* [PATCH v3] selftests/mm: Add UFFDIO_MOVE huge zeropage PMD regression test
@ 2026-03-18 4:18 Chris Down
2026-03-19 15:42 ` Mike Rapoport
2026-03-19 19:34 ` David Hildenbrand (Arm)
0 siblings, 2 replies; 3+ messages in thread
From: Chris Down @ 2026-03-18 4:18 UTC (permalink / raw)
To: Andrew Morton
Cc: Mike Rapoport, Peter Xu, David Hildenbrand, Lorenzo Stoakes,
Liam R. Howlett, Vlastimil Babka, Suren Baghdasaryan,
Michal Hocko, Shuah Khan, Matthew Wilcox, kernel-team, linux-mm,
linux-kselftest, linux-kernel
The existing uffd-unit-tests move-pmd coverage exercises PMD-sized
UFFDIO_MOVE on anonymous THPs, but it does not force the huge zeropage
PMD path in move_pages_huge_pmd().
Add a dedicated anonymous UFFDIO_MOVE PMD test that exercises this
relatively comprehensively.
Signed-off-by: Chris Down <chris@chrisdown.name>
---
tools/testing/selftests/mm/uffd-unit-tests.c | 100 +++++++++++++++++++
tools/testing/selftests/mm/vm_util.c | 12 +++
tools/testing/selftests/mm/vm_util.h | 1 +
3 files changed, 113 insertions(+)
diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
index 6f5e404a446c..9cc4cbab9a23 100644
--- a/tools/testing/selftests/mm/uffd-unit-tests.c
+++ b/tools/testing/selftests/mm/uffd-unit-tests.c
@@ -1227,6 +1227,99 @@ static void uffd_move_pmd_test(uffd_global_test_opts_t *gopts, uffd_test_args_t
uffd_move_pmd_handle_fault);
}
+static void uffd_move_pmd_huge_zeropage_test(uffd_global_test_opts_t *gopts,
+ uffd_test_args_t *targs)
+{
+ unsigned long pmd_size = read_pmd_pagesize();
+ unsigned long pmd_pages;
+ unsigned long bytes = gopts->nr_pages * gopts->page_size;
+ char *orig_area_src = gopts->area_src, *orig_area_dst = gopts->area_dst;
+ char *aligned_src, *aligned_dst;
+ unsigned long src_offs, dst_offs, max_offs;
+ pthread_t uffd_mon;
+ struct uffd_args args = { 0 };
+ char c = '\0';
+ int pagemap_fd;
+
+ if (pmd_size <= gopts->page_size) {
+ uffd_test_skip("huge page size is 0, feature missing?");
+ return;
+ }
+ if (!detect_huge_zeropage()) {
+ uffd_test_skip("transparent huge zeropage disabled");
+ return;
+ }
+
+ pmd_pages = pmd_size / gopts->page_size;
+ if (bytes < pmd_size) {
+ uffd_test_skip("not enough pages for one PMD-sized move");
+ return;
+ }
+
+ aligned_src = ALIGN_UP(orig_area_src, pmd_size);
+ aligned_dst = ALIGN_UP(orig_area_dst, pmd_size);
+ src_offs = (aligned_src - orig_area_src) / gopts->page_size;
+ dst_offs = (aligned_dst - orig_area_dst) / gopts->page_size;
+ max_offs = src_offs > dst_offs ? src_offs : dst_offs;
+ if (max_offs + pmd_pages > gopts->nr_pages) {
+ uffd_test_skip("could not find aligned PMD-sized src/dst window");
+ return;
+ }
+
+ if (madvise(orig_area_dst, bytes, MADV_HUGEPAGE))
+ err("madvise(MADV_HUGEPAGE) failure");
+ if (madvise(orig_area_src, bytes, MADV_DONTFORK))
+ err("madvise(MADV_DONTFORK) failure");
+ if (madvise(aligned_src, pmd_size, MADV_DONTNEED))
+ err("madvise(MADV_DONTNEED) failure");
+
+ /* Fault in a PMD-sized huge zeropage mapping in the source. */
+ force_read_pages(aligned_src, pmd_pages, gopts->page_size);
+
+ pagemap_fd = pagemap_open();
+ if (!pagemap_is_huge_zero(pagemap_fd, aligned_src)) {
+ close(pagemap_fd);
+ uffd_test_skip("could not fault in the huge zeropage");
+ return;
+ }
+ gopts->area_src = aligned_src;
+ gopts->area_dst = aligned_dst;
+
+ if (uffd_register(gopts->uffd, gopts->area_dst, pmd_size, true, false, false))
+ err("register failure");
+
+ args.gopts = gopts;
+ args.handle_fault = uffd_move_pmd_handle_fault;
+ if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args))
+ err("uffd_poll_thread create");
+
+ /*
+ * One fault on dst should trigger a single PMD-sized UFFDIO_MOVE from
+ * the huge zeropage PMD we populated in the source.
