Merge tag 'mm-stable-2025-10-01-19-00' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull MM updates from Andrew Morton:

 - "mm, swap: improve cluster scan strategy" from Kairui Song improves
   performance and reduces the failure rate of swap cluster allocation

 - "support large align and nid in Rust allocators" from Vitaly Wool
   permits Rust allocators to set NUMA node and large alignment when
   perforning slub and vmalloc reallocs

 - "mm/damon/vaddr: support stat-purpose DAMOS" from Yueyang Pan extend
   DAMOS_STAT's handling of the DAMON operations sets for virtual
   address spaces for ops-level DAMOS filters

 - "execute PROCMAP_QUERY ioctl under per-vma lock" from Suren
   Baghdasaryan reduces mmap_lock contention during reads of
   /proc/pid/maps

 - "mm/mincore: minor clean up for swap cache checking" from Kairui Song
   performs some cleanup in the swap code

 - "mm: vm_normal_page*() improvements" from David Hildenbrand provides
   code cleanup in the pagemap code

 - "add persistent huge zero folio support" from Pankaj Raghav provides
   a block layer speedup by optionalls making the
   huge_zero_pagepersistent, instead of releasing it when its refcount
   falls to zero

 - "kho: fixes and cleanups" from Mike Rapoport adds a few touchups to
   the recently added Kexec Handover feature

 - "mm: make mm->flags a bitmap and 64-bit on all arches" from Lorenzo
   Stoakes turns mm_struct.flags into a bitmap. To end the constant
   struggle with space shortage on 32-bit conflicting with 64-bit's
   needs

 - "mm/swapfile.c and swap.h cleanup" from Chris Li cleans up some swap
   code

 - "selftests/mm: Fix false positives and skip unsupported tests" from
   Donet Tom fixes a few things in our selftests code

 - "prctl: extend PR_SET_THP_DISABLE to only provide THPs when advised"
   from David Hildenbrand "allows individual processes to opt-out of
   THP=always into THP=madvise, without affecting other workloads on the
   system".

   It's a long story - the [1/N] changelog spells out the considerations

 - "Add and use memdesc_flags_t" from Matthew Wilcox gets us started on
   the memdesc project. Please see

      https://kernelnewbies.org/MatthewWilcox/Memdescs and
      https://blogs.oracle.com/linux/post/introducing-memdesc

 - "Tiny optimization for large read operations" from Chi Zhiling
   improves the efficiency of the pagecache read path

 - "Better split_huge_page_test result check" from Zi Yan improves our
   folio splitting selftest code

 - "test that rmap behaves as expected" from Wei Yang adds some rmap
   selftests

 - "remove write_cache_pages()" from Christoph Hellwig removes that
   function and converts its two remaining callers

 - "selftests/mm: uffd-stress fixes" from Dev Jain fixes some UFFD
   selftests issues

 - "introduce kernel file mapped folios" from Boris Burkov introduces
   the concept of "kernel file pages". Using these permits btrfs to
   account its metadata pages to the root cgroup, rather than to the
   cgroups of random inappropriate tasks

 - "mm/pageblock: improve readability of some pageblock handling" from
   Wei Yang provides some readability improvements to the page allocator
   code

 - "mm/damon: support ARM32 with LPAE" from SeongJae Park teaches DAMON
   to understand arm32 highmem

 - "tools: testing: Use existing atomic.h for vma/maple tests" from
   Brendan Jackman performs some code cleanups and deduplication under
   tools/testing/

 - "maple_tree: Fix testing for 32bit compiles" from Liam Howlett fixes
   a couple of 32-bit issues in tools/testing/radix-tree.c

 - "kasan: unify kasan_enabled() and remove arch-specific
   implementations" from Sabyrzhan Tasbolatov moves KASAN arch-specific
   initialization code into a common arch-neutral implementation

 - "mm: remove zpool" from Johannes Weiner removes zspool - an
   indirection layer which now only redirects to a single thing
   (zsmalloc)

