[PATCH v2 0/2] kselftest: mm: fix intermittent failure khugepaged test

[PATCH v2 0/2] kselftest: mm: fix intermittent failure khugepaged test

[Yeoreum Yun]

There are intermittent failures in collapse_max_ptes_swap() and
collapse_max_ptes_shared() when using the khugepaged_context:

  # Run test: collapse_max_ptes_shared (khugepaged:anon)
  # Allocate huge page... OK
  # Share huge page over fork()... OK
  # Trigger CoW on page 1023 of 2048... OK
  # Maybe collapse with max_ptes_shared exceeded.... OK
  # Trigger CoW on page 1024 of 2048... Fail
  Bail out! Unexpected huge page
  # Planned tests != run tests (26 != 23)
  # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0

  # Run test: collapse_max_ptes_swap (khugepaged:anon)
  # Swapout 257 of 2048 pages... OK
  # Maybe collapse with max_ptes_swap exceeded.... OK
  # Swapout 256 of 2048 pages... OK
  Bail out! Unexpected huge page
  # Planned tests != run tests (26 != 17)
  # Totals: pass:17 fail:0 xfail:0 xpass:0 skip:0 error:0

This happens because khugepaged may collapse the pages before wait_for_scan()
is called, causing a sanity check that expects uncollapsed pages to fail.

For example, in collapse_max_ptes_swap(), after faulting the pages back in
and paging out up to max_ptes_swap pages, khugepaged may collapse them again
before c->collapse() is called.

To prevent this, mark the VMA with MADV_NOHUGEPAGE after it has been
collapsed by wait_for_scan() for anon. This prevents khugepaged from
collapsing it again before c->collapse() is called.

Also, fix false-positive results when a child process fails in tests
such as collapse_fork*() or collapse_max_ptes_shared():

  # -------------------------
  # running ./khugepaged -s 2
  # -------------------------
  #
  # Run test: collapse_max_ptes_shared (khugepaged:anon)
  # Allocate huge page... OK
  # Share huge page over fork()... OK
  # Trigger CoW on page 1023 of 2048... OK
  # Maybe collapse with max_ptes_shared exceeded.... OK
  # Trigger CoW on page 1024 of 2048... Fail
  Bail out! Unexpected huge page
  # Planned tests != run tests (26 != 23)
  # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0  // child failed.
  # Check if parent still has huge page... OK              // parent hpage success
  ok 24 collapse_max_ptes_shared                           // considered as success
  ...
  # Totals: pass:26 fail:0 xfail:0 xpass:0 skip:0 error:0

This failure was observed on NVIDIA Spark with 16KB page and this patch
is based on mm/mm-unstable

---
Changes in v2:
- remove temporary enabled setup.
- Link to v1: https://lore.kernel.org/r/20260915-fix_khugepagd_fail-v1-0-bb6f04c8759f@arm.com

---
Yeoreum Yun (2):
      kselftest: mm: return fail when child test result is fail in khugepaged
      kselftest: mm: fix intermittent failure khugepaged test

 tools/testing/selftests/mm/khugepaged.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)
---
base-commit: 8d61431ed2607386b427752505379536eb634ce8
change-id: 20260915-fix_khugepagd_fail-9d8932689200

Best regards,
-- 
Sincerely,
Yeoreum Yun

[PATCH v2 1/2] kselftest: mm: return fail when child test result is fail in khugepaged

[Yeoreum Yun]

Although the child process in collapse_fork*() or collapse_max_ptes_shared()
reports `KSFT_FAIL`, the result is ignored because the test only checks
whether the parent’s page was collapsed into a huge page.

As a result, the test is considered successful whenever the parent’s page
is a huge page, even if the child test fails, as shown below:

  #
  # Run test: collapse_max_ptes_shared (khugepaged:anon)
  # Allocate huge page... OK
  # Share huge page over fork()... OK
  # Trigger CoW on page 1023 of 2048... OK
  # Maybe collapse with max_ptes_shared exceeded.... OK
  # Trigger CoW on page 1024 of 2048... Fail
  Bail out! Unexpected huge page
  # Planned tests != run tests (26 != 23)
  # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0  // child failed.
  # Check if parent still has huge page... OK              // parent hpage success
  ok 24 collapse_max_ptes_shared                           // considered as success
  ...
  # Totals: pass:26 fail:0 xfail:0 xpass:0 skip:0 error:0

To address this, propagate the child’s failure and skip the subsequent
check in the parent.

Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
 tools/testing/selftests/mm/khugepaged.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index f82673f5f6b47..c32244b565658 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1009,6 +1009,8 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
 
 	wait(&wstatus);
 	exit_status = WEXITSTATUS(wstatus);
+	if (exit_status == KSFT_FAIL)
+		goto out;
 
 	ksft_print_msg("Check if parent still has small page...");
 	if (ops->check_huge(p, hpage_pmd_size, 0, hpage_pmd_size))
@@ -1016,6 +1018,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
 	else
 		fail("Fail");
 	validate_memory(p, 0, page_size);
+out:
 	ops->cleanup_area(p, hpage_pmd_size);
 	ksft_test_result_report(exit_status, "%s\n", __func__);
 }
@@ -1056,6 +1059,8 @@ static void collapse_fork_compound(struct collapse_context *c, struct mem_ops *o
 
 	wait(&wstatus);
 	exit_status = WEXITSTATUS(wstatus);
+	if (exit_status == KSFT_FAIL)
+		goto out;
 
 	ksft_print_msg("Check if parent still has huge page...");
 	if (ops->check_huge(p, hpage_pmd_size, 1, hpage_pmd_size))
@@ -1063,6 +1068,7 @@ static void collapse_fork_compound(struct collapse_context *c, struct mem_ops *o
 	else
 		fail("Fail");
 	validate_memory(p, 0, hpage_pmd_size);
+out:
 	ops->cleanup_area(p, hpage_pmd_size);
 	ksft_test_result_report(exit_status, "%s\n", __func__);
 }
@@ -1114,6 +1120,8 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
 
 	wait(&wstatus);
 	exit_status = WEXITSTATUS(wstatus);
+	if (exit_status == KSFT_FAIL)
+		goto out;
 
 	ksft_print_msg("Check if parent still has huge page...");
 	if (ops->check_huge(p, hpage_pmd_size, 1, hpage_pmd_size))
@@ -1121,6 +1129,7 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
 	else
 		fail("Fail");
 	validate_memory(p, 0, hpage_pmd_size);
+out:
 	ops->cleanup_area(p, hpage_pmd_size);
 	ksft_test_result_report(exit_status, "%s\n", __func__);
 }

-- 
2.43.0

[PATCH v2 2/2] kselftest: mm: fix intermittent failure khugepaged test

[Yeoreum Yun]

There are intermittent failures in collapse_max_ptes_swap() and
collapse_max_ptes_shared() when using the khugepaged_context:

  // while running ./khugepaged -s 2

  # Run test: collapse_max_ptes_shared (khugepaged:anon)
  # Allocate huge page... OK
  # Share huge page over fork()... OK
  # Trigger CoW on page 1023 of 2048... OK
  # Maybe collapse with max_ptes_shared exceeded.... OK
  # Trigger CoW on page 1024 of 2048... Fail
  Bail out! Unexpected huge page
  # Planned tests != run tests (26 != 23)
  # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0

  # Run test: collapse_max_ptes_swap (khugepaged:anon)
  # Swapout 257 of 2048 pages... OK
  # Maybe collapse with max_ptes_swap exceeded.... OK
  # Swapout 256 of 2048 pages... OK
  Bail out! Unexpected huge page
  # Planned tests != run tests (26 != 17)
  # Totals: pass:17 fail:0 xfail:0 xpass:0 skip:0 error:0

This happens because khugepaged may collapse the pages before wait_for_scan()
is called, causing a sanity check that expects uncollapsed pages to fail.

For example, in collapse_max_ptes_swap(), after faulting the pages back in
and paging out up to max_ptes_swap pages, khugepaged may collapse them again
before c->collapse() is called.

To prevent this, mark the VMA with MADV_NOHUGEPAGE after it has been
collapsed by wait_for_scan() for anon. This prevents khugepaged from
collapsing it again before c->collapse() is called.

This failure was observed on NVIDIA Spark with 16KB page.

Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
 tools/testing/selftests/mm/khugepaged.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index c32244b565658..1aad4bb427ece 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -578,6 +578,9 @@ static bool wait_for_scan(const char *msg, char *p, size_t len,
 		usleep(TICK);
 	}
 
+	if (!strncmp(ops->name, "anon", 4))
+		madvise(p, len, MADV_NOHUGEPAGE);
+
 	return timeout == -1;
 }
 

-- 
2.43.0

Re: [PATCH v2 2/2] kselftest: mm: fix intermittent failure khugepaged test

[Baolin Wang]

On 9/21/26 6:35 PM, Yeoreum Yun wrote:
> There are intermittent failures in collapse_max_ptes_swap() and
> collapse_max_ptes_shared() when using the khugepaged_context:
> 
>    // while running ./khugepaged -s 2
> 
>    # Run test: collapse_max_ptes_shared (khugepaged:anon)
>    # Allocate huge page... OK
>    # Share huge page over fork()... OK
>    # Trigger CoW on page 1023 of 2048... OK
>    # Maybe collapse with max_ptes_shared exceeded.... OK
>    # Trigger CoW on page 1024 of 2048... Fail
>    Bail out! Unexpected huge page
>    # Planned tests != run tests (26 != 23)
>    # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
>    # Run test: collapse_max_ptes_swap (khugepaged:anon)
>    # Swapout 257 of 2048 pages... OK
>    # Maybe collapse with max_ptes_swap exceeded.... OK
>    # Swapout 256 of 2048 pages... OK
>    Bail out! Unexpected huge page
>    # Planned tests != run tests (26 != 17)
>    # Totals: pass:17 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
> This happens because khugepaged may collapse the pages before wait_for_scan()
> is called, causing a sanity check that expects uncollapsed pages to fail.
> 
> For example, in collapse_max_ptes_swap(), after faulting the pages back in
> and paging out up to max_ptes_swap pages, khugepaged may collapse them again
> before c->collapse() is called.
> 
> To prevent this, mark the VMA with MADV_NOHUGEPAGE after it has been
> collapsed by wait_for_scan() for anon. This prevents khugepaged from
> collapsing it again before c->collapse() is called.
> 
> This failure was observed on NVIDIA Spark with 16KB page.
> 
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>   tools/testing/selftests/mm/khugepaged.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
> index c32244b565658..1aad4bb427ece 100644
> --- a/tools/testing/selftests/mm/khugepaged.c
> +++ b/tools/testing/selftests/mm/khugepaged.c
> @@ -578,6 +578,9 @@ static bool wait_for_scan(const char *msg, char *p, size_t len,
>   		usleep(TICK);
>   	}
>   
> +	if (!strncmp(ops->name, "anon", 4))

We usually use the 'if (ops == &__anon_ops)' check in this file to 
identify anonymous test cases.

With that, LGTM.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>

> +		madvise(p, len, MADV_NOHUGEPAGE);
> +
>   	return timeout == -1;
>   }
>   
> 

Re: [PATCH v2 1/2] kselftest: mm: return fail when child test result is fail in khugepaged

[Baolin Wang]

On 9/21/26 6:35 PM, Yeoreum Yun wrote:
> Although the child process in collapse_fork*() or collapse_max_ptes_shared()
> reports `KSFT_FAIL`, the result is ignored because the test only checks
> whether the parent’s page was collapsed into a huge page.
> 
> As a result, the test is considered successful whenever the parent’s page
> is a huge page, even if the child test fails, as shown below:
> 
>    #
>    # Run test: collapse_max_ptes_shared (khugepaged:anon)
>    # Allocate huge page... OK
>    # Share huge page over fork()... OK
>    # Trigger CoW on page 1023 of 2048... OK
>    # Maybe collapse with max_ptes_shared exceeded.... OK
>    # Trigger CoW on page 1024 of 2048... Fail
>    Bail out! Unexpected huge page
>    # Planned tests != run tests (26 != 23)
>    # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0  // child failed.
>    # Check if parent still has huge page... OK              // parent hpage success
>    ok 24 collapse_max_ptes_shared                           // considered as success
>    ...
>    # Totals: pass:26 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
> To address this, propagate the child’s failure and skip the subsequent
> check in the parent.
> 
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---

Make sense to me.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

Re: [PATCH v2 2/2] kselftest: mm: fix intermittent failure khugepaged test

[Yeoreum Yun]