+ */
+ force_read_pages(gopts->area_dst, pmd_pages, gopts->page_size);
+
+ if (write(gopts->pipefd[1], &c, sizeof(c)) != sizeof(c))
+ err("pipe write");
+ if (pthread_join(uffd_mon, NULL))
+ err("join() failed");
+
+ if (args.missing_faults != 1 || args.minor_faults != 0) {
+ uffd_test_fail("stats check error");
+ } else if (!pagemap_is_huge_zero(pagemap_fd, gopts->area_dst)) {
+ uffd_test_fail("moved destination is not a huge zeropage PMD");
+ } else if (!check_huge_anon(gopts->area_dst, 0, pmd_size)) {
+ /* vm_normal_page_pmd() must continue to treat the moved PMD as special. */
+ uffd_test_fail("moved huge zeropage PMD counted as AnonHugePages");
+ } else {
+ uffd_test_pass();
+ }
+
+ gopts->area_src = orig_area_src;
+ gopts->area_dst = orig_area_dst;
+ close(pagemap_fd);
+}
+
static void uffd_move_pmd_split_test(uffd_global_test_opts_t *gopts, uffd_test_args_t *targs)
{
if (madvise(gopts->area_dst, gopts->nr_pages * gopts->page_size, MADV_NOHUGEPAGE))
@@ -1550,6 +1643,13 @@ uffd_test_case_t uffd_tests[] = {
.uffd_feature_required = UFFD_FEATURE_MOVE,
.test_case_ops = &uffd_move_test_pmd_case_ops,
},
+ {
+ .name = "move-pmd-huge-zeropage",
+ .uffd_fn = uffd_move_pmd_huge_zeropage_test,
+ .mem_targets = MEM_ANON,
+ .uffd_feature_required = UFFD_FEATURE_MOVE,
+ .test_case_ops = &uffd_move_test_pmd_case_ops,
+ },
{
.name = "move-pmd-split",
.uffd_fn = uffd_move_pmd_split_test,
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index a6d4ff7dfdc0..55cc4cc058a2 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -120,6 +120,18 @@ bool pagemap_is_populated(int fd, char *start)
PAGE_IS_PRESENT | PAGE_IS_SWAPPED);
}
+bool pagemap_is_huge_zero(int fd, char *start)
+{
+ uint64_t categories;
+
+ if (!pagemap_scan_supported(fd, start))
+ return false;
+
+ categories = pagemap_scan_get_categories(fd, start);
+ return (categories & (PAGE_IS_PRESENT | PAGE_IS_PFNZERO | PAGE_IS_HUGE)) ==
+ (PAGE_IS_PRESENT | PAGE_IS_PFNZERO | PAGE_IS_HUGE);
+}
+
unsigned long pagemap_get_pfn(int fd, char *start)
{
uint64_t entry = pagemap_get_entry(fd, start);
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index e9c4e24769c1..e0b6ae1b12f5 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -85,6 +85,7 @@ uint64_t pagemap_get_entry(int fd, char *start);
bool pagemap_is_softdirty(int fd, char *start);
bool pagemap_is_swapped(int fd, char *start);
bool pagemap_is_populated(int fd, char *start);
+bool pagemap_is_huge_zero(int fd, char *start);
unsigned long pagemap_get_pfn(int fd, char *start);
void clear_softdirty(void);
bool check_for_pattern(FILE *fp, const char *pattern, char *buf, size_t len);
base-commit: f0caa1d49cc07b30a7e2f104d3853ec6dc1c3cad
--
2.53.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v3] selftests/mm: Add UFFDIO_MOVE huge zeropage PMD regression test
2026-03-18 4:18 [PATCH v3] selftests/mm: Add UFFDIO_MOVE huge zeropage PMD regression test Chris Down
@ 2026-03-19 15:42 ` Mike Rapoport
2026-03-19 19:34 ` David Hildenbrand (Arm)
1 sibling, 0 replies; 3+ messages in thread
From: Mike Rapoport @ 2026-03-19 15:42 UTC (permalink / raw)
To: Chris Down
Cc: Andrew Morton, Peter Xu, David Hildenbrand, Lorenzo Stoakes,
Liam R. Howlett, Vlastimil Babka, Suren Baghdasaryan,
Michal Hocko, Shuah Khan, Matthew Wilcox, kernel-team, linux-mm,
linux-kselftest, linux-kernel
On Wed, Mar 18, 2026 at 12:18:11PM +0800, Chris Down wrote:
> The existing uffd-unit-tests move-pmd coverage exercises PMD-sized
> UFFDIO_MOVE on anonymous THPs, but it does not force the huge zeropage
> PMD path in move_pages_huge_pmd().