 - "mm: task_stack: Stack handling cleanups" from Pasha Tatashin makes a
   couple of cleanups in the fork code

 - "mm: remove nth_page()" from David Hildenbrand makes rather a lot of
   adjustments at various nth_page() callsites, eventually permitting
   the removal of that undesirable helper function

 - "introduce kasan.write_only option in hw-tags" from Yeoreum Yun
   creates a KASAN read-only mode for ARM, using that architecture's
   memory tagging feature. It is felt that a read-only mode KASAN is
   suitable for use in production systems rather than debug-only

 - "mm: hugetlb: cleanup hugetlb folio allocation" from Kefeng Wang does
   some tidying in the hugetlb folio allocation code

 - "mm: establish const-correctness for pointer parameters" from Max
   Kellermann makes quite a number of the MM API functions more accurate
   about the constness of their arguments. This was getting in the way
   of subsystems (in this case CEPH) when they attempt to improving
   their own const/non-const accuracy

 - "Cleanup free_pages() misuse" from Vishal Moola fixes a number of
   code sites which were confused over when to use free_pages() vs
   __free_pages()

 - "Add Rust abstraction for Maple Trees" from Alice Ryhl makes the
   mapletree code accessible to Rust. Required by nouveau and by its
   forthcoming successor: the new Rust Nova driver

 - "selftests/mm: split_huge_page_test: split_pte_mapped_thp
   improvements" from David Hildenbrand adds a fix and some cleanups to
   the thp selftesting code

 - "mm, swap: introduce swap table as swap cache (phase I)" from Chris
   Li and Kairui Song is the first step along the path to implementing
   "swap tables" - a new approach to swap allocation and state tracking
   which is expected to yield speed and space improvements. This
   patchset itself yields a 5-20% performance benefit in some situations

 - "Some ptdesc cleanups" from Matthew Wilcox utilizes the new memdesc
   layer to clean up the ptdesc code a little

 - "Fix va_high_addr_switch.sh test failure" from Chunyu Hu fixes some
   issues in our 5-level pagetable selftesting code

 - "Minor fixes for memory allocation profiling" from Suren Baghdasaryan
   addresses a couple of minor issues in relatively new memory
   allocation profiling feature

 - "Small cleanups" from Matthew Wilcox has a few cleanups in
   preparation for more memdesc work

 - "mm/damon: add addr_unit for DAMON_LRU_SORT and DAMON_RECLAIM" from
   Quanmin Yan makes some changes to DAMON in furtherance of supporting
   arm highmem

 - "selftests/mm: Add -Wunreachable-code and fix warnings" from Muhammad
   Anjum adds that compiler check to selftests code and fixes the
   fallout, by removing dead code

 - "Improvements to Victim Process Thawing and OOM Reaper Traversal
   Order" from zhongjinji makes a number of improvements in the OOM
   killer: mainly thawing a more appropriate group of victim threads so
   they can release resources

 - "mm/damon: misc fixups and improvements for 6.18" from SeongJae Park
   is a bunch of small and unrelated fixups for DAMON

 - "mm/damon: define and use DAMON initialization check function" from
   SeongJae Park implement reliability and maintainability improvements
   to a recently-added bug fix

 - "mm/damon/stat: expose auto-tuned intervals and non-idle ages" from
   SeongJae Park provides additional transparency to userspace clients
   of the DAMON_STAT information

 - "Expand scope of khugepaged anonymous collapse" from Dev Jain removes
   some constraints on khubepaged's collapsing of anon VMAs. It also
   increases the success rate of MADV_COLLAPSE against an anon vma

 - "mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()"
   from Lorenzo Stoakes moves us further towards removal of
   file_operations.mmap(). This patchset concentrates upon clearing up
   the treatment of stacked filesystems

 - "mm: Improve mlock tracking for large folios" from Kiryl Shutsemau
   provides some fixes and improvements to mlock's tracking of large
   folios. /proc/meminfo's "Mlocked" field became more accurate

