool check_huge_shmem(void *addr, int nr_hpages, uint64_t hpage_size)
{
- return __check_huge(addr, "ShmemPmdMapped:", nr_hpages, hpage_size);
+ int i, pagemap_fd, kpf_fd, nr = 0;
+ unsigned long pfn;
+ uint64_t categories, kpf;
+ bool expect_huge;
+
+ if (nr_hpages == 0 || hpage_size == 0)
+ return false;
+
+ if (nr_hpages < 0) {
+ nr_hpages = -nr_hpages;
+ expect_huge = true;
+ } else
+ expect_huge = false;
+
+ pagemap_fd = open(PAGEMAP_FILE_PATH, O_RDONLY);
+ if (pagemap_fd < 0)
+ ksft_exit_fail_msg("open pagemap: %s\n", strerror(errno));
+
+ kpf_fd = open(KPAGEFLAGS_FILE_PATH, O_RDONLY);
+ if (kpf_fd < 0)
+ ksft_exit_fail_msg("open kpageflags: %s\n", strerror(errno));
+
+ for (i = 0; i < nr_hpages; i++, addr += hpage_size) {
+ categories = pagemap_scan_get_categories(pagemap_fd, addr);
+ pfn = pagemap_get_pfn(pagemap_fd, addr);
+ if (pfn == -1UL)
+ continue;
+ if (pageflags_get(pfn, kpf_fd, &kpf))
+ ksft_exit_fail_msg("read kpageflags: %s\n", strerror(errno));
+ if (!(categories & PAGE_IS_HUGE))
+ continue;
+ if (!(categories & PAGE_IS_FILE))
+ continue;
+ if (!(kpf & KPF_SWAPBACKED))
+ continue;
+ nr++;
+ }
+
+ close(pagemap_fd);
+ close(kpf_fd);
+
+ return expect_huge ? nr == nr_hpages : nr == 0;
}
int64_t allocate_transhuge(void *ptr, int pagemap_fd)
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index ea8fc8fdf0eb0..0a1627f36efc3 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -18,6 +18,7 @@
#define PM_SWAP BIT_ULL(62)
#define PM_PRESENT BIT_ULL(63)
+#define KPF_SWAPBACKED BIT_ULL(14)
#define KPF_COMPOUND_HEAD BIT_ULL(15)
#define KPF_COMPOUND_TAIL BIT_ULL(16)
#define KPF_HWPOISON BIT_ULL(19)
--
2.43.0
^ permalink raw reply related [flat|nested] 7+ messages in thread