>
> Add a dedicated anonymous UFFDIO_MOVE PMD test that exercises this
> relatively comprehensively.
>
> Signed-off-by: Chris Down <chris@chrisdown.name>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
> tools/testing/selftests/mm/uffd-unit-tests.c | 100 +++++++++++++++++++
> tools/testing/selftests/mm/vm_util.c | 12 +++
> tools/testing/selftests/mm/vm_util.h | 1 +
> 3 files changed, 113 insertions(+)
>
> diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
> index 6f5e404a446c..9cc4cbab9a23 100644
> --- a/tools/testing/selftests/mm/uffd-unit-tests.c
> +++ b/tools/testing/selftests/mm/uffd-unit-tests.c
> @@ -1227,6 +1227,99 @@ static void uffd_move_pmd_test(uffd_global_test_opts_t *gopts, uffd_test_args_t
> uffd_move_pmd_handle_fault);
> }
>
> +static void uffd_move_pmd_huge_zeropage_test(uffd_global_test_opts_t *gopts,
> + uffd_test_args_t *targs)
> +{
> + unsigned long pmd_size = read_pmd_pagesize();
> + unsigned long pmd_pages;
> + unsigned long bytes = gopts->nr_pages * gopts->page_size;
> + char *orig_area_src = gopts->area_src, *orig_area_dst = gopts->area_dst;
> + char *aligned_src, *aligned_dst;
> + unsigned long src_offs, dst_offs, max_offs;
> + pthread_t uffd_mon;
> + struct uffd_args args = { 0 };
> + char c = '\0';
> + int pagemap_fd;
> +
> + if (pmd_size <= gopts->page_size) {
> + uffd_test_skip("huge page size is 0, feature missing?");
> + return;
> + }
> + if (!detect_huge_zeropage()) {
> + uffd_test_skip("transparent huge zeropage disabled");
> + return;
> + }
> +
> + pmd_pages = pmd_size / gopts->page_size;
> + if (bytes < pmd_size) {
> + uffd_test_skip("not enough pages for one PMD-sized move");
> + return;
> + }
> +
> + aligned_src = ALIGN_UP(orig_area_src, pmd_size);
> + aligned_dst = ALIGN_UP(orig_area_dst, pmd_size);
> + src_offs = (aligned_src - orig_area_src) / gopts->page_size;
> + dst_offs = (aligned_dst - orig_area_dst) / gopts->page_size;
> + max_offs = src_offs > dst_offs ? src_offs : dst_offs;
> + if (max_offs + pmd_pages > gopts->nr_pages) {
> + uffd_test_skip("could not find aligned PMD-sized src/dst window");
> + return;
> + }
> +
> + if (madvise(orig_area_dst, bytes, MADV_HUGEPAGE))
> + err("madvise(MADV_HUGEPAGE) failure");
> + if (madvise(orig_area_src, bytes, MADV_DONTFORK))
> + err("madvise(MADV_DONTFORK) failure");
> + if (madvise(aligned_src, pmd_size, MADV_DONTNEED))
> + err("madvise(MADV_DONTNEED) failure");
> +
> + /* Fault in a PMD-sized huge zeropage mapping in the source. */
> + force_read_pages(aligned_src, pmd_pages, gopts->page_size);
> +
> + pagemap_fd = pagemap_open();
> + if (!pagemap_is_huge_zero(pagemap_fd, aligned_src)) {
> + close(pagemap_fd);
> + uffd_test_skip("could not fault in the huge zeropage");
> + return;
> + }
> + gopts->area_src = aligned_src;
> + gopts->area_dst = aligned_dst;
> +
> + if (uffd_register(gopts->uffd, gopts->area_dst, pmd_size, true, false, false))
> + err("register failure");
> +
> + args.gopts = gopts;
> + args.handle_fault = uffd_move_pmd_handle_fault;
> + if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args))
> + err("uffd_poll_thread create");
> +
> + /*
> + * One fault on dst should trigger a single PMD-sized UFFDIO_MOVE from
> + * the huge zeropage PMD we populated in the source.