 - "mm/ksm: Fix incorrect accounting of KSM counters during fork" from
   Donet Tom fixes several user-visible KSM stats inaccuracies across
   forks and adds selftest code to verify these counters

 - "mm_slot: fix the usage of mm_slot_entry" from Wei Yang addresses
   some potential but presently benign issues in KSM's mm_slot handling

* tag 'mm-stable-2025-10-01-19-00' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (372 commits)
  mm: swap: check for stable address space before operating on the VMA
  mm: convert folio_page() back to a macro
  mm/khugepaged: use start_addr/addr for improved readability
  hugetlbfs: skip VMAs without shareable locks in hugetlb_vmdelete_list
  alloc_tag: fix boot failure due to NULL pointer dereference
  mm: silence data-race in update_hiwater_rss
  mm/memory-failure: don't select MEMORY_ISOLATION
  mm/khugepaged: remove definition of struct khugepaged_mm_slot
  mm/ksm: get mm_slot by mm_slot_entry() when slot is !NULL
  hugetlb: increase number of reserving hugepages via cmdline
  selftests/mm: add fork inheritance test for ksm_merging_pages counter
  mm/ksm: fix incorrect KSM counter handling in mm_struct during fork
  drivers/base/node: fix double free in register_one_node()
  mm: remove PMD alignment constraint in execmem_vmalloc()
  mm/memory_hotplug: fix typo 'esecially' -> 'especially'
  mm/rmap: improve mlock tracking for large folios
  mm/filemap: map entire large folio faultaround
  mm/fault: try to map the entire file folio in finish_fault()
  mm/rmap: mlock large folios in try_to_unmap_one()
  mm/rmap: fix a mlock race condition in folio_referenced_one()
  ...

1 files changed, 79 insertions, 120 deletions

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index d8bd1911dfc0..ac136f04b8d6 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -38,14 +38,11 @@ enum ksm_merge_mode {
 };
 
 static int mem_fd;
-static int ksm_fd;
-static int ksm_full_scans_fd;
-static int proc_self_ksm_stat_fd;
-static int proc_self_ksm_merging_pages_fd;
-static int ksm_use_zero_pages_fd;
 static int pagemap_fd;
 static size_t pagesize;
 
+static void init_global_file_handles(void);
+
 static bool range_maps_duplicates(char *addr, unsigned long size)
 {
 	unsigned long offs_a, offs_b, pfn_a, pfn_b;
@@ -73,88 +70,6 @@ static bool range_maps_duplicates(char *addr, unsigned long size)
 	return false;
 }
 
-static long get_my_ksm_zero_pages(void)
-{
-	char buf[200];
-	char *substr_ksm_zero;
-	size_t value_pos;
-	ssize_t read_size;
-	unsigned long my_ksm_zero_pages;
-
-	if (!proc_self_ksm_stat_fd)
-		return 0;
-
-	read_size = pread(proc_self_ksm_stat_fd, buf, sizeof(buf) - 1, 0);
-	if (read_size < 0)
-		return -errno;
-
-	buf[read_size] = 0;
-
-	substr_ksm_zero = strstr(buf, "ksm_zero_pages");
-	if (!substr_ksm_zero)
-		return 0;
-
-	value_pos = strcspn(substr_ksm_zero, "0123456789");
-	my_ksm_zero_pages = strtol(substr_ksm_zero + value_pos, NULL, 10);
-
-	return my_ksm_zero_pages;
-}
-
-static long get_my_merging_pages(void)
-{
-	char buf[10];
-	ssize_t ret;
-
-	if (proc_self_ksm_merging_pages_fd < 0)
-		return proc_self_ksm_merging_pages_fd;
-
-	ret = pread(proc_self_ksm_merging_pages_fd, buf, sizeof(buf) - 1, 0);
-	if (ret <= 0)
-		return -errno;
-	buf[ret] = 0;
-
-	return strtol(buf, NULL, 10);
-}
-
-static long ksm_get_full_scans(void)
-{
-	char buf[10];
-	ssize_t ret;
-
-	ret = pread(ksm_full_scans_fd, buf, sizeof(buf) - 1, 0);
-	if (ret <= 0)
-		return -errno;
-	buf[ret] = 0;
-
-	return strtol(buf, NULL, 10);
-}
-
-static int ksm_merge(void)
-{
-	long start_scans, end_scans;
-
-	/* Wait for two full scans such that any possible merging happened. */
-	start_scans = ksm_get_full_scans();
-	if (start_scans < 0)
-		return start_scans;
-	if (write(ksm_fd, "1", 1) != 1)
-		return -errno;
-	do {
-		end_scans = ksm_get_full_scans();
-		if (end_scans < 0)
-			return end_scans;
-	} while (end_scans < start_scans + 2);
-
-	return 0;
-}
-
-static int ksm_unmerge(void)
-{
-	if (write(ksm_fd, "2", 1) != 1)
-		return -errno;
-	return 0;
-}
-
 static char *__mmap_and_merge_range(char val, unsigned long size, int prot,
 				  enum ksm_merge_mode mode)
 {
@@ -163,12 +78,12 @@ static char *__mmap_and_merge_range(char val, unsigned long size, int prot,
 	int ret;
 
