[PATCH v2 00/17] selftests/mm: improve khugepaged coverage

[PATCH v2 00/17] selftests/mm: improve khugepaged coverage

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

mTHP collapse went in for 7.2 with no functional selftest coverage. Every
khugepaged collapse case is PMD-shaped, down to the detection: it reads
smaps AnonHugePages, which cannot see anything below the PMD order.

I am also reworking khugepaged's collapse mechanism, and that wants a suite
worth trusting before the mechanism changes underneath it. Nothing here
depends on the rework: everything passes on an unmodified kernel and
documents what khugepaged already does.

This version sits on top of Baolin's anon mTHP collapse selftests [1], now
in mm-new. His mthp_khugepaged context and per-order detection are what the
new cases need, so they go in there rather than bringing their own.

Four existing cases fail on the environment rather than on the kernel:

 - The collapse wait is a fixed three seconds, whatever a huge page costs
   to build. Scale it with the PMD size.

 - collapse_compound_extreme wants a 512M folio from the fault path. Skip
   it where the PMD is that large.

 - The page cache caps folio order below the PMD order where a PMD is 512M,
   so nothing can hold a PMD-sized page cache folio. Skip the shmem and
   file cases there.

 - The swap cases ask a best-effort MADV_PAGEOUT for an exact swap count.
   Ask again before calling it a failure.

This is why the suite now runs on arm64 with 64K pages.

Then the new coverage:

 - Folio-order helpers in vm_util, and folio_order_check to validate them
   against the kernel before any collapse test trusts them.

 - Four order-parameterized anon collapse cases, plus mixed sources by
   source order, at every supported order by default.

 - A shared-source write race: a co-sharer writing throughout a collapse
   and the collapsing side must not see each other's pages.

 - khugepaged_full_pass(), which steps the daemon one scan at a time
   through the sysfs wake path, and khugepaged_sync_check to hold it to
   exactly one attributed collapse per step.

 - khugepaged_race, racing faults, MADV_DONTNEED, pins, fork and mremap
   against collapse, checked by content and by KASAN and lockdep.

Tested on mm-new (8086604be973), with KASAN, lockdep, DEBUG_VM and
page_table_check, in 16G guests:

  x86-64 4K     190 pass, 1 skip, 0 fail
  arm64 64K     228 pass, 5 skip, 0 fail

The skips are structural: mixed sources declines at the smallest order, and
at 64K collapse_compound_extreme and the shmem components skip as above.

Changes since v1:

 - Rebased onto [1] (Baolin Wang), which this overlapped and which is in
   mm-new now, so this applies on top of it. This series' own -o mode is
   gone in favour of his context.
 - A plain ./khugepaged and ./khugepaged_race now run everything they can:
   every supported order, and every mode, occupancy and pressure axis.  The
   options only narrow that down (Mike Rapoport).
 - The fixes to existing cases come first, then the infrastructure and the
   new tests, each next to what it validates (Mike Rapoport).
 - The completion barrier helper comes before the tests that use it, so no
   case carries a throwaway implementation of it (Mike Rapoport).
 - Changelogs and comments rewritten to be read rather than parsed
   (Mike Rapoport).
 - One new patch: retry the swapout, which is what made
   collapse_max_ptes_swap flaky at 64K.
 - Dropped the swap-skip patch, an equivalent has landed
   (Alexander Gordeev).
 - Review fixes: masked failures, system state left behind on bail-out
   paths, arguments taken on trust (Sashiko).

[1] https://lore.kernel.org/all/cover.1785985999.git.baolin.wang@linux.alibaba.com

Kiryl Shutsemau (Meta) (17):
  selftests/mm: skip collapse_compound_extreme where the PMD is too
    large
  selftests/mm: scale khugepaged's collapse wait with the PMD size
  selftests/mm: skip khugepaged page cache cases without a PMD folio
  selftests/mm: retry the swapout the khugepaged swap cases rely on
  selftests/mm: move is_backed_by_folio() into vm_util
  selftests/mm: add folio-order check for address ranges
  selftests/mm: add folio-order detection self-check
  selftests/mm: add khugepaged completion barrier helper
  selftests/mm: add order-parameterized khugepaged collapse cases
  selftests/mm: parameterize the mixed-source collapse case by source
    order
  selftests/mm: cover a shared-source collapse write race
  selftests/mm: run every supported collapse order by default
  selftests/mm: verify synchronous khugepaged driving is attributable
  selftests/mm: add khugepaged race harness
  selftests/mm: race collapse of windows with holes
  selftests/mm: add memory-pressure threads to the khugepaged race
    harness
  selftests/mm: zap whole PTE tables in the khugepaged race harness

 tools/testing/selftests/mm/Makefile           |   3 +
 .../testing/selftests/mm/folio_order_check.c  | 137 +++++
 tools/testing/selftests/mm/hmm-tests.c        |   1 -
 .../testing/selftests/mm/hugepage_settings.c  |  72 ++-
 .../testing/selftests/mm/hugepage_settings.h  |   3 +
 tools/testing/selftests/mm/khugepaged.c       | 466 +++++++++++++-
 tools/testing/selftests/mm/khugepaged_race.c  | 571 ++++++++++++++++++
 .../selftests/mm/khugepaged_sync_check.c      | 217 +++++++
 tools/testing/selftests/mm/run_vmtests.sh     |   8 +-
 .../selftests/mm/split_huge_page_test.c       |  62 --
 tools/testing/selftests/mm/vm_util.c          | 145 +++++
 tools/testing/selftests/mm/vm_util.h          |  10 +
 12 files changed, 1599 insertions(+), 96 deletions(-)
 create mode 100644 tools/testing/selftests/mm/folio_order_check.c
 create mode 100644 tools/testing/selftests/mm/khugepaged_race.c
 create mode 100644 tools/testing/selftests/mm/khugepaged_sync_check.c


base-commit: 8086604be9733378461a5534c39cb72635226b23
-- 
2.54.0

[PATCH v2 01/17] selftests/mm: skip collapse_compound_extreme where the PMD is too large

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

collapse_compound_extreme builds a PTE table full of distinct PTE-mapped
compound pages by cycling hpage_pmd_nr fault-time THPs through mremap.  It
therefore needs hpage_pmd_nr PMD-order allocations in a row.  That is fine
at a 2M PMD (4K base pages) or a 32M one (16K), but a 512M PMD -- arm64
with 64K base pages -- makes each of those an order-13 allocation, which
the allocator cannot reliably hand out even once, let alone 8192 times.

The failure is not a quiet one: the case calls ksft_exit_fail_msg(), so the
whole binary stops and every case after it is lost.

Skip the case where the PMD is larger than 32M.  The MADV_COLLAPSE cases
still cover PMD-order collapse on those configurations, and 4K and 16K
PMDs are unaffected.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 9a90ff5f484e..51fc1f04d0a0 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1007,6 +1007,16 @@ static void collapse_compound_extreme(struct collapse_context *c, struct mem_ops
 	void *p;
 	int i;
 
+	/*
+	 * The test needs hpage_pmd_nr PMD-order allocations, which is likely to
+	 * fail for large PMD sizes.  Skip if the PMD size is over 32M.
+	 */
+	if (hpage_pmd_size > (32UL << 20)) {
+		ksft_test_result_skip("%s: PMD too large for fault-time THP construction\n",
+				      __func__);
+		return;
+	}
+
 	p = ops->setup_area(1);
 	ksft_print_msg("Construct PTE page table full of different PTE-mapped compound pages\n");
 	for (i = 0; i < hpage_pmd_nr; i++) {
-- 
2.54.0

[PATCH v2 02/17] selftests/mm: scale khugepaged's collapse wait with the PMD size

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

wait_for_scan() gives every case the same three seconds, whatever the huge
page costs to build.  collapse_full asks for four of them: 8M at a 2M PMD,
but 2G at a 512M PMD -- arm64 with 64K base pages.

Three seconds is thin at that size rather than generous.  Across 80 runs of
collapse_full on arm64 with 64K pages the wait was half a second in 73 of
them, with a tail to two seconds, and the case has timed out in a full
matrix run, reporting a failure for a collapse that was still going.

Keep three seconds as the floor and add a second per 128M to collapse.  A
2M PMD is unchanged.  A 512M PMD gets 19 seconds, which is headroom over
the observed tail rather than a measured requirement.  The budget bounds
how long a real failure takes to report, not how long a passing case
waits: wait_for_scan() returns as soon as the collapse turns up.

arm64/64K: khugepaged all:anon 21 pass/1 fail -> 22 pass/0 fail.  x86-64 is
unchanged.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 51fc1f04d0a0..0f828bfee31f 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -602,8 +602,10 @@ static bool wait_for_scan(const char *msg, char *p, size_t len,
 		int nr_hpages, int collap_order, struct mem_ops *ops)
 {
 	unsigned long hpage_size = page_size << collap_order;
+	/* Three seconds as a floor, plus a second per 128M to collapse */
+	const unsigned long bytes = (unsigned long)nr_hpages * hpage_size;
+	int timeout = 6 + 2 * (bytes / (128UL << 20));
 	int full_scans;
-	int timeout = 6; /* 3 seconds */
 
 	/* Sanity check */
 	if (!ops->check_huge(p, len, 0, hpage_size))
-- 
2.54.0

[PATCH v2 03/17] selftests/mm: skip khugepaged page cache cases without a PMD folio

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The page cache caps folio order at MAX_PAGECACHE_ORDER, which sits below
the PMD order where a PMD is 512M -- arm64 with 64K base pages.  A
PMD-sized page cache folio is then impossible, so MADV_COLLAPSE answers
-EINVAL and khugepaged passes over the range.  The shmem cases ask for one
anyway, so four of them fail and the run bails out in the middle.

The cap is one global, so it rules out every file mapping, not just shmem:
shmem_huge_global_enabled() drops the PMD order from what it allows, and
file_thp_enabled() refuses a regular file whose mapping cannot hold a PMD
folio.  Skip both mem types when the PMD order has no per-order
shmem_enabled control, which is the readable form of the cap: that control
is created for the orders in THP_ORDERS_ALL_FILE_DEFAULT.  A run left with
nothing to collapse into skips outright.

Anonymous collapse is unaffected: its orders are not capped this way.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 31 +++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 0f828bfee31f..9b1da0dd0f8e 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1424,6 +1424,37 @@ int main(int argc, char **argv)
 
 	setbuf(stdout, NULL);
 
+	/*
+	 * The page cache caps folio order at MAX_PAGECACHE_ORDER, which
+	 * xas_split_alloc() puts below the PMD order on arm64 with 64K pages.
+	 * A PMD-sized page cache folio is then impossible, so the kernel
+	 * refuses these collapses by design and there is nothing to test.
+	 *
+	 * The cap is one global, so it rules out every file mapping, not just
+	 * shmem: shmem_huge_global_enabled() drops the PMD order from what it
+	 * allows, and file_thp_enabled() refuses a regular file whose mapping
+	 * cannot hold a PMD folio.
+	 *
+	 * The per-order shmem_enabled control below is what makes the cap
+	 * readable: it is created for the orders in THP_ORDERS_ALL_FILE_DEFAULT,
+	 * which is the cap and nothing else, so whether the PMD order has one
+	 * answers for a regular file as much as for shmem.
+	 */
+	if (!(thp_shmem_supported_orders() & (1UL << hpage_pmd_order))) {
+		if (shmem_ops) {
+			ksft_print_msg("no PMD-order page cache folio: skipping shmem\n");
+			shmem_ops = NULL;
+		}
+		if (read_only_file_ops) {
+			ksft_print_msg("no PMD-order page cache folio: skipping file\n");
+			read_only_file_ops = NULL;
+			read_write_file_read_ops = NULL;
+			read_write_file_write_ops = NULL;
+		}
+		if (!anon_ops && !shmem_ops && !read_only_file_ops)
+			ksft_exit_skip("Nothing left to collapse into\n");
+	}
+
 	default_settings.khugepaged.max_ptes_none = hpage_pmd_nr - 1;
 	default_settings.khugepaged.max_ptes_swap = hpage_pmd_nr / 8;
 	default_settings.khugepaged.max_ptes_shared = hpage_pmd_nr / 2;
-- 
2.54.0

[PATCH v2 04/17] selftests/mm: retry the swapout the khugepaged swap cases rely on

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

collapse_max_ptes_swap() and collapse_swapin_single_pte() set their
precondition with MADV_PAGEOUT and then require smaps to report exactly the
range they asked for.  MADV_PAGEOUT is best effort: shrink_folio_list()
leaves a folio alone when it cannot reclaim it right away, and a folio
still under writeback from an earlier pageout is the common case.  The
count comes up short by a page or two, and the case fails on its
precondition without testing anything.

It shows on arm64 with 64K pages, where max_ptes_swap is 1024 pages: 64M of
swap per step, and the second step pages out folios the first step has only
just written back.  About one run in four ends in

  # Swapout 1024 of 8192 pages... Fail
  not ok 95 collapse_max_ptes_swap

A probe around the same two steps hits it on roughly one attempt in twenty,
and asking again 50ms later closes the gap within four tries.

Ask again for up to two seconds before reporting failure.  The wait costs
nothing when the first attempt is enough, which is the usual case.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 32 ++++++++++++++++++-------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 9b1da0dd0f8e..69e0fc4b12fb 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -241,6 +241,26 @@ static bool check_swap(void *addr, unsigned long size)
 	return swap;
 }
 
+/*
+ * MADV_PAGEOUT is best effort: shrink_folio_list() leaves a folio alone
+ * when it cannot reclaim it right away, and one still under writeback from
+ * an earlier pageout is the common case.  The swap count the caller asks
+ * for then arrives a moment later, so ask again before giving up.
+ */
+static bool swapout_range(void *p, unsigned long size)
+{
+	int i;
+
+	for (i = 0; i < 40; i++) {
+		if (madvise(p, size, MADV_PAGEOUT))
+			ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
+		if (check_swap(p, size))
+			return true;
+		usleep(50 * 1000);
+	}
+	return false;
+}
+
 static bool is_swap_available(unsigned long size)
 {
 	unsigned long swap_total = 0;
@@ -881,9 +901,7 @@ static void collapse_swapin_single_pte(struct collapse_context *c, struct mem_op
 	p = ops->setup_area(1);
 	ops->fault(p, 0, hpage_pmd_size);
 
-	if (madvise(p, page_size, MADV_PAGEOUT))
-		ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
-	if (check_swap(p, page_size)) {
+	if (swapout_range(p, page_size)) {
 		success("OK");
 	} else {
 		fail("Fail");
@@ -920,9 +938,7 @@ static void collapse_max_ptes_swap(struct collapse_context *c, struct mem_ops *o
 	p = ops->setup_area(1);
 	ops->fault(p, 0, hpage_pmd_size);
 
-	if (madvise(p, (max_ptes_swap + 1) * page_size, MADV_PAGEOUT))
-		ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
-	if (check_swap(p, (max_ptes_swap + 1) * page_size)) {
+	if (swapout_range(p, (max_ptes_swap + 1) * page_size)) {
 		success("OK");
 	} else {
 		fail("Fail");
@@ -937,9 +953,7 @@ static void collapse_max_ptes_swap(struct collapse_context *c, struct mem_ops *o
 		ops->fault(p, 0, hpage_pmd_size);
 		ksft_print_msg("Swapout %d of %d pages...", max_ptes_swap,
 		       hpage_pmd_nr);
-		if (madvise(p, max_ptes_swap * page_size, MADV_PAGEOUT))
-			ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
-		if (check_swap(p, max_ptes_swap * page_size)) {
+		if (swapout_range(p, max_ptes_swap * page_size)) {
 			success("OK");
 		} else {
 			fail("Fail");
-- 
2.54.0

[PATCH v2 05/17] selftests/mm: move is_backed_by_folio() into vm_util

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The khugepaged selftest is about to gain mTHP collapse coverage, which
needs to check that an address range is backed by a folio of a given
order.  split_huge_page_test.c already has the building block:
is_backed_by_folio() reads the compound head and tail flags from
/proc/kpageflags to classify the folio behind a page.

Move it into vm_util so other tests can use it.  No functional change.