> + */
> + force_read_pages(gopts->area_dst, pmd_pages, gopts->page_size);
> +
> + if (write(gopts->pipefd[1], &c, sizeof(c)) != sizeof(c))
> + err("pipe write");
> + if (pthread_join(uffd_mon, NULL))
> + err("join() failed");
> +
> + if (args.missing_faults != 1 || args.minor_faults != 0) {
> + uffd_test_fail("stats check error");
> + } else if (!pagemap_is_huge_zero(pagemap_fd, gopts->area_dst)) {
> + uffd_test_fail("moved destination is not a huge zeropage PMD");
> + } else if (!check_huge_anon(gopts->area_dst, 0, pmd_size)) {
> + /* vm_normal_page_pmd() must continue to treat the moved PMD as special. */
> + uffd_test_fail("moved huge zeropage PMD counted as AnonHugePages");
> + } else {
> + uffd_test_pass();
> + }
> +
> + gopts->area_src = orig_area_src;
> + gopts->area_dst = orig_area_dst;
> + close(pagemap_fd);
> +}
> +
> static void uffd_move_pmd_split_test(uffd_global_test_opts_t *gopts, uffd_test_args_t *targs)
> {
> if (madvise(gopts->area_dst, gopts->nr_pages * gopts->page_size, MADV_NOHUGEPAGE))
> @@ -1550,6 +1643,13 @@ uffd_test_case_t uffd_tests[] = {
> .uffd_feature_required = UFFD_FEATURE_MOVE,
> .test_case_ops = &uffd_move_test_pmd_case_ops,
> },
> + {
> + .name = "move-pmd-huge-zeropage",
> + .uffd_fn = uffd_move_pmd_huge_zeropage_test,
> + .mem_targets = MEM_ANON,
> + .uffd_feature_required = UFFD_FEATURE_MOVE,
> + .test_case_ops = &uffd_move_test_pmd_case_ops,
> + },
> {
> .name = "move-pmd-split",
> .uffd_fn = uffd_move_pmd_split_test,
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index a6d4ff7dfdc0..55cc4cc058a2 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -120,6 +120,18 @@ bool pagemap_is_populated(int fd, char *start)
> PAGE_IS_PRESENT | PAGE_IS_SWAPPED);
> }
>
> +bool pagemap_is_huge_zero(int fd, char *start)
> +{
> + uint64_t categories;
> +
> + if (!pagemap_scan_supported(fd, start))
> + return false;
> +
> + categories = pagemap_scan_get_categories(fd, start);
> + return (categories & (PAGE_IS_PRESENT | PAGE_IS_PFNZERO | PAGE_IS_HUGE)) ==
> + (PAGE_IS_PRESENT | PAGE_IS_PFNZERO | PAGE_IS_HUGE);
> +}
> +
> unsigned long pagemap_get_pfn(int fd, char *start)
> {
> uint64_t entry = pagemap_get_entry(fd, start);
> diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
> index e9c4e24769c1..e0b6ae1b12f5 100644
> --- a/tools/testing/selftests/mm/vm_util.h
> +++ b/tools/testing/selftests/mm/vm_util.h
> @@ -85,6 +85,7 @@ uint64_t pagemap_get_entry(int fd, char *start);
> bool pagemap_is_softdirty(int fd, char *start);
> bool pagemap_is_swapped(int fd, char *start);
> bool pagemap_is_populated(int fd, char *start);
> +bool pagemap_is_huge_zero(int fd, char *start);
> unsigned long pagemap_get_pfn(int fd, char *start);
> void clear_softdirty(void);
> bool check_for_pattern(FILE *fp, const char *pattern, char *buf, size_t len);
>
> base-commit: f0caa1d49cc07b30a7e2f104d3853ec6dc1c3cad
> --
> 2.53.0
>
--
Sincerely yours,
Mike.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v3] selftests/mm: Add UFFDIO_MOVE huge zeropage PMD regression test
