[PATCH 3/4] selftests/mm: factor out THP split helpers
From: Sarthak Sharma
Date: Thu Nov 12 2026 - 04:17:12 EST
split_huge_page_test.c contains helpers to split huge pages using
the split_huge_pages debugfs interface. A later patch adds a THP
compaction selftest and needs the same functionality.
Move write_debugfs() to vm_util.c. Add wrappers for splitting
process mappings, mappings with an offset within folio and file
backed folios. Also add a helper to check if the debugfs interface
is available.
Update split_huge_page_test.c to use the shared helpers and
also remove the unused SMAP_PATH definition.
Signed-off-by: Sarthak Sharma <sarthak.sharma@xxxxxxx>
---
.../selftests/mm/split_huge_page_test.c | 45 +++------------
tools/testing/selftests/mm/vm_util.c | 56 +++++++++++++++++++
tools/testing/selftests/mm/vm_util.h | 6 ++
3 files changed, 69 insertions(+), 38 deletions(-)
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 33a2473327bb..330a453e6402 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -8,7 +8,6 @@
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
-#include <stdarg.h>
#include <unistd.h>
#include <inttypes.h>
#include <string.h>
@@ -28,14 +27,8 @@ uint64_t pmd_pagesize;
unsigned int pmd_order;
int *expected_orders;
-#define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages"
-#define SMAP_PATH "/proc/self/smaps"
#define INPUT_MAX 80
-#define PID_FMT "%d,0x%lx,0x%lx,%d"
-#define PID_FMT_OFFSET "%d,0x%lx,0x%lx,%d,%d"
-#define PATH_FMT "%s,0x%lx,0x%lx,%d"
-
const char *pagemap_proc = "/proc/self/pagemap";
const char *kpageflags_proc = "/proc/kpageflags";
int pagemap_fd;
@@ -70,25 +63,6 @@ static int check_after_split_folio_orders(char *vaddr_start, size_t len,
return status;
}
-static void write_debugfs(const char *fmt, ...)
-{
- char input[INPUT_MAX];
- int ret;
- va_list argp;
-
- va_start(argp, fmt);
- ret = vsnprintf(input, INPUT_MAX, fmt, argp);
- va_end(argp);
-
- if (ret >= INPUT_MAX)
- ksft_exit_fail_msg("%s: Debugfs input is too long\n", __func__);
-
- ret = write_file(SPLIT_DEBUGFS, input, ret + 1);
- if (ret)
- ksft_exit_fail_msg("write_file(%s): %s\n", SPLIT_DEBUGFS,
- strerror(-ret));
-}
-
static char *allocate_zero_filled_hugepage(size_t len)
{
char *result;
@@ -132,8 +106,7 @@ static void verify_rss_anon_split_huge_page_all_zeroes(char *one_page, int nr_hp
disable_khugepaged(one_page, len);
/* split all THPs */
- write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
- (uint64_t)one_page + len, 0);
+ split_huge_pages(one_page, len, 0);
for (i = 0; i < len; i++)
if (one_page[i] != (char)0)
@@ -181,8 +154,7 @@ static void split_pmd_thp_to_order(int order)
disable_khugepaged(one_page, len);
/* split all THPs */
- write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
- (uint64_t)one_page + len, order);
+ split_huge_pages(one_page, len, order);
for (i = 0; i < len; i++)
if (one_page[i] != (char)i)
@@ -269,8 +241,7 @@ static void split_pte_mapped_thp(void)
}
/* Split all THPs through the remapped pages. */
- write_debugfs(PID_FMT, getpid(), (uint64_t)page_area,
- (uint64_t)page_area + page_area_size, 0);
+ split_huge_pages(page_area, page_area_size, 0);
/* Corruption during mremap or split? */
for (i = 0; i < page_area_size; i++) {
@@ -306,7 +277,7 @@ static void split_file_backed_thp(int order)
char opts[64];
ssize_t num_written, num_read;
char *file_buf1 = NULL, *file_buf2 = NULL;
- uint64_t pgoff_start = 0, pgoff_end = 1024;
+ unsigned long pgoff_start = 0, pgoff_end = 1024;
int i;
ksft_print_msg("Please enable pr_debug in split_huge_pages_in_file() for more info.\n");