Assisted-by: Claude-Code:claude-opus-5
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 .../selftests/mm/split_huge_page_test.c       | 62 -------------------
 tools/testing/selftests/mm/vm_util.c          | 62 +++++++++++++++++++
 tools/testing/selftests/mm/vm_util.h          |  2 +
 3 files changed, 64 insertions(+), 62 deletions(-)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 86a603692826..0adfe7dde7e5 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -42,68 +42,6 @@ const char *kpageflags_proc = "/proc/kpageflags";
 int pagemap_fd;
 int kpageflags_fd;
 
-static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
-		int kpageflags_fd)
-{
-	const uint64_t folio_head_flags = KPF_THP | KPF_COMPOUND_HEAD;
-	const uint64_t folio_tail_flags = KPF_THP | KPF_COMPOUND_TAIL;
-	const unsigned long nr_pages = 1UL << order;
-	unsigned long pfn_head;
-	uint64_t pfn_flags;
-	unsigned long pfn;
-	unsigned long i;
-
-	pfn = pagemap_get_pfn(pagemap_fd, vaddr);
-
-	/* non present page */
-	if (pfn == -1UL)
-		return false;
-
-	if (pageflags_get(pfn, kpageflags_fd, &pfn_flags))
-		goto fail;
-
-	/* check for order-0 pages */
-	if (!order) {
-		if (pfn_flags & (folio_head_flags | folio_tail_flags))
-			return false;
-		return true;
-	}
-
-	/* non THP folio */
-	if (!(pfn_flags & KPF_THP))
-		return false;
-
-	pfn_head = pfn & ~(nr_pages - 1);
-
-	if (pageflags_get(pfn_head, kpageflags_fd, &pfn_flags))
-		goto fail;
-
-	/* head PFN has no compound_head flag set */
-	if ((pfn_flags & folio_head_flags) != folio_head_flags)
-		return false;
-
-	/* check all tail PFN flags */
-	for (i = 1; i < nr_pages; i++) {
-		if (pageflags_get(pfn_head + i, kpageflags_fd, &pfn_flags))
-			goto fail;
-		if ((pfn_flags & folio_tail_flags) != folio_tail_flags)
-			return false;
-	}
-
-	/*
-	 * check the PFN after this folio, but if its flags cannot be obtained,
-	 * assume this folio has the expected order
-	 */
-	if (pageflags_get(pfn_head + nr_pages, kpageflags_fd, &pfn_flags))
-		return true;
-
-	/* If we find another tail page, then the folio is larger. */
-	return (pfn_flags & folio_tail_flags) != folio_tail_flags;
-fail:
-	ksft_exit_fail_msg("Failed to get folio info\n");
-	return false;
-}
-
 static int check_after_split_folio_orders(char *vaddr_start, size_t len,
 		int pagemap_fd, int kpageflags_fd, int orders[], int nr_orders)
 {
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 360c9ec6702b..3c276865a778 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -494,6 +494,68 @@ int pageflags_get(unsigned long pfn, int kpageflags_fd, uint64_t *flags)
 	return 0;
 }
 
+bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
+			int kpageflags_fd)
+{
+	const uint64_t folio_head_flags = KPF_THP | KPF_COMPOUND_HEAD;
+	const uint64_t folio_tail_flags = KPF_THP | KPF_COMPOUND_TAIL;
+	const unsigned long nr_pages = 1UL << order;
+	unsigned long pfn_head;
+	uint64_t pfn_flags;
+	unsigned long pfn;
+	unsigned long i;
+
+	pfn = pagemap_get_pfn(pagemap_fd, vaddr);
+
+	/* non present page */
+	if (pfn == -1UL)
+		return false;
+
+	if (pageflags_get(pfn, kpageflags_fd, &pfn_flags))
+		goto fail;
+
+	/* check for order-0 pages */
+	if (!order) {
+		if (pfn_flags & (folio_head_flags | folio_tail_flags))
+			return false;
+		return true;
+	}
+
+	/* non THP folio */
+	if (!(pfn_flags & KPF_THP))
+		return false;
+
+	pfn_head = pfn & ~(nr_pages - 1);
+
+	if (pageflags_get(pfn_head, kpageflags_fd, &pfn_flags))
+		goto fail;
+
+	/* head PFN has no compound_head flag set */
+	if ((pfn_flags & folio_head_flags) != folio_head_flags)
+		return false;
+
+	/* check all tail PFN flags */
+	for (i = 1; i < nr_pages; i++) {
+		if (pageflags_get(pfn_head + i, kpageflags_fd, &pfn_flags))
+			goto fail;
+		if ((pfn_flags & folio_tail_flags) != folio_tail_flags)
+			return false;
+	}
+
+	/*
+	 * check the PFN after this folio, but if its flags cannot be obtained,
+	 * assume this folio has the expected order
+	 */
+	if (pageflags_get(pfn_head + nr_pages, kpageflags_fd, &pfn_flags))
+		return true;
+
+	/* If we find another tail page, then the folio is larger. */
+	return (pfn_flags & folio_tail_flags) != folio_tail_flags;
+fail:
+	ksft_exit_fail_msg("Failed to get folio info\n");
+	return false;
+}
+
 /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
 int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
 			      bool miss, bool wp, bool minor, uint64_t *ioctls)
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 9a49af88702e..56a28ce7d029 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -97,6 +97,8 @@ int64_t allocate_transhuge(void *ptr, int pagemap_fd);
 int pageflags_get(unsigned long pfn, int kpageflags_fd, uint64_t *flags);
 int gather_folio_orders(char *vaddr_start, size_t len,
 		int pagemap_fd, int kpageflags_fd, int orders[], int nr_orders);
+bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
+			int kpageflags_fd);
 
 int uffd_register(int uffd, void *addr, uint64_t len,
 		  bool miss, bool wp, bool minor);
-- 
2.54.0

[PATCH v2 06/17] selftests/mm: add folio-order check for address ranges

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

An mTHP collapse test has to ask whether a range came out as folios of one
particular order, placed where a collapse would place them.  Nothing
answers that today: is_backed_by_folio() classifies the folio behind a
single page, and check_huge_anon() reads smaps AnonHugePages, which only
accounts PMD mappings.

Add is_range_backed_by_folio_orders().  For every order-aligned window of
the range it requires a present head PFN at its natural alignment and a
contiguous PFN run across the window.  A window stitched together from
several folios, or one holding a folio shifted off its natural position,
fails -- which is what makes the helper usable for "this window collapsed
and that one did not".

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/vm_util.c | 42 ++++++++++++++++++++++++++++
 tools/testing/selftests/mm/vm_util.h |  2 ++
 2 files changed, 44 insertions(+)

diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 3c276865a778..3f586f2c3d33 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -556,6 +556,48 @@ bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
 	return false;
 }
 
+/*
+ * Check whether every order-@order window of [start, len) maps exactly one
+ * folio of that order, head to tail.  The address range must be naturally
+ * aligned, each window's PFN run must be contiguous, and a window's first
+ * PFN must be the folio head.
+ *
+ * This is the check "did this range collapse into order-@order folios": a
+ * window assembled from parts of several folios, or mapping a folio shifted
+ * from its natural position, fails.
+ */
+bool is_range_backed_by_folio_orders(char *start, size_t len, int order,
+				     int pagemap_fd, int kpageflags_fd)
+{
+	const unsigned long nr_pages = 1UL << order;
+	const size_t window = nr_pages * psize();
+	char *vaddr;
+
+	if ((uintptr_t)start % window || len % window)
+		return false;
+
+	for (vaddr = start; vaddr < start + len; vaddr += window) {
+		unsigned long pfn = pagemap_get_pfn(pagemap_fd, vaddr);
+		unsigned long i;
+
+		/* Not present, or not mapping the folio head. */
+		if (pfn == -1UL || pfn % nr_pages)
+			return false;
+
+		for (i = 1; i < nr_pages; i++) {
+			if (pagemap_get_pfn(pagemap_fd, vaddr + i * psize()) !=
+			    pfn + i)
+				return false;
+		}
+
+		if (!is_backed_by_folio(vaddr, order, pagemap_fd,
+					kpageflags_fd))
+			return false;
+	}
+
+	return true;
+}
+
 /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
 int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
 			      bool miss, bool wp, bool minor, uint64_t *ioctls)
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 56a28ce7d029..39dfb18dc10c 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -99,6 +99,8 @@ int gather_folio_orders(char *vaddr_start, size_t len,
 		int pagemap_fd, int kpageflags_fd, int orders[], int nr_orders);
 bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
 			int kpageflags_fd);
+bool is_range_backed_by_folio_orders(char *start, size_t len, int order,
+				     int pagemap_fd, int kpageflags_fd);
 
 int uffd_register(int uffd, void *addr, uint64_t len,
 		  bool miss, bool wp, bool minor);
-- 
2.54.0

[PATCH v2 07/17] selftests/mm: add folio-order detection self-check

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The upcoming khugepaged mTHP tests detect collapse results with the
vm_util folio-order helpers instead of smaps AnonHugePages, which only
sees PMD mappings. Before any collapse test trusts those helpers, make
sure they agree with the kernel about what backs a mapping.

For every anon THP order the kernel supports, fault memory in with
only that order enabled and require the helpers to classify the
backing as exactly that order: not a neighbouring order, and 4K-backed
memory as order 0.

Runs in the thp category of run_vmtests.sh. Verified on x86-64 4K
(orders 0, 2-9) and arm64 64K (orders 0, 2-13).

While here: ALIGN() moves into vm_util.h, where the next test that needs a
round-up can find it, and hmm-tests.c drops its own copy.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/Makefile           |   1 +
 .../testing/selftests/mm/folio_order_check.c  | 137 ++++++++++++++++++
 tools/testing/selftests/mm/hmm-tests.c        |   1 -
 tools/testing/selftests/mm/run_vmtests.sh     |   2 +
 tools/testing/selftests/mm/vm_util.h          |   2 +
 5 files changed, 142 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/mm/folio_order_check.c

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 2d5366196e30..2093fcf6e915 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -104,6 +104,7 @@ TEST_GEN_FILES += guard-regions
 TEST_GEN_FILES += merge
 TEST_GEN_FILES += rmap
 TEST_GEN_FILES += folio_split_race_test
+TEST_GEN_FILES += folio_order_check
 
 ifneq ($(ARCH),arm64)
 TEST_GEN_FILES += soft-dirty
diff --git a/tools/testing/selftests/mm/folio_order_check.c b/tools/testing/selftests/mm/folio_order_check.c
new file mode 100644
index 000000000000..93030a42c3cc
--- /dev/null
+++ b/tools/testing/selftests/mm/folio_order_check.c
@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Self-check for the vm_util folio-order detection helpers,
+ * is_backed_by_folio() and is_range_backed_by_folio_orders().
+ *
+ * For every anon THP order the kernel supports, fault memory in with only
+ * that order enabled and verify the helpers report exactly that order:
+ * not a neighbouring order, and plain 4K memory as order 0. The helpers
+ * are what the khugepaged mTHP tests use to detect collapse results, so
+ * they must agree with the kernel's own idea of the backing before any
+ * collapse test relies on them.
+ */
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "kselftest.h"
+#include "vm_util.h"
+#include "hugepage_settings.h"
+
+static int pagemap_fd;
+static int kpageflags_fd;
+
+/* mmap an anon VMA of exactly @size bytes at a @size-aligned address. */
+static char *alloc_aligned(size_t size)
+{
+	size_t len = size * 2;
+	uintptr_t aligned;
+	char *p;
+
+	p = mmap(NULL, len, PROT_READ | PROT_WRITE,
+		 MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+	if (p == MAP_FAILED)
+		ksft_exit_fail_perror("mmap()");
+
+	aligned = ALIGN((uintptr_t)p, size);
+	if (aligned != (uintptr_t)p)
+		munmap(p, aligned - (uintptr_t)p);
+	if (aligned + size != (uintptr_t)p + len)
+		munmap((char *)aligned + size,
+		       (uintptr_t)p + len - aligned - size);
+
+	return (char *)aligned;
+}
+
+/*
+ * Enable only @order (order 0: nothing), fault one aligned window in and
+ * check the helpers see exactly @order.
+ */
+static void check_order(int order)
+{
+	struct thp_settings settings = *thp_current_settings();
+	size_t size = psize() << order;
+	bool ok = true;
+	char *p;
+	int i;
+
+	for (i = 0; i < NR_ORDERS; i++)
+		settings.hugepages[i].enabled = THP_NEVER;
+	if (order)
+		settings.hugepages[order].enabled = THP_ALWAYS;
+	thp_push_settings(&settings);
+
+	p = alloc_aligned(size);
+	*p = 1;
+
+	if (!is_range_backed_by_folio_orders(p, size, order,
+					     pagemap_fd, kpageflags_fd)) {
+		ksft_print_msg("order %d not detected after fault\n", order);
+		ok = false;
+	}
+
+	/* A lower order must be rejected: the folio is larger. */
+	if (order && is_range_backed_by_folio_orders(p, size, order - 1,
+						     pagemap_fd,
+						     kpageflags_fd)) {
+		ksft_print_msg("order %d also reported as order %d\n",
+			       order, order - 1);
+		ok = false;
+	}
+
+	/* Order 0 pages must not look like any large folio, and vice versa. */
+	if (order && is_range_backed_by_folio_orders(p, size, 0,
+						     pagemap_fd,
+						     kpageflags_fd)) {
+		ksft_print_msg("order %d also reported as order 0\n", order);
+		ok = false;
+	}
+
+	munmap(p, size);
+	thp_pop_settings();
+
+	ksft_test_result(ok, "order %d classified\n", order);
+}
+
+int main(void)
+{
+	struct thp_settings settings;
+	unsigned long orders;
+	int order;
+
+	ksft_print_header();
+
+	if (!thp_available())
+		ksft_exit_skip("Transparent Hugepages not available\n");
+
+	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+	if (pagemap_fd < 0)
+		ksft_exit_fail_perror("open(/proc/self/pagemap)");
+	kpageflags_fd = open("/proc/kpageflags", O_RDONLY);
+	if (kpageflags_fd < 0)
+		ksft_exit_skip("open(\"/proc/kpageflags\") requires root\n");
+
+	orders = thp_supported_orders();
+	if (!orders)
+		ksft_exit_skip("No supported THP orders\n");
+
+	ksft_set_plan(__builtin_popcountl(orders) + 1);
+
+	thp_save_settings();
+	thp_read_settings(&settings);
+	/* Base of the settings stack; the bottom entry is never popped. */
+	thp_push_settings(&settings);
+
+	check_order(0);
+	for (order = 1; order < NR_ORDERS; order++) {
+		if (!(orders & (1UL << order)))
+			continue;
+		check_order(order);
+	}
+
+
+	ksft_finished();
+}
diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
index e2642eca0d02..df426f9218e7 100644
--- a/tools/testing/selftests/mm/hmm-tests.c
+++ b/tools/testing/selftests/mm/hmm-tests.c
@@ -65,7 +65,6 @@ enum {
 #define HMM_PATH_MAX    64
 #define NTIMES		10
 
-#define ALIGN(x, a) (((x) + (a - 1)) & (~((a) - 1)))
 /* Just the flags we need, copied from mm.h: */
 
 #ifndef FOLL_WRITE
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index d09f9f6a384e..2652a7920b80 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -402,6 +402,8 @@ CATEGORY="pfnmap" run_test ./pfnmap
 # COW tests
 CATEGORY="cow" run_test ./cow
 
+CATEGORY="thp" run_test ./folio_order_check
+
 CATEGORY="thp" run_test ./khugepaged
 
 CATEGORY="thp" run_test ./khugepaged -s 2
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 39dfb18dc10c..ce05bce4670d 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -10,6 +10,8 @@
 #include <linux/fs.h>
 
 #define BIT_ULL(nr)                   (1ULL << (nr))
+#define ALIGN(x, a)                   (((x) + (a) - 1) & ~((a) - 1))
+
 #define PM_SOFT_DIRTY                 BIT_ULL(55)
 #define PM_MMAP_EXCLUSIVE             BIT_ULL(56)
 #define PM_UFFD_WP                    BIT_ULL(57)
-- 
2.54.0

[PATCH v2 08/17] selftests/mm: add khugepaged completion barrier helper

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

Race and functional tests need to drive khugepaged in step: set up a
layout, let one full scan pass over it, check the result.  The khugepaged
selftest already waits for full_scans to advance by two, but only makes
progress if scan_sleep_millisecs happens to be short.