 	/* Stabilize accounting by disabling KSM completely. */
-	if (ksm_unmerge()) {
+	if (ksm_stop() < 0) {
 		ksft_print_msg("Disabling (unmerging) KSM failed\n");
 		return err_map;
 	}
 
-	if (get_my_merging_pages() > 0) {
+	if (ksm_get_self_merging_pages() > 0) {
 		ksft_print_msg("Still pages merged\n");
 		return err_map;
 	}
@@ -218,7 +133,7 @@ static char *__mmap_and_merge_range(char val, unsigned long size, int prot,
 	}
 
 	/* Run KSM to trigger merging and wait. */
-	if (ksm_merge()) {
+	if (ksm_start() < 0) {
 		ksft_print_msg("Running KSM failed\n");
 		goto unmap;
 	}
@@ -227,7 +142,7 @@ static char *__mmap_and_merge_range(char val, unsigned long size, int prot,
 	 * Check if anything was merged at all. Ignore the zero page that is
 	 * accounted differently (depending on kernel support).
 	 */
-	if (val && !get_my_merging_pages()) {
+	if (val && !ksm_get_self_merging_pages()) {
 		ksft_print_msg("No pages got merged\n");
 		goto unmap;
 	}
@@ -274,6 +189,7 @@ static void test_unmerge(void)
 	ksft_test_result(!range_maps_duplicates(map, size),
 			 "Pages were unmerged\n");
 unmap:
+	ksm_stop();
 	munmap(map, size);
 }
 
@@ -286,15 +202,12 @@ static void test_unmerge_zero_pages(void)
 
 	ksft_print_msg("[RUN] %s\n", __func__);
 
-	if (proc_self_ksm_stat_fd < 0) {
-		ksft_test_result_skip("open(\"/proc/self/ksm_stat\") failed\n");
-		return;
-	}
-	if (ksm_use_zero_pages_fd < 0) {
-		ksft_test_result_skip("open \"/sys/kernel/mm/ksm/use_zero_pages\" failed\n");
+	if (ksm_get_self_zero_pages() < 0) {
+		ksft_test_result_skip("accessing \"/proc/self/ksm_stat\" failed\n");
 		return;
 	}
-	if (write(ksm_use_zero_pages_fd, "1", 1) != 1) {
+
+	if (ksm_use_zero_pages() < 0) {
 		ksft_test_result_skip("write \"/sys/kernel/mm/ksm/use_zero_pages\" failed\n");
 		return;
 	}
@@ -306,7 +219,7 @@ static void test_unmerge_zero_pages(void)
 
 	/* Check if ksm_zero_pages is updated correctly after KSM merging */
 	pages_expected = size / pagesize;
-	if (pages_expected != get_my_ksm_zero_pages()) {
+	if (pages_expected != ksm_get_self_zero_pages()) {
 		ksft_test_result_fail("'ksm_zero_pages' updated after merging\n");
 		goto unmap;
 	}
@@ -319,7 +232,7 @@ static void test_unmerge_zero_pages(void)
 