@@ -355,7 +326,7 @@ static void split_file_backed_thp(int order)
}
/* split the file-backed THP */
- write_debugfs(PATH_FMT, testfile, pgoff_start, pgoff_end, order);
+ split_huge_pages_file(testfile, pgoff_start, pgoff_end, order);
/* check file content after split */
status = lseek(fd, 0, SEEK_SET);
@@ -536,16 +507,14 @@ static void split_thp_in_pagecache_to_order_at(size_t fd_size,
*/
if (offset == -1) {
for (split_addr = addr; split_addr < addr + fd_size; split_addr += pmd_pagesize)
- write_debugfs(PID_FMT, getpid(), (uint64_t)split_addr,
- (uint64_t)split_addr + pagesize, order);
+ split_huge_pages(split_addr, pagesize, order);
expected_orders[order] = fd_size / (pagesize << order);
} else {
int times = fd_size / pmd_pagesize;
for (split_addr = addr; split_addr < addr + fd_size; split_addr += pmd_pagesize)
- write_debugfs(PID_FMT_OFFSET, getpid(), (uint64_t)split_addr,
- (uint64_t)split_addr + pagesize, order, offset);
+ split_huge_pages_with_offset(split_addr, pagesize, order, offset);
for (i = order + 1; i < pmd_order; i++)
expected_orders[i] = times;
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 9942bbea7837..b64c651f753e 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -18,6 +18,12 @@
#define PAGEMAP_PATH "/proc/self/pagemap"
#define KPAGEFLAGS_PATH "/proc/kpageflags"
#define MAX_NR_ORDERS 20
+#define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages"
+#define INPUT_MAX 80
+
+#define PID_FMT "%d,0x%lx,0x%lx,%d"
+#define PID_FMT_OFFSET "%d,0x%lx,0x%lx,%d,%d"
+#define PATH_FMT "%s,0x%lx,0x%lx,%d"
unsigned int __page_size;
unsigned int __page_shift;
@@ -1105,6 +1111,56 @@ int unpoison_memory(unsigned long pfn)
return ret > 0 ? 0 : -errno;
}
+static void write_debugfs(const char *fmt, ...)
+{
+ char input[INPUT_MAX];
+ int ret;
+ va_list argp;
+
+ va_start(argp, fmt);
+ ret = vsnprintf(input, INPUT_MAX, fmt, argp);
+ va_end(argp);
+
+ if (ret >= INPUT_MAX)
+ ksft_exit_fail_msg("%s: Debugfs input is too long\n", __func__);
+
+ ret = write_file(SPLIT_DEBUGFS, input, ret + 1);
+ if (ret)
+ ksft_exit_fail_msg("write_file(%s): %s\n", SPLIT_DEBUGFS,
+ strerror(-ret));
+}
+
+bool split_huge_pages_supported(void)
+{
+ int fd;
+
+ fd = open(SPLIT_DEBUGFS, O_WRONLY);
+ if (fd < 0)
+ return false;
+
+ close(fd);
+ return true;
+}
+
+void split_huge_pages(void *addr, size_t len, int order)
+{
+ write_debugfs(PID_FMT, getpid(), (unsigned long)addr,
+ (unsigned long)addr + len, order);
+}
+
+void split_huge_pages_with_offset(void *addr, size_t len, int order,
+ int offset)
+{
+ write_debugfs(PID_FMT_OFFSET, getpid(), (unsigned long)addr,
+ (unsigned long)addr + len, order, offset);
+}
+
+void split_huge_pages_file(const char *path, unsigned long start,
+ unsigned long end, int order)
+{
+ write_debugfs(PATH_FMT, path, start, end, order);
+}
+
static unsigned long shmall, shmmax;
void __shm_limits_restore(void)
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index ef8fe76d4c61..efd3a2be945d 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -118,6 +118,12 @@ bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
int kpageflags_fd);
bool is_range_backed_by_order(char *start, size_t len, int order,
int pagemap_fd, int kpageflags_fd);
+bool split_huge_pages_supported(void);
+void split_huge_pages(void *addr, size_t len, int order);
+void split_huge_pages_with_offset(void *addr, size_t len, int order,
+ int offset);
+void split_huge_pages_file(const char *path, unsigned long start,
+ unsigned long end, int order);
int uffd_register(int uffd, void *addr, uint64_t len,
bool miss, bool wp, bool minor);
--
2.53.0