Lift it into khugepaged_full_pass() and drive it through sysfs: any store
to scan_sleep_millisecs wakes the daemon, so the barrier completes
whatever the scan cadence.  It wakes once per missing pass -- over-waking
queues a straggler pass that overlaps what the caller sets up next.  One
wake completes one pass only if the whole mm list fits in a scan batch, so
callers need a large pages_to_scan.

Settings pushes must not start passes either, so thp_write_settings() now
writes a khugepaged knob only when its value changes.  That helper,
thp_update_num(), is exported for tests wanting the same restraint.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 .../testing/selftests/mm/hugepage_settings.c  | 72 ++++++++++++++++---
 .../testing/selftests/mm/hugepage_settings.h  |  3 +
 2 files changed, 66 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/mm/hugepage_settings.c b/tools/testing/selftests/mm/hugepage_settings.c
index d7917dce3aba..8afcdf9793bb 100644
--- a/tools/testing/selftests/mm/hugepage_settings.c
+++ b/tools/testing/selftests/mm/hugepage_settings.c
@@ -183,6 +183,17 @@ void thp_read_settings(struct thp_settings *settings)
 	}
 }
 
+/*
+ * Write only on change: any store to a khugepaged sysfs knob wakes the
+ * daemon, and settings pushes/pops must not start scan passes nobody
+ * asked for -- khugepaged_full_pass() is the only sanctioned wake.
+ */
+void thp_update_num(const char *name, unsigned long num)
+{
+	if (thp_read_num(name) != num)
+		thp_write_num(name, num);
+}
+
 void thp_write_settings(struct thp_settings *settings)
 {
 	struct khugepaged_settings *khugepaged = &settings->khugepaged;
@@ -198,15 +209,15 @@ void thp_write_settings(struct thp_settings *settings)
 			shmem_enabled_strings[settings->shmem_enabled]);
 	thp_write_num("use_zero_page", settings->use_zero_page);
 
-	thp_write_num("khugepaged/defrag", khugepaged->defrag);
-	thp_write_num("khugepaged/alloc_sleep_millisecs",
-			khugepaged->alloc_sleep_millisecs);
-	thp_write_num("khugepaged/scan_sleep_millisecs",
-			khugepaged->scan_sleep_millisecs);
-	thp_write_num("khugepaged/max_ptes_none", khugepaged->max_ptes_none);
-	thp_write_num("khugepaged/max_ptes_swap", khugepaged->max_ptes_swap);
-	thp_write_num("khugepaged/max_ptes_shared", khugepaged->max_ptes_shared);
-	thp_write_num("khugepaged/pages_to_scan", khugepaged->pages_to_scan);
+	thp_update_num("khugepaged/defrag", khugepaged->defrag);
+	thp_update_num("khugepaged/alloc_sleep_millisecs",
+		       khugepaged->alloc_sleep_millisecs);
+	thp_update_num("khugepaged/scan_sleep_millisecs",
+		       khugepaged->scan_sleep_millisecs);
+	thp_update_num("khugepaged/max_ptes_none", khugepaged->max_ptes_none);
+	thp_update_num("khugepaged/max_ptes_swap", khugepaged->max_ptes_swap);
+	thp_update_num("khugepaged/max_ptes_shared", khugepaged->max_ptes_shared);
+	thp_update_num("khugepaged/pages_to_scan", khugepaged->pages_to_scan);
 
 	if (dev_queue_read_ahead_path[0])
 		write_num(dev_queue_read_ahead_path, settings->read_ahead_kb);
@@ -230,6 +241,49 @@ void thp_write_settings(struct thp_settings *settings)
 	}
 }
 
+/*
+ * Completion barrier for khugepaged: wait until a full scan pass that
+ * started after this call has finished. full_scans must advance by two;
+ * a +1 step may complete a pass that examined this mm before the
+ * caller's setup was in place.
+ *
+ * Any store to scan_sleep_millisecs wakes the daemon, so the barrier works
+ * whatever the configured scan cadence -- but a store can be lost.
+ * __sleep_millisecs_store() clears khugepaged_sleep_expire and wakes the
+ * queue; if the daemon is between scans rather than sleeping, it sets
+ * khugepaged_sleep_expire itself on the way into khugepaged_wait_work() and
+ * then sleeps for the full interval, having never seen the store.  So keep
+ * storing until the pass lands; a store while the daemon is awake costs
+ * nothing and does not queue an extra pass.
+ *
+ * One wake completes one full pass only if the whole mm list fits in
+ * one scan batch, so callers must pair this with a large
+ * pages_to_scan.
+ */
+bool khugepaged_full_pass(unsigned int timeout_s)
+{
+	unsigned long deadline_ms = timeout_s * 1000UL;
+	unsigned long sleep_ms =
+		thp_read_num("khugepaged/scan_sleep_millisecs");
+	unsigned long elapsed_ms = 0;
+	int pass;
+
+	for (pass = 0; pass < 2; pass++) {
+		unsigned long target =
+			thp_read_num("khugepaged/full_scans") + 1;
+
+		while (thp_read_num("khugepaged/full_scans") < target) {
+			if (elapsed_ms >= deadline_ms)
+				return false;
+			thp_write_num("khugepaged/scan_sleep_millisecs",
+				      sleep_ms);
+			usleep(10 * 1000);
+			elapsed_ms += 10;
+		}
+	}
+	return true;
+}
+
 struct thp_settings *thp_current_settings(void)
 {
 	if (!settings_index) {
diff --git a/tools/testing/selftests/mm/hugepage_settings.h b/tools/testing/selftests/mm/hugepage_settings.h
index 726c73c43c05..ba7d38370d43 100644
--- a/tools/testing/selftests/mm/hugepage_settings.h
+++ b/tools/testing/selftests/mm/hugepage_settings.h
@@ -70,6 +70,7 @@ int thp_read_string(const char *name, const char * const strings[]);
 void thp_write_string(const char *name, const char *val);
 unsigned long thp_read_num(const char *name);
 void thp_write_num(const char *name, unsigned long num);
+void thp_update_num(const char *name, unsigned long num);
 
 void thp_write_settings(struct thp_settings *settings);
 void thp_read_settings(struct thp_settings *settings);
@@ -83,6 +84,8 @@ static inline void thp_save_settings(void)
 	hugepage_save_settings(/* thp = */ true, /* hugetlb = */ false);
 }
 
+bool khugepaged_full_pass(unsigned int timeout_s);
+
 void thp_set_read_ahead_path(char *path);
 unsigned long thp_supported_orders(void);
 unsigned long thp_shmem_supported_orders(void);
-- 
2.54.0

[PATCH v2 09/17] selftests/mm: add order-parameterized khugepaged collapse cases

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The mthp_khugepaged context runs the generic cases at a sub-PMD order,
which answers how many folios of that order a range ends up with.  It
cannot say which window they are in, so "the populated window collapsed
and its neighbour did not" and "one window collapsed twice" look alike.

Add four cases that check each aligned window on its own, with the
folio-order helpers in vm_util:

- collapse_order_single_window: only the populated window collapses;
- collapse_order_partial_window: the default max_ptes_none lets a window
  with one present PTE collapse;
- collapse_order_max_ptes_none: with max_ptes_none=0 a full window
  collapses and one missing a page does not;
- collapse_order_mixed_sources: sources that are already large folios of
  a smaller order collapse to the target.

Each case faults its region before MADV_HUGEPAGE with only the target
order enabled, so the sources are order 0 and the result can only come
from khugepaged.  They wait for a full pass rather than for the result to
appear: without a completed pass, "not collapsed" and "not scanned yet"
are the same thing.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 219 ++++++++++++++++++++++++
 1 file changed, 219 insertions(+)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 69e0fc4b12fb..bcaef17e430d 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -31,6 +31,8 @@ static unsigned long page_size;
 static int hpage_pmd_nr;
 static int anon_order;
 static int collapse_order;
+static int pagemap_fd = -1;
+static int kpageflags_fd = -1;
 
 #define PID_SMAPS "/proc/self/smaps"
 #define TEST_FILE "collapse_test_file"
@@ -1268,6 +1270,205 @@ static void madvise_retracted_page_tables(struct collapse_context *c,
 	ksft_test_result_report(exit_status, "%s\n", __func__);
 }
 
+/* Smallest order khugepaged will consider for mTHP collapse. */
+#define MIN_MTHP_ORDER 2
+
+/*
+ * Order-parameterized collapse cases for the mthp_khugepaged context.  What
+ * they add over the generic cases run under that context is per-window
+ * detection: which aligned window collapsed, and which of its neighbours did
+ * not.  check_huge() answers how many folios of the order the range holds,
+ * which cannot tell one window from another.
+ *
+ * The region is faulted before MADV_HUGEPAGE, and the target order is only
+ * enabled for madvise, so the sources are always order 0 and the collapse
+ * product can only have come from khugepaged.
+ */
+static size_t mthp_window_size(void)
+{
+	return page_size << collapse_order;
+}
+
+static void mthp_push_target_order(void)
+{
+	struct thp_settings settings = *thp_current_settings();
+	int i;
+
+	/*
+	 * The target order, for madvise only, and nothing else enabled: the
+	 * cases fault their region before MADV_HUGEPAGE, so the sources are
+	 * order 0 whatever -s asked the fault path for.  That matters for the
+	 * cases built around a hole -- a large source folio would fill it in
+	 * and the window would collapse after all.
+	 * collapse_order_mixed_sources enables the source order it wants on
+	 * top of this.
+	 */
+	settings.thp_enabled = THP_NEVER;
+	for (i = 0; i < NR_ORDERS; i++)
+		settings.hugepages[i].enabled = THP_NEVER;
+	settings.hugepages[collapse_order].enabled = THP_MADVISE;
+	thp_push_settings(&settings);
+}
+
+static bool window_collapsed(void *p, size_t len)
+{
+	return is_range_backed_by_folio_orders(p, len, collapse_order,
+					       pagemap_fd, kpageflags_fd);
+}
+
+/* No aligned window in [p, p + len) is backed at the target order. */
+static bool window_not_collapsed(void *p, size_t len)
+{
+	size_t window = mthp_window_size();
+	char *addr = p;
+
+	for (; len >= window; addr += window, len -= window) {
+		if (window_collapsed(addr, window))
+			return false;
+	}
+	return true;
+}
+
+static bool khugepaged_wait_full_pass(void)
+{
+	/* Wait up to 30 seconds for the pass to complete. */
+	return khugepaged_full_pass(30);
+}
+
+static void collapse_order_single_window(struct collapse_context *c,
+					 struct mem_ops *ops)
+{
+	size_t window = mthp_window_size();
+	void *p;
+
+	mthp_push_target_order();
+
+	p = ops->setup_area(1);
+	ops->fault(p, window, 2 * window);
+	if (!window_not_collapsed(p, hpage_pmd_size))
+		ksft_exit_fail_msg("Unexpected large folio after fault\n");
+
+	madvise(p, hpage_pmd_size, MADV_HUGEPAGE);
+	ksft_print_msg("Collapse one fully populated window...");
+	if (!khugepaged_wait_full_pass())
+		fail("Timeout");
+	else if (window_collapsed(p + window, window) &&
+		 window_not_collapsed(p, window) &&
+		 window_not_collapsed(p + 2 * window,
+				      hpage_pmd_size - 2 * window))
+		success("OK");
+	else
+		fail("Fail");
+
+	validate_memory(p, window, 2 * window);
+	ops->cleanup_area(p, hpage_pmd_size);
+	thp_pop_settings();
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
+static void collapse_order_partial_window(struct collapse_context *c,
+					  struct mem_ops *ops)
+{
+	void *p;
+
+	mthp_push_target_order();
+
+	p = ops->setup_area(1);
+	ops->fault(p, 0, page_size);
+	if (!window_not_collapsed(p, hpage_pmd_size))
+		ksft_exit_fail_msg("Unexpected large folio after fault\n");
+
+	madvise(p, hpage_pmd_size, MADV_HUGEPAGE);
+	ksft_print_msg("Collapse window with single PTE entry present...");
+	if (!khugepaged_wait_full_pass())
+		fail("Timeout");
+	else if (window_collapsed(p, mthp_window_size()))
+		success("OK");
+	else
+		fail("Fail");
+
+	validate_memory(p, 0, page_size);
+	ops->cleanup_area(p, hpage_pmd_size);
+	thp_pop_settings();
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
+static void collapse_order_max_ptes_none(struct collapse_context *c,
+					 struct mem_ops *ops)
+{
+	struct thp_settings settings;
+	size_t window = mthp_window_size();
+	void *p;
+
+	mthp_push_target_order();
+	settings = *thp_current_settings();
+	settings.khugepaged.max_ptes_none = 0;
+	thp_push_settings(&settings);
+
+	p = ops->setup_area(1);
+	ops->fault(p, 0, 2 * window - page_size);
+	if (!window_not_collapsed(p, hpage_pmd_size))
+		ksft_exit_fail_msg("Unexpected large folio after fault\n");
+
+	madvise(p, hpage_pmd_size, MADV_HUGEPAGE);
+	ksft_print_msg("Collapse full window, not the one missing a page...");
+	if (!khugepaged_wait_full_pass())
+		fail("Timeout");
+	else if (window_collapsed(p, window) &&
+		 window_not_collapsed(p + window, window))
+		success("OK");
+	else
+		fail("Fail");
+
+	validate_memory(p, 0, 2 * window - page_size);
+	ops->cleanup_area(p, hpage_pmd_size);
+	thp_pop_settings();
+	thp_pop_settings();
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
+static void collapse_order_mixed_sources(struct collapse_context *c,
+					 struct mem_ops *ops)
+{
+	struct thp_settings settings;
+	void *p;
+
+	if (collapse_order <= MIN_MTHP_ORDER) {
+		ksft_test_result_skip("%s: no source order below target\n",
+				      __func__);
+		return;
+	}
+
+	mthp_push_target_order();
+
+	/* Fault the whole region as order-MIN_MTHP_ORDER folios. */
+	settings = *thp_current_settings();
+	settings.hugepages[MIN_MTHP_ORDER].enabled = THP_ALWAYS;
+	thp_push_settings(&settings);
+	p = ops->setup_area(1);
+	ops->fault(p, 0, hpage_pmd_size);
+	thp_pop_settings();
+
+	if (!is_range_backed_by_folio_orders(p, hpage_pmd_size, MIN_MTHP_ORDER,
+					     pagemap_fd, kpageflags_fd))
+		ksft_exit_fail_msg("Region not backed by order-%d folios after fault\n",
+				   MIN_MTHP_ORDER);
+
+	madvise(p, hpage_pmd_size, MADV_HUGEPAGE);
+	ksft_print_msg("Collapse region backed by smaller large folios...");
+	if (!khugepaged_wait_full_pass())
+		fail("Timeout");
+	else if (window_collapsed(p, hpage_pmd_size))
+		success("OK");
+	else
+		fail("Fail");
+
+	validate_memory(p, 0, hpage_pmd_size);
+	ops->cleanup_area(p, hpage_pmd_size);
+	thp_pop_settings();
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
 static void usage(void)
 {
 	fprintf(stderr, "\nUsage: ./khugepaged [OPTIONS] <test type> [dir]\n\n");
@@ -1436,6 +1637,20 @@ int main(int argc, char **argv)
 
 	parse_test_type(argc, argv);
 
+	if (mthp_khugepaged_context &&
+	    !(thp_supported_orders() & (1UL << collapse_order)))
+		ksft_exit_skip("Order %d is not a supported anon THP order\n",
+			       collapse_order);
+
+	if (mthp_khugepaged_context) {
+		pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+		if (pagemap_fd < 0)
+			ksft_exit_fail_perror("open(/proc/self/pagemap)");
+		kpageflags_fd = open("/proc/kpageflags", O_RDONLY);
+		if (kpageflags_fd < 0)
+			ksft_exit_fail_perror("open(/proc/kpageflags)");
+	}
+
 	setbuf(stdout, NULL);
 
 	/*
@@ -1498,6 +1713,10 @@ int main(int argc, char **argv)
 	TEST(collapse_empty, madvise_context, anon_ops);
 
 	TEST(collapse_single_mthp, mthp_khugepaged_context, anon_ops);
+	TEST(collapse_order_single_window, mthp_khugepaged_context, anon_ops);
+	TEST(collapse_order_partial_window, mthp_khugepaged_context, anon_ops);
+	TEST(collapse_order_max_ptes_none, mthp_khugepaged_context, anon_ops);
+	TEST(collapse_order_mixed_sources, mthp_khugepaged_context, anon_ops);
 
 	TEST(collapse_single_pte_entry, khugepaged_context, anon_ops);
 	TEST(collapse_single_pte_entry, khugepaged_context, read_only_file_ops);
-- 
2.54.0

[PATCH v2 10/17] selftests/mm: parameterize the mixed-source collapse case by source order

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

collapse_order_mixed_sources faults its region as order-2 folios and
collapses them to the -c target.  Order 2 sits below the contpte threshold
on both arm64 page-size configurations, so nothing in this suite unfolds a
contpte source on purpose.