On Wed, Sep 23, 2026 at 11:28:33AM +0800, Baolin Wang wrote:
> 
> 
> On 9/21/26 6:35 PM, Yeoreum Yun wrote:
> > There are intermittent failures in collapse_max_ptes_swap() and
> > collapse_max_ptes_shared() when using the khugepaged_context:
> > 
> >    // while running ./khugepaged -s 2
> > 
> >    # Run test: collapse_max_ptes_shared (khugepaged:anon)
> >    # Allocate huge page... OK
> >    # Share huge page over fork()... OK
> >    # Trigger CoW on page 1023 of 2048... OK
> >    # Maybe collapse with max_ptes_shared exceeded.... OK
> >    # Trigger CoW on page 1024 of 2048... Fail
> >    Bail out! Unexpected huge page
> >    # Planned tests != run tests (26 != 23)
> >    # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0
> > 
> >    # Run test: collapse_max_ptes_swap (khugepaged:anon)
> >    # Swapout 257 of 2048 pages... OK
> >    # Maybe collapse with max_ptes_swap exceeded.... OK
> >    # Swapout 256 of 2048 pages... OK
> >    Bail out! Unexpected huge page
> >    # Planned tests != run tests (26 != 17)
> >    # Totals: pass:17 fail:0 xfail:0 xpass:0 skip:0 error:0
> > 
> > This happens because khugepaged may collapse the pages before wait_for_scan()
> > is called, causing a sanity check that expects uncollapsed pages to fail.
> > 
> > For example, in collapse_max_ptes_swap(), after faulting the pages back in
> > and paging out up to max_ptes_swap pages, khugepaged may collapse them again
> > before c->collapse() is called.
> > 
> > To prevent this, mark the VMA with MADV_NOHUGEPAGE after it has been
> > collapsed by wait_for_scan() for anon. This prevents khugepaged from
> > collapsing it again before c->collapse() is called.
> > 
> > This failure was observed on NVIDIA Spark with 16KB page.
> > 
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > ---
> >   tools/testing/selftests/mm/khugepaged.c | 3 +++
> >   1 file changed, 3 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
> > index c32244b565658..1aad4bb427ece 100644
> > --- a/tools/testing/selftests/mm/khugepaged.c
> > +++ b/tools/testing/selftests/mm/khugepaged.c
> > @@ -578,6 +578,9 @@ static bool wait_for_scan(const char *msg, char *p, size_t len,
> >   		usleep(TICK);
> >   	}
> > +	if (!strncmp(ops->name, "anon", 4))
> 
> We usually use the 'if (ops == &__anon_ops)' check in this file to identify
> anonymous test cases.

Yeap. That would be much clear.

> 
> With that, LGTM.
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>

Thanks!

-- 
Sincerely,
Yeoreum Yun

Re: [PATCH v2 2/2] kselftest: mm: fix intermittent failure khugepaged test

[Yeoreum Yun]

> 
> 
> On 9/21/26 6:35 PM, Yeoreum Yun wrote:
> > There are intermittent failures in collapse_max_ptes_swap() and
> > collapse_max_ptes_shared() when using the khugepaged_context:
> > 
> >    // while running ./khugepaged -s 2
> > 
> >    # Run test: collapse_max_ptes_shared (khugepaged:anon)
> >    # Allocate huge page... OK
> >    # Share huge page over fork()... OK
> >    # Trigger CoW on page 1023 of 2048... OK
> >    # Maybe collapse with max_ptes_shared exceeded.... OK
> >    # Trigger CoW on page 1024 of 2048... Fail
> >    Bail out! Unexpected huge page
> >    # Planned tests != run tests (26 != 23)
> >    # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0
> > 
> >    # Run test: collapse_max_ptes_swap (khugepaged:anon)
> >    # Swapout 257 of 2048 pages... OK
> >    # Maybe collapse with max_ptes_swap exceeded.... OK
> >    # Swapout 256 of 2048 pages... OK
> >    Bail out! Unexpected huge page
> >    # Planned tests != run tests (26 != 17)
> >    # Totals: pass:17 fail:0 xfail:0 xpass:0 skip:0 error:0
> > 
> > This happens because khugepaged may collapse the pages before wait_for_scan()
> > is called, causing a sanity check that expects uncollapsed pages to fail.
> > 
> > For example, in collapse_max_ptes_swap(), after faulting the pages back in
> > and paging out up to max_ptes_swap pages, khugepaged may collapse them again
> > before c->collapse() is called.
> > 
> > To prevent this, mark the VMA with MADV_NOHUGEPAGE after it has been
> > collapsed by wait_for_scan() for anon. This prevents khugepaged from
> > collapsing it again before c->collapse() is called.
> > 
> > This failure was observed on NVIDIA Spark with 16KB page.
> > 
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > ---
> >   tools/testing/selftests/mm/khugepaged.c | 3 +++
> >   1 file changed, 3 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
> > index c32244b565658..1aad4bb427ece 100644
> > --- a/tools/testing/selftests/mm/khugepaged.c
> > +++ b/tools/testing/selftests/mm/khugepaged.c
> > @@ -578,6 +578,9 @@ static bool wait_for_scan(const char *msg, char *p, size_t len,
> >   		usleep(TICK);
> >   	}
> > +	if (!strncmp(ops->name, "anon", 4))
> 
> We usually use the 'if (ops == &__anon_ops)' check in this file to identify
> anonymous test cases.
> 
> With that, LGTM.
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>

I think this is merged at mm/mm-unstable already So, I'll send
another patch to change it with is_anon().