2026-03-18 4:18 [PATCH v3] selftests/mm: Add UFFDIO_MOVE huge zeropage PMD regression test Chris Down
2026-03-19 15:42 ` Mike Rapoport
@ 2026-03-19 19:34 ` David Hildenbrand (Arm)
1 sibling, 0 replies; 3+ messages in thread
From: David Hildenbrand (Arm) @ 2026-03-19 19:34 UTC (permalink / raw)
To: Chris Down, Andrew Morton
Cc: Mike Rapoport, Peter Xu, Lorenzo Stoakes, Liam R. Howlett,
Vlastimil Babka, Suren Baghdasaryan, Michal Hocko, Shuah Khan,
Matthew Wilcox, kernel-team, linux-mm, linux-kselftest,
linux-kernel
On 3/18/26 05:18, Chris Down wrote:
> The existing uffd-unit-tests move-pmd coverage exercises PMD-sized
> UFFDIO_MOVE on anonymous THPs, but it does not force the huge zeropage
> PMD path in move_pages_huge_pmd().
>
> Add a dedicated anonymous UFFDIO_MOVE PMD test that exercises this
> relatively comprehensively.
>
> Signed-off-by: Chris Down <chris@chrisdown.name>
> ---
> tools/testing/selftests/mm/uffd-unit-tests.c | 100 +++++++++++++++++++
> tools/testing/selftests/mm/vm_util.c | 12 +++
> tools/testing/selftests/mm/vm_util.h | 1 +
> 3 files changed, 113 insertions(+)
>
> diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
> index 6f5e404a446c..9cc4cbab9a23 100644
> --- a/tools/testing/selftests/mm/uffd-unit-tests.c
> +++ b/tools/testing/selftests/mm/uffd-unit-tests.c
> @@ -1227,6 +1227,99 @@ static void uffd_move_pmd_test(uffd_global_test_opts_t *gopts, uffd_test_args_t
> uffd_move_pmd_handle_fault);
> }
>
> +static void uffd_move_pmd_huge_zeropage_test(uffd_global_test_opts_t *gopts,
> + uffd_test_args_t *targs)
> +{
> + unsigned long pmd_size = read_pmd_pagesize();
> + unsigned long pmd_pages;
> + unsigned long bytes = gopts->nr_pages * gopts->page_size;
> + char *orig_area_src = gopts->area_src, *orig_area_dst = gopts->area_dst;
> + char *aligned_src, *aligned_dst;
> + unsigned long src_offs, dst_offs, max_offs;
> + pthread_t uffd_mon;
> + struct uffd_args args = { 0 };
> + char c = '\0';
> + int pagemap_fd;
> +
> + if (pmd_size <= gopts->page_size) {
> + uffd_test_skip("huge page size is 0, feature missing?");
Wouldn't a check for 0 be
"!pmd_size" ? :)
But yes, this is unexpected. Maybe simply
"Could not detect PMD size"
> + return;
> + }
> + if (!detect_huge_zeropage()) {
> + uffd_test_skip("transparent huge zeropage disabled");
> + return;
> + }
> +
> + pmd_pages = pmd_size / gopts->page_size;
Might consider s/pmd_pages/nr_pages_per_pmd/
[...]
>
> +bool pagemap_is_huge_zero(int fd, char *start)
> +{
> + uint64_t categories;
> +
> + if (!pagemap_scan_supported(fd, start))
> + return false;
> +
> + categories = pagemap_scan_get_categories(fd, start);
A slightly nicer way to write it might be
const uint64_t expected = PAGE_IS_PRESENT | PAGE_IS_PFNZERO | PAGE_IS_HUGE;
...
return (categories & expected) == huge_zero;
In general, lgtm, thanks!
--
Cheers,
David
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-03-19 19:34 ` David Hildenbrand (Arm)
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