 	/* Check if ksm_zero_pages is updated correctly after unmerging */
 	pages_expected /= 2;
-	if (pages_expected != get_my_ksm_zero_pages()) {
+	if (pages_expected != ksm_get_self_zero_pages()) {
 		ksft_test_result_fail("'ksm_zero_pages' updated after unmerging\n");
 		goto unmap;
 	}
@@ -329,7 +242,7 @@ static void test_unmerge_zero_pages(void)
 		*((unsigned int *)&map[offs]) = offs;
 
 	/* Now we should have no zeropages remaining. */
-	if (get_my_ksm_zero_pages()) {
+	if (ksm_get_self_zero_pages()) {
 		ksft_test_result_fail("'ksm_zero_pages' updated after write fault\n");
 		goto unmap;
 	}
@@ -338,6 +251,7 @@ static void test_unmerge_zero_pages(void)
 	ksft_test_result(!range_maps_duplicates(map, size),
 			"KSM zero pages were unmerged\n");
 unmap:
+	ksm_stop();
 	munmap(map, size);
 }
 
@@ -366,6 +280,7 @@ static void test_unmerge_discarded(void)
 	ksft_test_result(!range_maps_duplicates(map, size),
 			 "Pages were unmerged\n");
 unmap:
+	ksm_stop();
 	munmap(map, size);
 }
 
@@ -452,6 +367,7 @@ static void test_unmerge_uffd_wp(void)
 close_uffd:
 	close(uffd);
 unmap:
+	ksm_stop();
 	munmap(map, size);
 }
 #endif
@@ -506,27 +422,30 @@ static int test_child_ksm(void)
 
 	/* Test if KSM is enabled for the process. */
 	if (prctl(PR_GET_MEMORY_MERGE, 0, 0, 0, 0) != 1)
-		return -1;
+		return 1;
 
 	/* Test if merge could really happen. */
 	map = __mmap_and_merge_range(0xcf, size, PROT_READ | PROT_WRITE, KSM_MERGE_NONE);
 	if (map == MAP_MERGE_FAIL)
-		return -2;
+		return 2;
 	else if (map == MAP_MERGE_SKIP)
-		return -3;
+		return 3;
 
+	ksm_stop();
 	munmap(map, size);
 	return 0;
 }
 
 static void test_child_ksm_err(int status)
 {
-	if (status == -1)
+	if (status == 1)
 		ksft_test_result_fail("unexpected PR_GET_MEMORY_MERGE result in child\n");
-	else if (status == -2)
+	else if (status == 2)
 		ksft_test_result_fail("Merge in child failed\n");
-	else if (status == -3)
+	else if (status == 3)
 		ksft_test_result_skip("Merge in child skipped\n");
+	else if (status == 4)
+		ksft_test_result_fail("Binary not found\n");
 }
 
 /* Verify that prctl ksm flag is inherited. */
@@ -548,6 +467,7 @@ static void test_prctl_fork(void)
 
 	child_pid = fork();
 	if (!child_pid) {
+		init_global_file_handles();
 		exit(test_child_ksm());
 	} else if (child_pid < 0) {
 		ksft_test_result_fail("fork() failed\n");
@@ -595,10 +515,10 @@ static void test_prctl_fork_exec(void)
 		return;
 	} else if (child_pid == 0) {
 		char *prg_name = "./ksm_functional_tests";
-		char *argv_for_program[] = { prg_name, FORK_EXEC_CHILD_PRG_NAME };
+		char *argv_for_program[] = { prg_name, FORK_EXEC_CHILD_PRG_NAME, NULL };
 
 		execv(prg_name, argv_for_program);
-		return;
+		exit(4);
 	}
 
 	if (waitpid(child_pid, &status, 0) > 0) {
@@ -644,6 +564,7 @@ static void test_prctl_unmerge(void)
 	ksft_test_result(!range_maps_duplicates(map, size),
 			 "Pages were unmerged\n");
 unmap:
+	ksm_stop();
 	munmap(map, size);
 }
 