Let -s name the source order alongside -c, which was rejected before.  The
case then faults at that order, keeping order 2 when -s is absent, and the
source order has to be a supported mTHP order below the target.  Other
cases are unaffected: they enable their source order locally.

"-s 5 -c 7" on arm64/64K then collapses contpte-mapped sources into a
larger mTHP.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index bcaef17e430d..d3ff1b196e09 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1430,10 +1430,13 @@ static void collapse_order_max_ptes_none(struct collapse_context *c,
 static void collapse_order_mixed_sources(struct collapse_context *c,
 					 struct mem_ops *ops)
 {
+	int source_order = anon_order ? anon_order : MIN_MTHP_ORDER;
 	struct thp_settings settings;
 	void *p;
 
-	if (collapse_order <= MIN_MTHP_ORDER) {
+	/* Sources must be a supported mTHP order strictly below the target. */
+	if (source_order >= collapse_order ||
+	    !(thp_supported_orders() & (1UL << source_order))) {
 		ksft_test_result_skip("%s: no source order below target\n",
 				      __func__);
 		return;
@@ -1441,21 +1444,22 @@ static void collapse_order_mixed_sources(struct collapse_context *c,
 
 	mthp_push_target_order();
 
-	/* Fault the whole region as order-MIN_MTHP_ORDER folios. */
+	/* Fault the whole region as order-@source_order folios. */
 	settings = *thp_current_settings();
-	settings.hugepages[MIN_MTHP_ORDER].enabled = THP_ALWAYS;
+	settings.hugepages[source_order].enabled = THP_ALWAYS;
 	thp_push_settings(&settings);
 	p = ops->setup_area(1);
 	ops->fault(p, 0, hpage_pmd_size);
 	thp_pop_settings();
 
-	if (!is_range_backed_by_folio_orders(p, hpage_pmd_size, MIN_MTHP_ORDER,
+	if (!is_range_backed_by_folio_orders(p, hpage_pmd_size, source_order,
 					     pagemap_fd, kpageflags_fd))
 		ksft_exit_fail_msg("Region not backed by order-%d folios after fault\n",
-				   MIN_MTHP_ORDER);
+				   source_order);
 
 	madvise(p, hpage_pmd_size, MADV_HUGEPAGE);
-	ksft_print_msg("Collapse region backed by smaller large folios...");
+	ksft_print_msg("Collapse region backed by order-%d sources...",
+		       source_order);
 	if (!khugepaged_wait_full_pass())
 		fail("Timeout");
 	else if (window_collapsed(p, hpage_pmd_size))
@@ -1486,6 +1490,8 @@ static void usage(void)
 	fprintf(stderr,	"\t\t-s: mTHP size, expressed as page order.\n");
 	fprintf(stderr,	"\t\t    Defaults to 0. Use this size for anon or shmem allocations.\n");
 	fprintf(stderr,	"\t\t-c: collapse order for mTHP collapse, expressed as page order.\n");
+	fprintf(stderr,	"\t\t    With -s, -s names the mTHP source order for the\n");
+	fprintf(stderr,	"\t\t    mixed-source case (source order below the target).\n");
 	exit(1);
 }
 
-- 
2.54.0

[PATCH v2 11/17] selftests/mm: cover a shared-source collapse write race

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

collapse_fork checks that a fork-shared range collapses in the process
that asks for it while the co-sharer keeps its own page, but the co-sharer
sits still while that happens.

Add a case where the co-sharer writes to the shared range throughout the
collapse.  CoW has to keep the two sides apart under those writes: the
collapsing child must see the content from before the fork, and the
writing parent must see only its own writes.

It passes on an unmodified kernel, so it pins down isolation that
khugepaged collapse already provides.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 69 +++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index d3ff1b196e09..a5683f08694f 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1225,6 +1225,72 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
 	ksft_test_result_report(exit_status, "%s\n", __func__);
 }
 
+/*
+ * Content stays isolated while a co-sharer writes concurrently. A shared
+ * source is copied live (not frozen), relying on it being CoW - immutable
+ * for the duration of the copy; a co-sharer's write goes to a CoW copy. The
+ * collapsing child must see the pre-fork content, the writing parent only
+ * its own writes.
+ */
+static void collapse_fork_cow_race(struct collapse_context *c, struct mem_ops *ops)
+{
+	const unsigned long shared = 64 * page_size;
+	const int stride = page_size / sizeof(int);
+	int wstatus, child_status, i, n = shared / page_size;
+	/* volatile: the loop below must really store, on every iteration */
+	volatile int *ip;
+	void *p;
+
+	p = ops->setup_area(1);
+	ip = p;
+	ops->fault(p, 0, shared);		/* shared prefix, pre-fork pattern */
+
+	ksft_print_msg("Fork, collapse in the child while the parent rewrites...");
+	if (!fork()) {
+		int collapse_status;
+
+		ops->fault(p, shared, hpage_pmd_size);	/* private remainder */
+		c->collapse("Collapse a range shared with a writing co-sharer",
+			    p, 1, ops, true);
+		collapse_status = exit_status;
+		for (i = 0; i < n; i++)
+			if (ip[i * stride] != i + 0xdead0000)
+				break;
+		if (i == n)
+			success("OK");
+		else
+			fail("Fail: child content");
+		/* The content check must not bury a failed collapse. */
+		if (exit_status != KSFT_FAIL)
+			exit_status = collapse_status;
+		ops->cleanup_area(p, hpage_pmd_size);
+		_exit(exit_status);
+	}
+
+	/* Hammer the parent's own writes over the shared prefix. */
+	for (int it = 0; it < 200000; it++)
+		for (i = 0; i < n; i++)
+			ip[i * stride] = i + 0xbeef0000;
+
+	wait(&wstatus);
+	/* A child that died reading the racing pages is a failure, not a zero. */
+	child_status = WIFEXITED(wstatus) ? WEXITSTATUS(wstatus) : KSFT_FAIL;
+
+	ksft_print_msg("Check the parent sees only its own writes...");
+	for (i = 0; i < n; i++)
+		if (ip[i * stride] != i + 0xbeef0000)
+			break;
+	if (i == n)
+		success("OK");
+	else
+		fail("Fail: parent content");
+	ops->cleanup_area(p, hpage_pmd_size);
+	/* Same again: our own check must not bury the child's verdict. */
+	if (exit_status != KSFT_FAIL)
+		exit_status = child_status;
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
 static void madvise_collapse_existing_thps(struct collapse_context *c,
 					   struct mem_ops *ops)
 {
@@ -1778,6 +1844,9 @@ int main(int argc, char **argv)
 	TEST(collapse_max_ptes_shared, khugepaged_context, anon_ops);
 	TEST(collapse_max_ptes_shared, madvise_context, anon_ops);
 
+	TEST(collapse_fork_cow_race, khugepaged_context, anon_ops);
+	TEST(collapse_fork_cow_race, madvise_context, anon_ops);
+
 	TEST(madvise_collapse_existing_thps, madvise_context, anon_ops);
 	TEST(madvise_collapse_existing_thps, madvise_context, read_only_file_ops);
 	TEST(madvise_collapse_existing_thps, madvise_context, read_write_file_read_ops);
-- 
2.54.0

[PATCH v2 12/17] selftests/mm: run every supported collapse order by default

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The mTHP collapse cases only run when the caller names both the context
and an order, so a plain ./khugepaged covers the PMD contexts on anon and
nothing else.  run_vmtests.sh pinned order 4 and covered no other.

Without -c, run the mTHP cases once per supported anon THP order below the
PMD, and include that context in both the no-argument invocation and
"all".  -c still pins one order, and now says what is wrong when the order
is above the PMD or unsupported instead of printing the usage text.  An
order at or below the -s source order is skipped: the sources would
already be the size being asked for.

Both orders end up as array indices and shift counts, so -s rejects a
negative order and -c anything at or below 0, rather than letting either
reach them.

The mTHP context has only anon cases, so a run that names a different
mem_type -- "all:shmem", say -- drops it again rather than refusing to
start.  Naming both explicitly still does.

A case carries the order it was registered at, so a result names it:

  # Run test: collapse_order_max_ptes_none (mthp_khugepaged:anon, order 6)

On x86-64 with 4K pages that is orders 2 through 8, and ./khugepaged goes
from 28 results to 77 in 21 seconds, so run_vmtests.sh can drop its pinned
order-4 line.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c   | 111 ++++++++++++++++++----
 tools/testing/selftests/mm/run_vmtests.sh |   2 -
 2 files changed, 91 insertions(+), 22 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index a5683f08694f..a202fe359cf6 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -31,6 +31,9 @@ static unsigned long page_size;
 static int hpage_pmd_nr;
 static int anon_order;
 static int collapse_order;
+static bool collapse_order_given;
+static int collapse_orders[NR_ORDERS];
+static int nr_collapse_orders;
 static int pagemap_fd = -1;
 static int kpageflags_fd = -1;
 
@@ -1556,6 +1559,7 @@ static void usage(void)
 	fprintf(stderr,	"\t\t-s: mTHP size, expressed as page order.\n");
 	fprintf(stderr,	"\t\t    Defaults to 0. Use this size for anon or shmem allocations.\n");
 	fprintf(stderr,	"\t\t-c: collapse order for mTHP collapse, expressed as page order.\n");
+	fprintf(stderr,	"\t\t    Defaults to every supported order below the PMD.\n");
 	fprintf(stderr,	"\t\t    With -s, -s names the mTHP source order for the\n");
 	fprintf(stderr,	"\t\t    mixed-source case (source order below the target).\n");
 	exit(1);
@@ -1563,6 +1567,7 @@ static void usage(void)
 
 static void parse_test_type(int argc, char **argv)
 {
+	bool mthp_context_implied = false;
 	int opt;
 	char *buf;
 	const char *token;
@@ -1574,6 +1579,7 @@ static void parse_test_type(int argc, char **argv)
 			break;
 		case 'c':
 			collapse_order = atoi(optarg);
+			collapse_order_given = true;
 			break;
 		case 'h':
 		default:
@@ -1581,12 +1587,23 @@ static void parse_test_type(int argc, char **argv)
 		}
 	}
 
+	/*
+	 * Both orders end up as array indices and shift counts, so neither
+	 * can be negative, and a zero collapse order asks for base pages.
+	 */
+	if (anon_order < 0)
+		ksft_exit_fail_msg("-s takes an order, which cannot be negative\n");
+	if (collapse_order_given && collapse_order <= 0)
+		ksft_exit_fail_msg("-c takes an order above 0, not %d\n",
+				   collapse_order);
+
 	argv += optind;
 	argc -= optind;
 
 	if (argc == 0) {
-		/* Backwards compatibility */
+		/* Everything that needs no argument of its own: anon, every context */
 		khugepaged_context =  &__khugepaged_context;
+		mthp_khugepaged_context =  &__mthp_khugepaged_context;
 		madvise_context =  &__madvise_context;
 		anon_ops = &__anon_ops;
 		return;
@@ -1597,13 +1614,19 @@ static void parse_test_type(int argc, char **argv)
 
 	if (!strcmp(token, "all")) {
 		khugepaged_context =  &__khugepaged_context;
+		mthp_khugepaged_context =  &__mthp_khugepaged_context;
 		madvise_context =  &__madvise_context;
+
+		/*
+		 * "all" sweeps the mTHP context in, but it only has anon
+		 * cases: step it aside for the other mem_types rather than
+		 * refusing the whole run.
+		 */
+		mthp_context_implied = true;
 	} else if (!strcmp(token, "khugepaged")) {
 		khugepaged_context =  &__khugepaged_context;
 	} else if (!strcmp(token, "mthp_khugepaged")) {
 		mthp_khugepaged_context =  &__mthp_khugepaged_context;
-		if (collapse_order <= 0 || collapse_order >= hpage_pmd_order)
-			usage();
 	} else if (!strcmp(token, "madvise")) {
 		madvise_context =  &__madvise_context;
 	} else {
@@ -1619,20 +1642,20 @@ static void parse_test_type(int argc, char **argv)
 		read_write_file_write_ops =  &__read_write_file_write_ops;
 		anon_ops = &__anon_ops;
 		shmem_ops = &__shmem_ops;
-		if (mthp_khugepaged_context)
-			usage();
 	} else if (!strcmp(buf, "anon")) {
 		anon_ops = &__anon_ops;
 	} else if (!strcmp(buf, "file")) {
 		read_only_file_ops =  &__read_only_file_ops;
 		read_write_file_read_ops =  &__read_write_file_read_ops;
 		read_write_file_write_ops =  &__read_write_file_write_ops;
-		if (mthp_khugepaged_context)
+		if (mthp_khugepaged_context && !mthp_context_implied)
 			usage();
+		mthp_khugepaged_context = NULL;
 	} else if (!strcmp(buf, "shmem")) {
 		shmem_ops = &__shmem_ops;
-		if (mthp_khugepaged_context)
+		if (mthp_khugepaged_context && !mthp_context_implied)
 			usage();
+		mthp_khugepaged_context = NULL;
 	} else {
 		usage();
 	}
@@ -1654,9 +1677,14 @@ struct test_case {
 	struct mem_ops *ops;
 	const char *desc;
 	test_fn fn;
+	int order;		/* mTHP contexts: the collapse order */
 };
 
-#define MAX_TEST_CASES 64
+/*
+ * Enough for every case at every order the kernel offers: the mTHP context
+ * runs its cases once per supported order below the PMD.
+ */
+#define MAX_TEST_CASES 256
 static struct test_case test_cases[MAX_TEST_CASES];
 static int nr_test_cases;
 
@@ -1669,6 +1697,7 @@ static int nr_test_cases;
 			.ops	= o,					\
 			.desc	= #t,					\
 			.fn	= t,					\
+			.order	= collapse_order,			\
 		};							\
 	}								\
 	} while (0)
@@ -1709,10 +1738,40 @@ int main(int argc, char **argv)
 
 	parse_test_type(argc, argv);
 