@@ -677,6 +598,47 @@ static void test_prot_none(void)
 	ksft_test_result(!range_maps_duplicates(map, size),
 			 "Pages were unmerged\n");
 unmap:
+	ksm_stop();
+	munmap(map, size);
+}
+
+static void test_fork_ksm_merging_page_count(void)
+{
+	const unsigned int size = 2 * MiB;
+	char *map;
+	pid_t child_pid;
+	int status;
+
+	ksft_print_msg("[RUN] %s\n", __func__);
+
+	map = mmap_and_merge_range(0xcf, size, PROT_READ | PROT_WRITE, KSM_MERGE_MADVISE);
+	if (map == MAP_FAILED)
+		return;
+
+	child_pid = fork();
+	if (!child_pid) {
+		init_global_file_handles();
+		exit(ksm_get_self_merging_pages());
+	} else if (child_pid < 0) {
+		ksft_test_result_fail("fork() failed\n");
+		goto unmap;
+	}
+
+	if (waitpid(child_pid, &status, 0) < 0) {
+		ksft_test_result_fail("waitpid() failed\n");
+		goto unmap;
+	}
+
+	status = WEXITSTATUS(status);
+	if (status) {
+		ksft_test_result_fail("ksm_merging_page in child: %d\n", status);
+		goto unmap;
+	}
+
+	ksft_test_result_pass("ksm_merging_pages is not inherited after fork\n");
+
+unmap:
+	ksm_stop();
 	munmap(map, size);
 }
 
@@ -685,24 +647,20 @@ static void init_global_file_handles(void)
 	mem_fd = open("/proc/self/mem", O_RDWR);
 	if (mem_fd < 0)
 		ksft_exit_fail_msg("opening /proc/self/mem failed\n");
-	ksm_fd = open("/sys/kernel/mm/ksm/run", O_RDWR);
-	if (ksm_fd < 0)
-		ksft_exit_skip("open(\"/sys/kernel/mm/ksm/run\") failed\n");
-	ksm_full_scans_fd = open("/sys/kernel/mm/ksm/full_scans", O_RDONLY);
-	if (ksm_full_scans_fd < 0)
-		ksft_exit_skip("open(\"/sys/kernel/mm/ksm/full_scans\") failed\n");
+	if (ksm_stop() < 0)
+		ksft_exit_skip("accessing \"/sys/kernel/mm/ksm/run\") failed\n");
+	if (ksm_get_full_scans() < 0)
+		ksft_exit_skip("accessing \"/sys/kernel/mm/ksm/full_scans\") failed\n");
 	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
 	if (pagemap_fd < 0)
 		ksft_exit_skip("open(\"/proc/self/pagemap\") failed\n");
-	proc_self_ksm_stat_fd = open("/proc/self/ksm_stat", O_RDONLY);
-	proc_self_ksm_merging_pages_fd = open("/proc/self/ksm_merging_pages",
-						O_RDONLY);
-	ksm_use_zero_pages_fd = open("/sys/kernel/mm/ksm/use_zero_pages", O_RDWR);
+	if (ksm_get_self_merging_pages() < 0)
+		ksft_exit_skip("accessing \"/proc/self/ksm_merging_pages\") failed\n");
 }
 
 int main(int argc, char **argv)
 {
-	unsigned int tests = 8;
+	unsigned int tests = 9;
 	int err;
 
 	if (argc > 1 && !strcmp(argv[1], FORK_EXEC_CHILD_PRG_NAME)) {
@@ -734,6 +692,7 @@ int main(int argc, char **argv)
 	test_prctl_fork();
 	test_prctl_fork_exec();
 	test_prctl_unmerge();
+	test_fork_ksm_merging_page_count();
 
 	err = ksft_get_fail_cnt();
 	if (err)