-	if (mthp_khugepaged_context &&
-	    !(thp_supported_orders() & (1UL << collapse_order)))
-		ksft_exit_skip("Order %d is not a supported anon THP order\n",
-			       collapse_order);
+	if (mthp_khugepaged_context) {
+		unsigned long orders = thp_supported_orders();
+
+		if (collapse_order_given) {
+			/* -c pins one order; it has to be one we can build */
+			if (collapse_order >= hpage_pmd_order)
+				ksft_exit_fail_msg("-c takes an order below the PMD order (%d)\n",
+						   hpage_pmd_order);
+			if (!(orders & (1UL << collapse_order)))
+				ksft_exit_skip("Order %d is not a supported anon THP order\n",
+					       collapse_order);
+			if (collapse_order <= anon_order)
+				ksft_exit_skip("-c %d needs a source order below it, -s says %d\n",
+					       collapse_order, anon_order);
+			collapse_orders[nr_collapse_orders++] = collapse_order;
+		} else {
+			/*
+			 * Otherwise every order a collapse could produce.  -s
+			 * makes the fault path hand out folios of that order,
+			 * so a target at or below it has nothing to collapse:
+			 * the sources are already the size being asked for.
+			 */
+			int first = anon_order ? anon_order + 1 : MIN_MTHP_ORDER;
+
+			if (first < MIN_MTHP_ORDER)
+				first = MIN_MTHP_ORDER;
+			for (int i = first; i < hpage_pmd_order; i++) {
+				if (orders & (1UL << i))
+					collapse_orders[nr_collapse_orders++] = i;
+			}
+			if (!nr_collapse_orders)
+				ksft_print_msg("mTHP cases skipped: no order above the source\n");
+		}
+	}
 
 	if (mthp_khugepaged_context) {
 		pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
@@ -1773,7 +1832,17 @@ int main(int argc, char **argv)
 	TEST(collapse_full, khugepaged_context, read_write_file_read_ops);
 	TEST(collapse_full, khugepaged_context, read_write_file_write_ops);
 	TEST(collapse_full, khugepaged_context, shmem_ops);
-	TEST(collapse_full, mthp_khugepaged_context, anon_ops);
+	for (int i = 0; i < nr_collapse_orders; i++) {
+		collapse_order = collapse_orders[i];
+		TEST(collapse_full, mthp_khugepaged_context, anon_ops);
+		TEST(collapse_empty, mthp_khugepaged_context, anon_ops);
+		TEST(collapse_single_mthp, mthp_khugepaged_context, anon_ops);
+		TEST(collapse_order_single_window, mthp_khugepaged_context, anon_ops);
+		TEST(collapse_order_partial_window, mthp_khugepaged_context, anon_ops);
+		TEST(collapse_order_max_ptes_none, mthp_khugepaged_context, anon_ops);
+		TEST(collapse_order_mixed_sources, mthp_khugepaged_context, anon_ops);
+	}
+
 	TEST(collapse_full, madvise_context, anon_ops);
 	TEST(collapse_full, madvise_context, read_only_file_ops);
 	TEST(collapse_full, madvise_context, read_write_file_read_ops);
@@ -1781,14 +1850,8 @@ int main(int argc, char **argv)
 	TEST(collapse_full, madvise_context, shmem_ops);
 
 	TEST(collapse_empty, khugepaged_context, anon_ops);
-	TEST(collapse_empty, mthp_khugepaged_context, anon_ops);
 	TEST(collapse_empty, madvise_context, anon_ops);
 
-	TEST(collapse_single_mthp, mthp_khugepaged_context, anon_ops);
-	TEST(collapse_order_single_window, mthp_khugepaged_context, anon_ops);
-	TEST(collapse_order_partial_window, mthp_khugepaged_context, anon_ops);
-	TEST(collapse_order_max_ptes_none, mthp_khugepaged_context, anon_ops);
-	TEST(collapse_order_mixed_sources, mthp_khugepaged_context, anon_ops);
 
 	TEST(collapse_single_pte_entry, khugepaged_context, anon_ops);
 	TEST(collapse_single_pte_entry, khugepaged_context, read_only_file_ops);
@@ -1862,7 +1925,15 @@ int main(int argc, char **argv)
 	for (int i = 0; i < nr_test_cases; i++) {
 		struct test_case *t = &test_cases[i];
 
-		ksft_print_msg("\n# Run test: %s (%s:%s)\n", t->desc, t->ctx->name, t->ops->name);
+		if (t->ctx == &__mthp_khugepaged_context) {
+			collapse_order = t->order;
+			ksft_print_msg("\n# Run test: %s (%s:%s, order %d)\n",
+				       t->desc, t->ctx->name, t->ops->name,
+				       t->order);
+		} else {
+			ksft_print_msg("\n# Run test: %s (%s:%s)\n", t->desc,
+				       t->ctx->name, t->ops->name);
+		}
 		t->fn(t->ctx, t->ops);
 	}
 
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 2652a7920b80..8bf898b71350 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -412,8 +412,6 @@ CATEGORY="thp" run_test ./khugepaged all:shmem
 
 CATEGORY="thp" run_test ./khugepaged -s 4 all:shmem
 
-CATEGORY="thp" run_test ./khugepaged -c 4 mthp_khugepaged:anon
-
 # Try to create XFS if not provided
 if [ -z "${SPLIT_HUGE_PAGE_TEST_XFS_PATH}" ]; then
     if test_selected "thp"; then
-- 
2.54.0

[PATCH v2 13/17] selftests/mm: verify synchronous khugepaged driving is attributable

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The khugepaged tests attribute outcomes through the huge_memory
tracepoints.  The anon-path events carry no virtual address, but
mm_collapse_huge_page_isolate() reports a source folio PFN and order, and
the test matches those against the PFNs it read from pagemap before the
pass.  An attempt counts from whichever signal fires, so the check does
not depend on which anon tracepoint a kernel emits.

Add small tracefs helpers to vm_util and khugepaged_sync_check: per step,
prepare one aligned window, record its source PFNs, run one
khugepaged_full_pass() barrier, and require the window collapsed with
exactly one attributed attempt.  scan_sleep_millisecs is set high, so the
test only finishes in time if the sysfs store really wakes the daemon.

Passes 5/5 on x86-64 4K and arm64 64K.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/Makefile           |   1 +
 .../selftests/mm/khugepaged_sync_check.c      | 217 ++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh     |   2 +
 tools/testing/selftests/mm/vm_util.c          |  41 ++++
 tools/testing/selftests/mm/vm_util.h          |   4 +
 5 files changed, 265 insertions(+)
 create mode 100644 tools/testing/selftests/mm/khugepaged_sync_check.c

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 2093fcf6e915..b2d6e5c12934 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -105,6 +105,7 @@ TEST_GEN_FILES += merge
 TEST_GEN_FILES += rmap
 TEST_GEN_FILES += folio_split_race_test
 TEST_GEN_FILES += folio_order_check
+TEST_GEN_FILES += khugepaged_sync_check
 
 ifneq ($(ARCH),arm64)
 TEST_GEN_FILES += soft-dirty
diff --git a/tools/testing/selftests/mm/khugepaged_sync_check.c b/tools/testing/selftests/mm/khugepaged_sync_check.c
new file mode 100644
index 000000000000..30d3fb519fb2
--- /dev/null
+++ b/tools/testing/selftests/mm/khugepaged_sync_check.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Synchronous khugepaged driving check.
+ *
+ * Race tests drive khugepaged through the existing sysfs controls: a
+ * store to scan_sleep_millisecs wakes the daemon, and full_scans
+ * advancing by two is a completion barrier for one full pass that
+ * started after setup (khugepaged_full_pass()). Verify the pair gives
+ * deterministic, attributable results: one barrier step over one
+ * prepared window produces exactly one collapse attempt on that
+ * window's source pages (mm_collapse_huge_page_isolate events filtered
+ * by source PFN and order) and the window is collapsed
+ * afterwards, repeatably.
+ *
+ * scan_sleep_millisecs is set to 60s to prove the wake path: without
+ * the wake, one barrier step would sleep multiples of that and blow
+ * the timeout. It also keeps the daemon from free-running between
+ * steps, per the khugepaged_full_pass() discipline.
+ */
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "kselftest.h"
+#include "vm_util.h"
+#include "hugepage_settings.h"
+
+#define BASE_ADDR ((void *)(1UL << 30))
+#define TARGET_ORDER 2	/* smallest order khugepaged considers */
+#define NR_ITERATIONS 5
+
+static int pagemap_fd;
+static int kpageflags_fd;
+static int trace_events_fd = -1;
+static unsigned long hpage_pmd_size;
+
+/*
+ * Each step switches the events off again, but a helper can still give up
+ * on us in between (a failing sysfs write ends the test from inside
+ * thp_write_num()), and huge_memory events left on are the whole machine's
+ * problem, not this test's.
+ */
+static void trace_events_off(void)
+{
+	if (trace_events_fd >= 0)
+		tracing_events_enable(trace_events_fd, false);
+}
+
+/*
+ * Count collapse attempts attributable to our window: legacy-engine
+ * isolate events whose scan_pfn is one of the window's source PFNs,
+ * plus batch-engine per-candidate install events at the window's
+ * address. Either engine reports exactly once per attempt.
+ */
+static int count_attributed(unsigned long *pfns, int nr_pfns,
+			    unsigned long addr, unsigned int order)
+{
+	char line[1024];
+	int count = 0;
+	FILE *fp;
+
+	fp = tracing_open_trace();
+	if (!fp)
+		ksft_exit_fail_msg("Cannot open trace buffer\n");
+
+	while (fgets(line, sizeof(line), fp)) {
+		char *s;
+		unsigned long val;
+		unsigned int ord;
+		char *o;
+		int i;
+
+		s = strstr(line, "mm_collapse_huge_page_isolate:");
+		if (s) {
+			if (sscanf(s, "mm_collapse_huge_page_isolate: scan_pfn=0x%lx",
+				   &val) != 1)
+				continue;
+			o = strstr(s, "order=");
+			if (!o || sscanf(o, "order=%u", &ord) != 1 ||
+			    ord != order)
+				continue;
+			for (i = 0; i < nr_pfns; i++) {
+				if (val == pfns[i]) {
+					count++;
+					break;
+				}
+			}
+			continue;
+		}
+
+		s = strstr(line, "mm_collapse_candidate:");
+		if (s) {
+			if (!strstr(s, "pass=install") ||
+			    !strstr(s, "result=succeeded"))
+				continue;
+			o = strstr(s, "addr=");
+			if (!o || sscanf(o, "addr=0x%lx", &val) != 1 ||
+			    val != addr)
+				continue;
+			o = strstr(s, "order=");
+			if (!o || sscanf(o, "order=%u", &ord) != 1 ||
+			    ord != order)
+				continue;
+			count++;
+		}
+	}
+	fclose(fp);
+	return count;
+}
+
+static void one_step(int iteration)
+{
+	const size_t window = getpagesize() << TARGET_ORDER;
+	const int nr_pages = 1 << TARGET_ORDER;
+	unsigned long pfns[1 << TARGET_ORDER];
+	bool collapsed, passed;
+	int attributed;
+	char *p;
+	int i;
+
+	p = mmap(BASE_ADDR, hpage_pmd_size, PROT_READ | PROT_WRITE,
+		 MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE, -1, 0);
+	if (p != BASE_ADDR)
+		ksft_exit_fail_perror("mmap() window");
+
+	/* Prepare one window; record its source PFNs. */
+	for (i = 0; i < nr_pages; i++) {
+		p[i * getpagesize()] = i + 1;
+		pfns[i] = pagemap_get_pfn(pagemap_fd, p + i * getpagesize());
+		if (pfns[i] == -1UL)
+			ksft_exit_fail_msg("Source page not present\n");
+	}
+
+	/* Clear first: with the events still off there is nothing to undo. */
+	if (tracing_clear_trace())
+		ksft_exit_fail_msg("Cannot clear the trace buffer\n");
+	if (tracing_events_enable(trace_events_fd, true))
+		ksft_exit_fail_msg("Cannot enable huge_memory events\n");
+
+	madvise(p, hpage_pmd_size, MADV_HUGEPAGE);
+	/* Wait up to 120 seconds for the pass to complete. */
+	passed = khugepaged_full_pass(120);
+
+	/* Off before anything that can give up: the events are system-wide. */
+	if (tracing_events_enable(trace_events_fd, false))
+		ksft_exit_fail_msg("Cannot disable huge_memory events\n");
+	if (!passed)
+		ksft_exit_fail_msg("khugepaged did not complete a full pass\n");
+
+	collapsed = is_range_backed_by_folio_orders(p, window, TARGET_ORDER,
+						    pagemap_fd, kpageflags_fd);
+	attributed = count_attributed(pfns, nr_pages, (unsigned long)p,
+				      TARGET_ORDER);
+
+	ksft_test_result(collapsed && attributed == 1,
+			 "step %d: window collapsed, %d attributed result(s)\n",
+			 iteration, attributed);
+
+	munmap(p, hpage_pmd_size);
+}
+
+int main(void)
+{
+	struct thp_settings settings;
+	int i;
+
+	ksft_print_header();
+
+	if (!thp_available())
+		ksft_exit_skip("Transparent Hugepages not available\n");
+	if (!(thp_supported_orders() & (1UL << TARGET_ORDER)))
+		ksft_exit_skip("Order %d is not a supported anon THP order\n",
+			       TARGET_ORDER);
+
+	hpage_pmd_size = read_pmd_pagesize();
+	if (!hpage_pmd_size)
+		ksft_exit_fail_msg("Reading PMD pagesize failed\n");
+	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+	if (pagemap_fd < 0)
+		ksft_exit_fail_perror("open(/proc/self/pagemap)");
+	kpageflags_fd = open("/proc/kpageflags", O_RDONLY);
+	if (kpageflags_fd < 0)
+		ksft_exit_skip("open(\"/proc/kpageflags\") requires root\n");
+	trace_events_fd = tracing_events_open("huge_memory");
+	if (trace_events_fd < 0)
+		ksft_exit_skip("huge_memory events require tracefs and root\n");
+	atexit(trace_events_off);
+
+	ksft_set_plan(NR_ITERATIONS);
+
+	thp_save_settings();
+	thp_read_settings(&settings);
+	settings.thp_enabled = THP_MADVISE;
+	settings.thp_defrag = THP_DEFRAG_ALWAYS;
+	settings.khugepaged.defrag = 1;
+	settings.khugepaged.scan_sleep_millisecs = 60000;
+	settings.khugepaged.alloc_sleep_millisecs = 60000;
+	settings.khugepaged.max_ptes_none = (hpage_pmd_size / getpagesize()) - 1;
+	/* One wake must complete one full pass; see khugepaged_full_pass(). */
+	settings.khugepaged.pages_to_scan = 1UL << 24;
+	for (i = 0; i < NR_ORDERS; i++)
+		settings.hugepages[i].enabled = THP_NEVER;
+	settings.hugepages[TARGET_ORDER].enabled = THP_INHERIT;
+	/* Base of the settings stack; the bottom entry is never popped. */
+	thp_push_settings(&settings);
+
+	for (i = 0; i < NR_ITERATIONS; i++)
+		one_step(i);
+
+	thp_restore_settings();
+
+	ksft_finished();
+}
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 8bf898b71350..c0f69da3fd3b 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -404,6 +404,8 @@ CATEGORY="cow" run_test ./cow
 
 CATEGORY="thp" run_test ./folio_order_check
 
+CATEGORY="thp" run_test ./khugepaged_sync_check
+
 CATEGORY="thp" run_test ./khugepaged
 
 CATEGORY="thp" run_test ./khugepaged -s 2
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 3f586f2c3d33..3b2835279d37 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -598,6 +598,47 @@ bool is_range_backed_by_folio_orders(char *start, size_t len, int order,
 	return true;
 }
 
+#define TRACEFS_ROOT "/sys/kernel/tracing"
+
+/*
+ * Open the enable file of one ftrace event subsystem (e.g. "huge_memory").
+ * Returns a descriptor for tracing_events_enable(), or -1 if tracefs or the
+ * subsystem is not there.  The events are system-wide state: whoever
+ * switches them on owns them until it switches them off, including on the
+ * paths where the test gives up.
+ */
+int tracing_events_open(const char *subsys)
+{
+	char path[256];
+
+	snprintf(path, sizeof(path), TRACEFS_ROOT "/events/%s/enable",
+		 subsys);
+	return open(path, O_WRONLY);
+}
+
+int tracing_events_enable(int fd, bool enable)
+{
+	if (pwrite(fd, enable ? "1" : "0", 1, 0) != 1)
+		return -1;
+	return 0;
+}
+
+/* Drop what the trace buffer holds so far. */
+int tracing_clear_trace(void)
+{
+	int fd = open(TRACEFS_ROOT "/trace", O_WRONLY | O_TRUNC);
+
+	if (fd < 0)
+		return -1;
+	close(fd);
+	return 0;
+}
+
+FILE *tracing_open_trace(void)
+{
+	return fopen(TRACEFS_ROOT "/trace", "r");
+}
+
 /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
 int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
 			      bool miss, bool wp, bool minor, uint64_t *ioctls)
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index ce05bce4670d..10c7be46e44c 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -119,6 +119,10 @@ int close_procmap(struct procmap_fd *procmap);
 int write_sysfs(const char *file_path, unsigned long val);
 int read_sysfs(const char *file_path, unsigned long *val);
 bool softdirty_supported(void);
+int tracing_events_open(const char *subsys);
+int tracing_events_enable(int fd, bool enable);
+int tracing_clear_trace(void);
+FILE *tracing_open_trace(void);
 
 static inline int open_self_procmap(struct procmap_fd *procmap_out)
 {
-- 
2.54.0

[PATCH v2 14/17] selftests/mm: add khugepaged race harness

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

Collapse serialises against faults, GUP, fork, mremap and zapping through
a protocol of locks, TLB flushes and refcount checks.  No khugepaged
selftest exercises any of it under contention.

Add khugepaged_race.  Two faulters, an MADV_DONTNEED thread, a transient
FOLL_PIN thread (gup_test), a forker and an mremap thread work the same
ranges while one of three drivers collapses:

  stepped   khugepaged, one full pass at a time via
            khugepaged_full_pass(), so each step covers a known extent;
  free      khugepaged left to run (scan_sleep_millisecs=0), for soak;
  madvise   an MADV_COLLAPSE and MADV_DONTNEED loop.

Every mode runs in turn unless -m names one, five seconds each.  All anon
THP orders are enabled as inherit and max_ptes_none is 0, so a window
collapses only once fully populated and the racing MADV_DONTNEED steers
selection across orders.

The rule is that a racing page reads as its pattern or as zero, never
anything else.  The faulters and fork children check it throughout, and a
final sweep checks it again.  The kernel's own assertions -- DEBUG_VM,
page_table_check, KASAN, lockdep -- are the other half of the oracle, so
read dmesg too.

The threads share three PMD-sized areas plus one for the mremap thread;
-a sets the count, since at a 512M PMD the default is several gigabytes.
-d sets the soak length.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/Makefile          |   1 +
 tools/testing/selftests/mm/khugepaged_race.c | 410 +++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh    |   2 +
 3 files changed, 413 insertions(+)
 create mode 100644 tools/testing/selftests/mm/khugepaged_race.c

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index b2d6e5c12934..308bbad73c11 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -106,6 +106,7 @@ TEST_GEN_FILES += rmap
 TEST_GEN_FILES += folio_split_race_test
 TEST_GEN_FILES += folio_order_check
 TEST_GEN_FILES += khugepaged_sync_check
+TEST_GEN_FILES += khugepaged_race
 
 ifneq ($(ARCH),arm64)
 TEST_GEN_FILES += soft-dirty
diff --git a/tools/testing/selftests/mm/khugepaged_race.c b/tools/testing/selftests/mm/khugepaged_race.c
new file mode 100644
index 000000000000..3dc651dc56b3
--- /dev/null
+++ b/tools/testing/selftests/mm/khugepaged_race.c
@@ -0,0 +1,410 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * khugepaged race harness.
+ *
+ * Runs collapse against concurrent faults, transient GUP pins
+ * (gup_test), fork, mremap and MADV_DONTNEED over the same ranges, in
+ * one of three driver modes:
+ *
+ *   stepped	khugepaged, one full pass at a time through
+ *		khugepaged_full_pass(), so a step covers a known extent;
+ *   free	khugepaged left to run (scan_sleep_millisecs=0), for soak;
+ *   madvise	MADV_COLLAPSE in a loop.
+ *
+ * All anon THP orders are enabled (inherit) and max_ptes_none is 0, so a
+ * window has to be fully populated before khugepaged will collapse it, and
+ * the racing MADV_DONTNEED decides which orders it can still use.
+ *
+ * Correctness signals: every racing page must read as its pattern or
+ * zero (MADV_DONTNEED), never anything else.  The faulters and the fork
+ * children check that continuously, a final sweep checks it once more, plus
+ * whatever DEBUG_VM / page_table_check / KASAN / lockdep report in
+ * dmesg, which the caller is expected to inspect.
+ */
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/time.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "kselftest.h"
+#include "vm_util.h"
+#include "hugepage_settings.h"
+#include "../../../../mm/gup_test.h"
+
+#define BASE_ADDR	((void *)(1UL << 30))
+
+/*
+ * Shared playground for faults/pins/fork/dontneed: several PMD-sized
+ * areas the racing threads spread across, plus one area owned by the
+ * mremap thread. More areas means more independent regions collapsing
+ * at once; the default suits a normal machine. On a memory-constrained
+ * host -- or under emulation, where a 512M PMD (arm64/64K) makes the
+ * default playground multi-gigabyte -- pass -a to shrink it.
+ */
+#define DEFAULT_SHARED_AREAS	3
+static int nr_shared_areas;
+static int nr_areas;
+
+static unsigned long hpage_pmd_size;
+static unsigned long page_size;
+static char *region;		/* NR_AREAS * hpage_pmd_size */
+static char *mremap_area;	/* region + NR_SHARED_AREAS areas */
+static char *mremap_scratch;	/* well above the region */
+static int gup_fd = -1;
+static volatile int stop;
+static volatile int corrupted;
+
+static unsigned int pattern(unsigned long page_idx)
+{
+	unsigned int val = (unsigned int)page_idx * 2654435761U;
+
+	return val ? val : 1;	/* never collides with the zero-fill */
+}
+
+static void check_page(unsigned long page_idx)
+{
+	unsigned int val = *(unsigned int *)(region + page_idx * page_size);
+
+	if (val && val != pattern(page_idx)) {
+		corrupted = 1;
+		ksft_print_msg("Corruption at page %lu: %#x != %#x\n",
+			       page_idx, val, pattern(page_idx));
+	}
+}
+
+static unsigned long rand_page(unsigned int *seed)
+{
+	return (unsigned long)rand_r(seed) %
+	       (nr_shared_areas * hpage_pmd_size / page_size);
+}
+
+static void *faulter_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+
+	while (!stop) {
+		unsigned long page_idx = rand_page(&seed);
+
+		if (rand_r(&seed) & 1)
+			*(unsigned int *)(region + page_idx * page_size) =
+				pattern(page_idx);
+		else
+			check_page(page_idx);
+	}
+	return NULL;
+}
+
+static void *dontneed_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+
+	while (!stop) {
+		unsigned long page_idx = rand_page(&seed);
+		unsigned long nr = 1UL << (rand_r(&seed) % 6);	/* 1..32 pages */
+
+		madvise(region + page_idx * page_size, nr * page_size,
+			MADV_DONTNEED);
+		usleep(rand_r(&seed) % 500);
+	}
+	return NULL;
+}
+
+static void *pinner_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+
+	while (!stop) {
+		struct gup_test gup = {};
+		unsigned long page_idx = rand_page(&seed);
+
+		gup.addr = (unsigned long)(region + page_idx * page_size);
+		gup.size = 16 * page_size;
+		gup.nr_pages_per_call = 16;
+		gup.gup_flags = 1;	/* FOLL_WRITE */
+		/* Racing MADV_DONTNEED makes transient failures expected. */
+		ioctl(gup_fd, PIN_FAST_BENCHMARK, &gup);
+		usleep(rand_r(&seed) % 200);
+	}
+	return NULL;
+}
+
+static void *forker_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+
+	while (!stop) {
+		pid_t pid = fork();
+
+		if (pid == 0) {
+			for (int i = 0; i < 16; i++)
+				check_page(rand_page(&seed));
+			_exit(corrupted);
+		}
+		if (pid > 0) {
+			int wstatus;
+
+			if (waitpid(pid, &wstatus, 0) < 0)
+				ksft_exit_fail_perror("waitpid()");
+			/* A child killed on the read counts too, not just its exit code. */
+			if (!WIFEXITED(wstatus) || WEXITSTATUS(wstatus))
+				corrupted = 1;
+		}
+		usleep(rand_r(&seed) % 2000);
+	}
+	return NULL;
+}
+
+static void *mremapper_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+
+	while (!stop) {
+		void *p;
+
+		p = mremap(mremap_area, hpage_pmd_size, hpage_pmd_size,
+			   MREMAP_MAYMOVE | MREMAP_FIXED, mremap_scratch);
+		if (p == MAP_FAILED)
+			ksft_exit_fail_perror("mremap() away");
+		for (int i = 0; i < 8; i++)
+			mremap_scratch[(rand_r(&seed) %
+				(hpage_pmd_size / page_size)) * page_size] = 1;
+		p = mremap(mremap_scratch, hpage_pmd_size, hpage_pmd_size,
+			   MREMAP_MAYMOVE | MREMAP_FIXED, mremap_area);
+		if (p == MAP_FAILED)
+			ksft_exit_fail_perror("mremap() back");
+		usleep(rand_r(&seed) % 2000);
+	}
+	return NULL;
+}
+
+static unsigned long now_ms(void)
+{
+	struct timeval tv;
+
+	gettimeofday(&tv, NULL);
+	return tv.tv_sec * 1000UL + tv.tv_usec / 1000;
+}
+
+static void usage(void)
+{
+	fprintf(stderr,
+		"Usage: khugepaged_race [-d seconds] [-m stepped|free|madvise] [-a areas]\n"
+		"\tWithout -m, every mode runs in turn.\n"
+		"\t-d: seconds per mode (default 5)\n"
+		"\t-a: number of shared PMD-sized playground areas (default 3)\n");
+	exit(1);
+}
+
+int main(int argc, char **argv)
+{
+	static const char * const thread_names[] = {
+		"faulter", "faulter2", "dontneed", "pinner", "forker",
+		"mremapper",
+	};
+	void *(*const thread_fns[])(void *) = {
+		faulter_fn, faulter_fn, dontneed_fn, pinner_fn, forker_fn,
+		mremapper_fn,
+	};
+	const int nr_threads = ARRAY_SIZE(thread_names);
+	pthread_t threads[ARRAY_SIZE(thread_names)];
+	static const char * const all_modes[] = { "stepped", "free", "madvise" };
+	const char *one_mode[1];
+	const char * const *modes = all_modes;
+	int nr_modes = ARRAY_SIZE(all_modes);
+	const char *mode_arg = NULL;
+	struct thp_settings settings;
+	unsigned long end_ms;
+	int duration_s = 5;
+	unsigned long thread_mask = ~0UL;
+	int nr_areas_arg = 0;
+	unsigned long i;
+	int steps = 0;
+	int opt;
+
+	while ((opt = getopt(argc, argv, "a:d:m:t:h")) != -1) {
+		switch (opt) {
+		case 'a':
+			nr_areas_arg = atoi(optarg);
+			break;
+		case 'd':
+			duration_s = atoi(optarg);
+			break;
+		case 'm':
+			mode_arg = optarg;
+			break;
+		case 't':
+			/* debug: bitmask of racing threads to start */
+			thread_mask = strtoul(optarg, NULL, 0);
+			break;
+		default:
+			usage();
+		}
+	}
+	if (mode_arg) {
+		if (strcmp(mode_arg, "stepped") && strcmp(mode_arg, "free") &&
+		    strcmp(mode_arg, "madvise"))
+			usage();
+		one_mode[0] = mode_arg;
+		modes = one_mode;
+		nr_modes = 1;
+	}
+
+	ksft_print_header();
+	if (!thp_available())
+		ksft_exit_skip("Transparent Hugepages not available\n");
+
+	page_size = getpagesize();
+	hpage_pmd_size = read_pmd_pagesize();
+	if (!hpage_pmd_size)
+		ksft_exit_fail_msg("Reading PMD pagesize failed\n");
+
+	gup_fd = open("/sys/kernel/debug/gup_test", O_RDWR);
+	if (gup_fd < 0)
+		ksft_exit_skip("/sys/kernel/debug/gup_test requires CONFIG_GUP_TEST and root\n");
+
+	nr_shared_areas = nr_areas_arg > 0 ? nr_areas_arg : DEFAULT_SHARED_AREAS;
+	nr_areas = nr_shared_areas + 1;
+
+	/*
+	 * The mremap thread moves its area to this address and back, and
+	 * MREMAP_FIXED unmaps whatever is in the way without saying so.  Claim
+	 * the address here, so a layout that does not match this assumption
+	 * fails now instead of losing a mapping later.  Nothing else in the
+	 * process maps this low: thread stacks and malloc arenas come from the
+	 * top-down mmap area, well above.
+	 */
+	mremap_scratch = (char *)BASE_ADDR + 2 * nr_areas * hpage_pmd_size;
+	if (mmap(mremap_scratch, hpage_pmd_size, PROT_NONE,
+		 MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE,
+		 -1, 0) != (void *)mremap_scratch)
+		ksft_exit_fail_perror("mmap() mremap scratch");
+
+	ksft_set_plan(nr_modes);
+
+	thp_save_settings();
+	thp_read_settings(&settings);
+
+	/*
+	 * A base entry for the stack, so that the pop at the end of a mode
+	 * always has something to write back: thp_pop_settings() on an empty
+	 * stack has no settings to apply and gives up.
+	 */
+	thp_push_settings(&settings);
+
+	for (int m = 0; m < nr_modes; m++) {
+		const char *mode = modes[m];
+
+		thp_read_settings(&settings);
+		settings.thp_enabled = THP_MADVISE;
+		settings.thp_defrag = THP_DEFRAG_ALWAYS;
+		settings.shmem_enabled = SHMEM_NEVER;
+		settings.khugepaged.defrag = 1;
+		settings.khugepaged.scan_sleep_millisecs =
+			strcmp(mode, "free") ? 1000 : 0;
+		settings.khugepaged.alloc_sleep_millisecs = 10;
+		/*
+		 * Strict occupancy: mTHP collapse only supports 0 or
+		 * HPAGE_PMD_NR - 1 and coerces anything else to 0 anyway, and 0
+		 * also keeps khugepaged from burning the whole step in doomed
+		 * PMD-sized allocations on 512M-PMD configs: under racing
+		 * MADV_DONTNEED a fully populated PMD area is rare.
+		 */
+		settings.khugepaged.max_ptes_none = 0;
+		settings.khugepaged.pages_to_scan =
+			nr_areas * (hpage_pmd_size / page_size) * 8;
+		for (i = 0; i < NR_ORDERS; i++) {
+			if (thp_supported_orders() & (1UL << i))
+				settings.hugepages[i].enabled = THP_INHERIT;
+		}
+		/* Popped at the end of this mode, before the next one. */
+		thp_push_settings(&settings);
+
+		region = mmap(BASE_ADDR, nr_areas * hpage_pmd_size,
+			      PROT_READ | PROT_WRITE, MAP_ANONYMOUS |
+			      MAP_PRIVATE | MAP_FIXED_NOREPLACE, -1, 0);
+		if (region != BASE_ADDR)
+			ksft_exit_fail_perror("mmap() playground");
+		mremap_area = region + nr_shared_areas * hpage_pmd_size;
+
+		/* Populate so the first pass has something to collapse. */
+		for (i = 0; i < nr_shared_areas * hpage_pmd_size / page_size; i++)
+			*(unsigned int *)(region + i * page_size) = pattern(i);
+		memset(mremap_area, 1, hpage_pmd_size);
+		madvise(region, nr_areas * hpage_pmd_size, MADV_HUGEPAGE);
+
+		for (i = 0; i < nr_threads; i++) {
+			if (!(thread_mask & (1UL << i))) {
+				threads[i] = 0;
+				continue;
+			}
+			if (pthread_create(&threads[i], NULL, thread_fns[i],
+					   (void *)(i + 1)))
+				ksft_exit_fail_perror("pthread_create()");
+		}
+
+		end_ms = now_ms() + duration_s * 1000UL;
+		if (!strcmp(mode, "stepped")) {
+			while (now_ms() < end_ms && !corrupted) {
+				if (!khugepaged_full_pass(600))
+					ksft_exit_fail_msg("khugepaged pass timed out\n");
+				steps++;
+			}
+		} else if (!strcmp(mode, "free")) {
+			while (now_ms() < end_ms && !corrupted)
+				usleep(100 * 1000);
+		} else {	/* madvise */
+			while (now_ms() < end_ms && !corrupted) {
+				for (i = 0; i < nr_shared_areas; i++) {
+					madvise(region + i * hpage_pmd_size,
+						hpage_pmd_size, MADV_COLLAPSE);
+				}
+				madvise(region, nr_shared_areas * hpage_pmd_size,
+					MADV_DONTNEED);
+				steps++;
+			}
+		}
+
+		stop = 1;
+		for (i = 0; i < nr_threads; i++) {
+			if (threads[i])
+				pthread_join(threads[i], NULL);
+		}
+
+		/* Final integrity sweep. */
+		for (i = 0; i < nr_shared_areas * hpage_pmd_size / page_size; i++)
+			check_page(i);
+
+		ksft_test_result(!corrupted,
+				 "%s: %ds, %d steps, no corruption\n",
+				 mode, duration_s, steps);
+
+		/*
+		 * Hand the address space and the settings back before the
+		 * next mode: it maps the region at the same fixed address,
+		 * and its scan cadence differs.
+		 */
+		munmap(region, nr_areas * hpage_pmd_size);
+		thp_pop_settings();
+		stop = 0;
+		steps = 0;
+
+		if (corrupted) {
+			/* Memory is suspect; the rest would prove nothing. */
+			while (++m < nr_modes)
+				ksft_test_result_skip("%s: skipped after corruption\n",
+						      modes[m]);
+			break;
+		}
+	}
+
+	thp_restore_settings();
+	ksft_finished();
+}
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index c0f69da3fd3b..fc61907aa3b2 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -406,6 +406,8 @@ CATEGORY="thp" run_test ./folio_order_check
 
 CATEGORY="thp" run_test ./khugepaged_sync_check
 
+CATEGORY="thp" run_test ./khugepaged_race
+
 CATEGORY="thp" run_test ./khugepaged
 
 CATEGORY="thp" run_test ./khugepaged -s 2
-- 
2.54.0

[PATCH v2 15/17] selftests/mm: race collapse of windows with holes

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The harness pins max_ptes_none to 0, so khugepaged only collapses a window
once every PTE in it is present.  Collapsing a window that has holes never
happens, and that is a different path: a hole is not copied from anywhere
but zero-filled into the new folio, and the slot is re-checked under the
page table lock at install time in case a racing fault filled it first.

Run both ends of the occupancy scale, one after the other, for every
driver mode -- mTHP collapse supports only those two, 0 and
HPAGE_PMD_NR - 1, and coerces anything between them to 0.  Each result
says which end it ran:

  ok 1 stepped/strict: 5s, 231 steps, no corruption
  ok 2 stepped/holes: 5s, 194 steps, no corruption

-z narrows a run to the hole-heavy end, the way -m narrows it to one mode.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged_race.c | 57 +++++++++++++-------
 1 file changed, 39 insertions(+), 18 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged_race.c b/tools/testing/selftests/mm/khugepaged_race.c
index 3dc651dc56b3..a2a91906285b 100644
--- a/tools/testing/selftests/mm/khugepaged_race.c
+++ b/tools/testing/selftests/mm/khugepaged_race.c
@@ -11,9 +11,12 @@
  *   free	khugepaged left to run (scan_sleep_millisecs=0), for soak;
  *   madvise	MADV_COLLAPSE in a loop.
  *
- * All anon THP orders are enabled (inherit) and max_ptes_none is 0, so a
- * window has to be fully populated before khugepaged will collapse it, and
- * the racing MADV_DONTNEED decides which orders it can still use.
+ * All anon THP orders are enabled (inherit).  Occupancy runs at both ends
+ * of what mTHP collapse supports: max_ptes_none 0, where a window must be
+ * fully populated, and HPAGE_PMD_NR - 1, where a window full of holes
+ * collapses too.  The holes are not copied from anywhere -- they are
+ * zero-filled, and re-checked under the page table lock at install time in
+ * case a racing fault got there first.
  *
  * Correctness signals: every racing page must read as its pattern or
  * zero (MADV_DONTNEED), never anything else.  The faulters and the fork
@@ -196,9 +199,11 @@ static unsigned long now_ms(void)
 static void usage(void)
 {
 	fprintf(stderr,
-		"Usage: khugepaged_race [-d seconds] [-m stepped|free|madvise] [-a areas]\n"
+		"Usage: khugepaged_race [-d seconds] [-m stepped|free|madvise] [-z] [-a areas]\n"
 		"\tWithout -m, every mode runs in turn.\n"
 		"\t-d: seconds per mode (default 5)\n"
+		"\tBoth occupancy limits run unless -z asks for holes only.\n"
+		"\t-z: only max_ptes_none = HPAGE_PMD_NR - 1 (hole-heavy)\n"
 		"\t-a: number of shared PMD-sized playground areas (default 3)\n");
 	exit(1);
 }
@@ -216,6 +221,9 @@ int main(int argc, char **argv)
 	const int nr_threads = ARRAY_SIZE(thread_names);
 	pthread_t threads[ARRAY_SIZE(thread_names)];
 	static const char * const all_modes[] = { "stepped", "free", "madvise" };
+	static const int all_nones[] = { 0, 1 };	/* strict, holes */
+	const int *nones = all_nones;
+	int nr_nones = ARRAY_SIZE(all_nones);
 	const char *one_mode[1];
 	const char * const *modes = all_modes;
 	int nr_modes = ARRAY_SIZE(all_modes);
@@ -225,11 +233,12 @@ int main(int argc, char **argv)
 	int duration_s = 5;
 	unsigned long thread_mask = ~0UL;
 	int nr_areas_arg = 0;
+	bool holes_only = false;
 	unsigned long i;
 	int steps = 0;
 	int opt;
 
-	while ((opt = getopt(argc, argv, "a:d:m:t:h")) != -1) {
+	while ((opt = getopt(argc, argv, "a:d:m:t:zh")) != -1) {
 		switch (opt) {
 		case 'a':
 			nr_areas_arg = atoi(optarg);
@@ -244,10 +253,18 @@ int main(int argc, char **argv)
 			/* debug: bitmask of racing threads to start */
 			thread_mask = strtoul(optarg, NULL, 0);
 			break;
+		case 'z':
+			holes_only = true;
+			break;
 		default:
 			usage();
 		}
 	}
+	if (holes_only) {
+		nones = all_nones + 1;
+		nr_nones = 1;
+	}
+
 	if (mode_arg) {
 		if (strcmp(mode_arg, "stepped") && strcmp(mode_arg, "free") &&
 		    strcmp(mode_arg, "madvise"))
@@ -287,7 +304,7 @@ int main(int argc, char **argv)
 		 -1, 0) != (void *)mremap_scratch)
 		ksft_exit_fail_perror("mmap() mremap scratch");
 
-	ksft_set_plan(nr_modes);
+	ksft_set_plan(nr_modes * nr_nones);
 
 	thp_save_settings();
 	thp_read_settings(&settings);
@@ -299,8 +316,9 @@ int main(int argc, char **argv)
 	 */
 	thp_push_settings(&settings);
 
-	for (int m = 0; m < nr_modes; m++) {
-		const char *mode = modes[m];
+	for (int mn = 0; mn < nr_modes * nr_nones; mn++) {
+		const char *mode = modes[mn / nr_nones];
+		bool holes = nones[mn % nr_nones];
 
 		thp_read_settings(&settings);
 		settings.thp_enabled = THP_MADVISE;
@@ -310,14 +328,16 @@ int main(int argc, char **argv)
 		settings.khugepaged.scan_sleep_millisecs =
 			strcmp(mode, "free") ? 1000 : 0;
 		settings.khugepaged.alloc_sleep_millisecs = 10;
+
 		/*
-		 * Strict occupancy: mTHP collapse only supports 0 or
-		 * HPAGE_PMD_NR - 1 and coerces anything else to 0 anyway, and 0
-		 * also keeps khugepaged from burning the whole step in doomed
-		 * PMD-sized allocations on 512M-PMD configs: under racing
-		 * MADV_DONTNEED a fully populated PMD area is rare.
+		 * mTHP collapse only supports the two ends of the occupancy
+		 * scale: 0 or HPAGE_PMD_NR - 1 (anything else coerces to 0).
+		 * Strict needs a fully populated window, which is rare under
+		 * racing MADV_DONTNEED; hole-heavy windows collapse instead,
+		 * so the two ends race different paths.
 		 */
-		settings.khugepaged.max_ptes_none = 0;
+		settings.khugepaged.max_ptes_none = holes ?
+			(hpage_pmd_size / page_size) - 1 : 0;
 		settings.khugepaged.pages_to_scan =
 			nr_areas * (hpage_pmd_size / page_size) * 8;
 		for (i = 0; i < NR_ORDERS; i++) {
@@ -383,8 +403,9 @@ int main(int argc, char **argv)
 			check_page(i);
 
 		ksft_test_result(!corrupted,
-				 "%s: %ds, %d steps, no corruption\n",
-				 mode, duration_s, steps);
+				 "%s/%s: %ds, %d steps, no corruption\n",
+				 mode, holes ? "holes" : "strict",
+				 duration_s, steps);
 
 		/*
 		 * Hand the address space and the settings back before the
@@ -398,9 +419,9 @@ int main(int argc, char **argv)
 
 		if (corrupted) {
 			/* Memory is suspect; the rest would prove nothing. */
-			while (++m < nr_modes)
+			while (++mn < nr_modes * nr_nones)
 				ksft_test_result_skip("%s: skipped after corruption\n",
-						      modes[m]);
+						      modes[mn / nr_nones]);
 			break;
 		}
 	}
-- 
2.54.0

[PATCH v2 16/17] selftests/mm: add memory-pressure threads to the khugepaged race harness

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The harness races collapse against faults, pins, fork, mremap and
MADV_DONTNEED, but nothing in it elevates a source folio's refcount from
the reclaim or compaction side.

Add two more threads, and run every mode and occupancy limit both with and
without them:

 - pageout: cycles MADV_PAGEOUT over a dedicated neighbour region, faults
   it back in and checks the content each round, since a page's pattern
   must survive the trip through swap.  Idle when the host has no swap,
   because then there is no anon reclaim to drive.

 - compactor: writes /proc/sys/vm/compact_memory in a loop.  Compaction
   isolates and migrates folios, so it competes with a collapse for the
   pages it is gathering, with refcount elevations and migration entries
   of its own.

-p narrows a run to the combinations that have them, the way -z narrows
the occupancy and -m the mode.  Each result says which it ran:

  ok 2 stepped/strict/pressure: 5s, 88 steps, no corruption

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged_race.c | 147 +++++++++++++++++--
 1 file changed, 136 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged_race.c b/tools/testing/selftests/mm/khugepaged_race.c
index a2a91906285b..abd142db7cbe 100644
--- a/tools/testing/selftests/mm/khugepaged_race.c
+++ b/tools/testing/selftests/mm/khugepaged_race.c
@@ -18,6 +18,12 @@
  * zero-filled, and re-checked under the page table lock at install time in
  * case a racing fault got there first.
  *
+ * -p adds memory pressure to any of the above: MADV_PAGEOUT cycling
+ * on a dedicated neighbor region (swap traffic and LRU churn; skipped
+ * with a note when the host has no swap) and a compact_memory trigger
+ * loop (compaction migrates source folios, racing collapse's freeze
+ * with refcount elevation and migration entries of its own).
+ *
  * Correctness signals: every racing page must read as its pattern or
  * zero (MADV_DONTNEED), never anything else.  The faulters and the fork
  * children check that continuously, a final sweep checks it once more, plus
@@ -61,6 +67,8 @@ static unsigned long page_size;
 static char *region;		/* NR_AREAS * hpage_pmd_size */
 static char *mremap_area;	/* region + NR_SHARED_AREAS areas */
 static char *mremap_scratch;	/* well above the region */
+static char *pageout_area;	/* -p: dedicated pressure region */
+static size_t pageout_size;
 static int gup_fd = -1;
 static volatile int stop;
 static volatile int corrupted;
@@ -188,6 +196,70 @@ static void *mremapper_fn(void *arg)
 	return NULL;
 }
 
+/*
+ * -p: swap traffic and LRU churn on a region of our own. The content
+ * check is exact: a page out and back through swap must preserve the
+ * pattern, and nothing else ever writes here.
+ */
+static void *pageout_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+	unsigned long nr = pageout_size / page_size;
+	unsigned long i;
+
+	for (i = 0; i < nr; i++)
+		*(unsigned int *)(pageout_area + i * page_size) = pattern(i);
+
+	while (!stop) {
+		madvise(pageout_area, pageout_size, MADV_PAGEOUT);
+		for (i = 0; i < nr && !stop; i++) {
+			unsigned int val = *(unsigned int *)(pageout_area +
+							     i * page_size);
+
+			if (val != pattern(i)) {
+				corrupted = 1;
+				ksft_print_msg("Pageout corruption at page %lu: %#x != %#x\n",
+					       i, val, pattern(i));
+			}
+		}
+		usleep(rand_r(&seed) % 2000);
+	}
+	return NULL;
+}
+
+/* -p: compaction migrates the collapse sources out from under us. */
+static void *compactor_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+	int fd = open("/proc/sys/vm/compact_memory", O_WRONLY);
+
+	if (fd < 0) {
+		ksft_print_msg("No compact_memory; compactor idle\n");
+		return NULL;
+	}
+	while (!stop) {
+		if (write(fd, "1", 1) < 0)
+			break;
+		usleep(10000 + rand_r(&seed) % 100000);
+	}
+	close(fd);
+	return NULL;
+}
+
+static bool swap_available(void)
+{
+	char line[256];
+	int lines = 0;
+	FILE *fp = fopen("/proc/swaps", "r");
+
+	if (!fp)
+		return false;
+	while (fgets(line, sizeof(line), fp))
+		lines++;
+	fclose(fp);
+	return lines > 1;
+}
+
 static unsigned long now_ms(void)
 {
 	struct timeval tv;
@@ -199,11 +271,14 @@ static unsigned long now_ms(void)
 static void usage(void)
 {
 	fprintf(stderr,
-		"Usage: khugepaged_race [-d seconds] [-m stepped|free|madvise] [-z] [-a areas]\n"
+		"Usage: khugepaged_race [-d seconds] [-m stepped|free|madvise] [-z] [-p] [-a areas]\n"
 		"\tWithout -m, every mode runs in turn.\n"
 		"\t-d: seconds per mode (default 5)\n"
 		"\tBoth occupancy limits run unless -z asks for holes only.\n"
 		"\t-z: only max_ptes_none = HPAGE_PMD_NR - 1 (hole-heavy)\n"
+		"\tRuns with and without memory pressure unless -p asks for\n"
+		"\tpressure only.\n"
+		"\t-p: only with the pageout and compaction threads\n"
 		"\t-a: number of shared PMD-sized playground areas (default 3)\n");
 	exit(1);
 }
@@ -212,18 +287,22 @@ int main(int argc, char **argv)
 {
 	static const char * const thread_names[] = {
 		"faulter", "faulter2", "dontneed", "pinner", "forker",
-		"mremapper",
+		"mremapper", "pageout", "compactor",
 	};
 	void *(*const thread_fns[])(void *) = {
 		faulter_fn, faulter_fn, dontneed_fn, pinner_fn, forker_fn,
-		mremapper_fn,
+		mremapper_fn, pageout_fn, compactor_fn,
 	};
+	const unsigned long pageout_bit = 1UL << 6, compactor_bit = 1UL << 7;
 	const int nr_threads = ARRAY_SIZE(thread_names);
 	pthread_t threads[ARRAY_SIZE(thread_names)];
 	static const char * const all_modes[] = { "stepped", "free", "madvise" };
 	static const int all_nones[] = { 0, 1 };	/* strict, holes */
+	static const int all_press[] = { 0, 1 };	/* quiet, under pressure */
 	const int *nones = all_nones;
+	const int *press = all_press;
 	int nr_nones = ARRAY_SIZE(all_nones);
+	int nr_press = ARRAY_SIZE(all_press);
 	const char *one_mode[1];
 	const char * const *modes = all_modes;
 	int nr_modes = ARRAY_SIZE(all_modes);
@@ -232,13 +311,15 @@ int main(int argc, char **argv)
 	unsigned long end_ms;
 	int duration_s = 5;
 	unsigned long thread_mask = ~0UL;
+	unsigned long base_mask;
 	int nr_areas_arg = 0;
 	bool holes_only = false;
+	bool pressure_only = false;
 	unsigned long i;
 	int steps = 0;
 	int opt;
 
-	while ((opt = getopt(argc, argv, "a:d:m:t:zh")) != -1) {
+	while ((opt = getopt(argc, argv, "a:d:m:t:zph")) != -1) {
 		switch (opt) {
 		case 'a':
 			nr_areas_arg = atoi(optarg);
@@ -256,6 +337,9 @@ int main(int argc, char **argv)
 		case 'z':
 			holes_only = true;
 			break;
+		case 'p':
+			pressure_only = true;
+			break;
 		default:
 			usage();
 		}
@@ -265,6 +349,11 @@ int main(int argc, char **argv)
 		nr_nones = 1;
 	}
 
+	if (pressure_only) {
+		press = all_press + 1;
+		nr_press = 1;
+	}
+
 	if (mode_arg) {
 		if (strcmp(mode_arg, "stepped") && strcmp(mode_arg, "free") &&
 		    strcmp(mode_arg, "madvise"))
@@ -304,7 +393,12 @@ int main(int argc, char **argv)
 		 -1, 0) != (void *)mremap_scratch)
 		ksft_exit_fail_perror("mmap() mremap scratch");
 
-	ksft_set_plan(nr_modes * nr_nones);
+	base_mask = thread_mask;
+	if (!swap_available())
+		/* No swap, no anon reclaim: compaction-only pressure. */
+		ksft_print_msg("no swap: the pageout thread stays idle\n");
+
+	ksft_set_plan(nr_modes * nr_nones * nr_press);
 
 	thp_save_settings();
 	thp_read_settings(&settings);
@@ -316,9 +410,17 @@ int main(int argc, char **argv)
 	 */
 	thp_push_settings(&settings);
 
-	for (int mn = 0; mn < nr_modes * nr_nones; mn++) {
-		const char *mode = modes[mn / nr_nones];
-		bool holes = nones[mn % nr_nones];
+	for (int run = 0; run < nr_modes * nr_nones * nr_press; run++) {
+		int rem = run % (nr_nones * nr_press);
+		const char *mode = modes[run / (nr_nones * nr_press)];
+		bool holes = nones[rem / nr_press];
+		bool pressure = press[rem % nr_press];
+
+		thread_mask = base_mask;
+		if (!pressure)
+			thread_mask &= ~(pageout_bit | compactor_bit);
+		else if (!swap_available())
+			thread_mask &= ~pageout_bit;
 
 		thp_read_settings(&settings);
 		settings.thp_enabled = THP_MADVISE;
@@ -354,6 +456,24 @@ int main(int argc, char **argv)
 			ksft_exit_fail_perror("mmap() playground");
 		mremap_area = region + nr_shared_areas * hpage_pmd_size;
 
+		if (thread_mask & pageout_bit) {
+			/*
+			 * Big enough to cycle real reclaim, small enough not
+			 * to dominate a TCG guest: 4 PMD areas, clamped to
+			 * [16M, 64M].
+			 */
+			pageout_size = 4 * hpage_pmd_size;
+			pageout_size = pageout_size < (16UL << 20) ?
+				       (16UL << 20) :
+				       pageout_size > (64UL << 20) ?
+				       (64UL << 20) : pageout_size;
+			pageout_area = mmap(NULL, pageout_size,
+					    PROT_READ | PROT_WRITE,
+					    MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+			if (pageout_area == MAP_FAILED)
+				ksft_exit_fail_perror("mmap() pageout area");
+		}
+
 		/* Populate so the first pass has something to collapse. */
 		for (i = 0; i < nr_shared_areas * hpage_pmd_size / page_size; i++)
 			*(unsigned int *)(region + i * page_size) = pattern(i);
@@ -403,8 +523,9 @@ int main(int argc, char **argv)
 			check_page(i);
 
 		ksft_test_result(!corrupted,
-				 "%s/%s: %ds, %d steps, no corruption\n",
+				 "%s/%s%s: %ds, %d steps, no corruption\n",
 				 mode, holes ? "holes" : "strict",
+				 pressure ? "/pressure" : "",
 				 duration_s, steps);
 
 		/*
@@ -413,15 +534,19 @@ int main(int argc, char **argv)
 		 * and its scan cadence differs.
 		 */
 		munmap(region, nr_areas * hpage_pmd_size);
+		if (pageout_area) {
+			munmap(pageout_area, pageout_size);
+			pageout_area = NULL;
+		}
 		thp_pop_settings();
 		stop = 0;
 		steps = 0;
 
 		if (corrupted) {
 			/* Memory is suspect; the rest would prove nothing. */
-			while (++mn < nr_modes * nr_nones)
+			while (++run < nr_modes * nr_nones * nr_press)
 				ksft_test_result_skip("%s: skipped after corruption\n",
-						      modes[mn / nr_nones]);
+						      modes[run / (nr_nones * nr_press)]);
 			break;
 		}
 	}
-- 
2.54.0

[PATCH v2 17/17] selftests/mm: zap whole PTE tables in the khugepaged race harness

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The harness's MADV_DONTNEED thread zaps 1 to 32 pages at a time, never a
whole PMD-aligned area.  Empty-table reclaim (CONFIG_PT_RECLAIM) only
engages when a zap spans a full table, so no soak ever ran it against a
collapse -- fuzzing had to find that class instead: the page table
vanishing between the engine's park and install passes.

Make the thread zap a whole PMD-aligned area once every 64 iterations, and
keep the fine-grained zaps as the common case.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged_race.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged_race.c b/tools/testing/selftests/mm/khugepaged_race.c
index abd142db7cbe..1fbd20771a5a 100644
--- a/tools/testing/selftests/mm/khugepaged_race.c
+++ b/tools/testing/selftests/mm/khugepaged_race.c
@@ -121,8 +121,23 @@ static void *dontneed_fn(void *arg)
 		unsigned long page_idx = rand_page(&seed);
 		unsigned long nr = 1UL << (rand_r(&seed) % 6);	/* 1..32 pages */
 
-		madvise(region + page_idx * page_size, nr * page_size,
-			MADV_DONTNEED);
+		/*
+		 * Once in a while zap a whole PMD-aligned area: only a zap
+		 * spanning the full table triggers the empty-table reclaim
+		 * (CONFIG_PT_RECLAIM), which can free the table under a
+		 * collapse that is midway through it.  Sub-table zaps never
+		 * reach that path.
+		 */
+		if (!(rand_r(&seed) % 64)) {
+			unsigned long area = page_idx /
+					(hpage_pmd_size / page_size);
+
+			madvise(region + area * hpage_pmd_size,
+				hpage_pmd_size, MADV_DONTNEED);
+		} else {
+			madvise(region + page_idx * page_size,
+				nr * page_size, MADV_DONTNEED);
+		}
 		usleep(rand_r(&seed) % 500);
 	}
 	return NULL;
-- 
2.54.0

Re: [PATCH v2 00/17] selftests/mm: improve khugepaged coverage

[Alexander Gordeev]

On Fri, Aug 07, 2026 at 12:36:30PM +0100, Kiryl Shutsemau wrote:

Hi Kiryl,

...
>  - Dropped the swap-skip patch, an equivalent has landed
>    (Alexander Gordeev).

And dropped [1] following David feedback [2]. Would you pursue the proper fix?

1. https://lore.kernel.org/mm-commits/20260808063054.B75691F000E9@smtp.kernel.org/
2. https://lore.kernel.org/linux-mm/9d0d98ea-05bd-43c0-bb36-68aea62cbde8@kernel.org/

Thanks!

Re: [PATCH v2 00/17] selftests/mm: improve khugepaged coverage

[Muhammad Usama Anjum]

On 07/08/2026 12:36 pm, Kiryl Shutsemau wrote:
> From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
> 
> mTHP collapse went in for 7.2 with no functional selftest coverage. Every
> khugepaged collapse case is PMD-shaped, down to the detection: it reads
> smaps AnonHugePages, which cannot see anything below the PMD order.
> 
> I am also reworking khugepaged's collapse mechanism, and that wants a suite
> worth trusting before the mechanism changes underneath it. Nothing here
> depends on the rework: everything passes on an unmodified kernel and
> documents what khugepaged already does.
> 
> This version sits on top of Baolin's anon mTHP collapse selftests [1], now
> in mm-new. His mthp_khugepaged context and per-order detection are what the
> new cases need, so they go in there rather than bringing their own.
> 
> Four existing cases fail on the environment rather than on the kernel:
> 
>  - The collapse wait is a fixed three seconds, whatever a huge page costs
>    to build. Scale it with the PMD size.
> 
>  - collapse_compound_extreme wants a 512M folio from the fault path. Skip
>    it where the PMD is that large.
> 
>  - The page cache caps folio order below the PMD order where a PMD is 512M,
>    so nothing can hold a PMD-sized page cache folio. Skip the shmem and
>    file cases there.
> 
>  - The swap cases ask a best-effort MADV_PAGEOUT for an exact swap count.
>    Ask again before calling it a failure.
> 
> This is why the suite now runs on arm64 with 64K pages.
> 
> Then the new coverage:
> 
>  - Folio-order helpers in vm_util, and folio_order_check to validate them
>    against the kernel before any collapse test trusts them.
> 
>  - Four order-parameterized anon collapse cases, plus mixed sources by
>    source order, at every supported order by default.
> 
>  - A shared-source write race: a co-sharer writing throughout a collapse
>    and the collapsing side must not see each other's pages.
> 
>  - khugepaged_full_pass(), which steps the daemon one scan at a time
>    through the sysfs wake path, and khugepaged_sync_check to hold it to
>    exactly one attributed collapse per step.
> 
>  - khugepaged_race, racing faults, MADV_DONTNEED, pins, fork and mremap
>    against collapse, checked by content and by KASAN and lockdep.
> 
> Tested on mm-new (8086604be973), with KASAN, lockdep, DEBUG_VM and
> page_table_check, in 16G guests:
> 
>   x86-64 4K     190 pass, 1 skip, 0 fail
>   arm64 64K     228 pass, 5 skip, 0 fail
> 
> The skips are structural: mixed sources declines at the smallest order, and
> at 64K collapse_compound_extreme and the shmem components skip as above.
I've tested them on arm64 vm and more tests are passing instead of getting
skipped. Hence:

Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>

> 
> Changes since v1:
> 
>  - Rebased onto [1] (Baolin Wang), which this overlapped and which is in
>    mm-new now, so this applies on top of it. This series' own -o mode is
>    gone in favour of his context.
>  - A plain ./khugepaged and ./khugepaged_race now run everything they can:
>    every supported order, and every mode, occupancy and pressure axis.  The
>    options only narrow that down (Mike Rapoport).
>  - The fixes to existing cases come first, then the infrastructure and the
>    new tests, each next to what it validates (Mike Rapoport).
>  - The completion barrier helper comes before the tests that use it, so no
>    case carries a throwaway implementation of it (Mike Rapoport).
>  - Changelogs and comments rewritten to be read rather than parsed
>    (Mike Rapoport).
>  - One new patch: retry the swapout, which is what made
>    collapse_max_ptes_swap flaky at 64K.
>  - Dropped the swap-skip patch, an equivalent has landed
>    (Alexander Gordeev).
>  - Review fixes: masked failures, system state left behind on bail-out
>    paths, arguments taken on trust (Sashiko).
> 
> [1] https://lore.kernel.org/all/cover.1785985999.git.baolin.wang@linux.alibaba.com
> 
> Kiryl Shutsemau (Meta) (17):
>   selftests/mm: skip collapse_compound_extreme where the PMD is too
>     large
>   selftests/mm: scale khugepaged's collapse wait with the PMD size
>   selftests/mm: skip khugepaged page cache cases without a PMD folio
>   selftests/mm: retry the swapout the khugepaged swap cases rely on
>   selftests/mm: move is_backed_by_folio() into vm_util
>   selftests/mm: add folio-order check for address ranges
>   selftests/mm: add folio-order detection self-check
>   selftests/mm: add khugepaged completion barrier helper
>   selftests/mm: add order-parameterized khugepaged collapse cases
>   selftests/mm: parameterize the mixed-source collapse case by source
>     order
>   selftests/mm: cover a shared-source collapse write race
>   selftests/mm: run every supported collapse order by default
>   selftests/mm: verify synchronous khugepaged driving is attributable
>   selftests/mm: add khugepaged race harness
>   selftests/mm: race collapse of windows with holes
>   selftests/mm: add memory-pressure threads to the khugepaged race
>     harness
>   selftests/mm: zap whole PTE tables in the khugepaged race harness
> 
>  tools/testing/selftests/mm/Makefile           |   3 +
>  .../testing/selftests/mm/folio_order_check.c  | 137 +++++
>  tools/testing/selftests/mm/hmm-tests.c        |   1 -
>  .../testing/selftests/mm/hugepage_settings.c  |  72 ++-
>  .../testing/selftests/mm/hugepage_settings.h  |   3 +
>  tools/testing/selftests/mm/khugepaged.c       | 466 +++++++++++++-
>  tools/testing/selftests/mm/khugepaged_race.c  | 571 ++++++++++++++++++
>  .../selftests/mm/khugepaged_sync_check.c      | 217 +++++++
>  tools/testing/selftests/mm/run_vmtests.sh     |   8 +-
>  .../selftests/mm/split_huge_page_test.c       |  62 --
>  tools/testing/selftests/mm/vm_util.c          | 145 +++++
>  tools/testing/selftests/mm/vm_util.h          |  10 +
>  12 files changed, 1599 insertions(+), 96 deletions(-)
>  create mode 100644 tools/testing/selftests/mm/folio_order_check.c
>  create mode 100644 tools/testing/selftests/mm/khugepaged_race.c
>  create mode 100644 tools/testing/selftests/mm/khugepaged_sync_check.c
> 
> 
> base-commit: 8086604be9733378461a5534c39cb72635226b23

-- 
Thanks,
Usama

Re: [PATCH v2 00/17] selftests/mm: improve khugepaged coverage

[Kiryl Shutsemau]

On Mon, Aug 10, 2026 at 02:58:43PM +0200, Alexander Gordeev wrote:
> On Fri, Aug 07, 2026 at 12:36:30PM +0100, Kiryl Shutsemau wrote:
> 
> Hi Kiryl,
> 
> ...
> >  - Dropped the swap-skip patch, an equivalent has landed
> >    (Alexander Gordeev).
> 
> And dropped [1] following David feedback [2]. Would you pursue the proper fix?

Yes.  v3 will handle the failure rather than predict it.

is_swap_enabled() already skips these cases when no swap is active, so what
is left is swap that exists but cannot take what the case asks for.  The
series already has swapout_range(), which reissues MADV_PAGEOUT for up to two
seconds and reports whether the count arrived; I will make the two cases skip
when it does not.  That covers swap too small, swap full, a memcg limit and a
folio still under writeback, without reading /proc/meminfo for any of them.

An error from madvise() itself stays a hard failure -- that is the kernel
refusing, not the machine being short of swap.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCH v2 00/17] selftests/mm: improve khugepaged coverage

[Kiryl Shutsemau]

On Tue, Aug 11, 2026 at 12:40:51PM +0100, Muhammad Usama Anjum wrote:
> > Tested on mm-new (8086604be973), with KASAN, lockdep, DEBUG_VM and
> > page_table_check, in 16G guests:
> > 
> >   x86-64 4K     190 pass, 1 skip, 0 fail
> >   arm64 64K     228 pass, 5 skip, 0 fail
> > 
> > The skips are structural: mixed sources declines at the smallest order, and
> > at 64K collapse_compound_extreme and the shmem components skip as above.
> I've tested them on arm64 vm and more tests are passing instead of getting
> skipped. Hence:
> 
> Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>

Thanks!

-- 
  Kiryl Shutsemau / Kirill A. Shutemov