Thanks!

-- 
Sincerely,
Yeoreum Yun

Re: [PATCH v2 2/2] kselftest: mm: fix intermittent failure khugepaged test

[David Hildenbrand (Arm)]

On 9/23/26 12:54, Yeoreum Yun wrote:
>>
>>
>> On 9/21/26 6:35 PM, Yeoreum Yun wrote:
>>> There are intermittent failures in collapse_max_ptes_swap() and
>>> collapse_max_ptes_shared() when using the khugepaged_context:
>>>
>>>    // while running ./khugepaged -s 2
>>>
>>>    # Run test: collapse_max_ptes_shared (khugepaged:anon)
>>>    # Allocate huge page... OK
>>>    # Share huge page over fork()... OK
>>>    # Trigger CoW on page 1023 of 2048... OK
>>>    # Maybe collapse with max_ptes_shared exceeded.... OK
>>>    # Trigger CoW on page 1024 of 2048... Fail
>>>    Bail out! Unexpected huge page
>>>    # Planned tests != run tests (26 != 23)
>>>    # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0
>>>
>>>    # Run test: collapse_max_ptes_swap (khugepaged:anon)
>>>    # Swapout 257 of 2048 pages... OK
>>>    # Maybe collapse with max_ptes_swap exceeded.... OK
>>>    # Swapout 256 of 2048 pages... OK
>>>    Bail out! Unexpected huge page
>>>    # Planned tests != run tests (26 != 17)
>>>    # Totals: pass:17 fail:0 xfail:0 xpass:0 skip:0 error:0
>>>
>>> This happens because khugepaged may collapse the pages before wait_for_scan()
>>> is called, causing a sanity check that expects uncollapsed pages to fail.
>>>
>>> For example, in collapse_max_ptes_swap(), after faulting the pages back in
>>> and paging out up to max_ptes_swap pages, khugepaged may collapse them again
>>> before c->collapse() is called.
>>>
>>> To prevent this, mark the VMA with MADV_NOHUGEPAGE after it has been
>>> collapsed by wait_for_scan() for anon. This prevents khugepaged from
>>> collapsing it again before c->collapse() is called.
>>>
>>> This failure was observed on NVIDIA Spark with 16KB page.
>>>
>>> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
>>> ---
>>>   tools/testing/selftests/mm/khugepaged.c | 3 +++
>>>   1 file changed, 3 insertions(+)
>>>
>>> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
>>> index c32244b565658..1aad4bb427ece 100644
>>> --- a/tools/testing/selftests/mm/khugepaged.c
>>> +++ b/tools/testing/selftests/mm/khugepaged.c
>>> @@ -578,6 +578,9 @@ static bool wait_for_scan(const char *msg, char *p, size_t len,
>>>   		usleep(TICK);
>>>   	}
>>> +	if (!strncmp(ops->name, "anon", 4))
>>
>> We usually use the 'if (ops == &__anon_ops)' check in this file to identify
>> anonymous test cases.
>>
>> With that, LGTM.
>> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> 
> I think this is merged at mm/mm-unstable already So, I'll send
> another patch to change it with is_anon().

Unless it is in mm-stable we can reasonably squash stuff or resend. This
shouldn't be an independent patch.

-- 
Cheers,

David

Re: [PATCH v2 2/2] kselftest: mm: fix intermittent failure khugepaged test

[Yeoreum Yun]

> On 9/23/26 12:54, Yeoreum Yun wrote:
> >>
> >>
> >> On 9/21/26 6:35 PM, Yeoreum Yun wrote:
> >>> There are intermittent failures in collapse_max_ptes_swap() and
> >>> collapse_max_ptes_shared() when using the khugepaged_context:
> >>>
> >>>    // while running ./khugepaged -s 2
> >>>
> >>>    # Run test: collapse_max_ptes_shared (khugepaged:anon)
> >>>    # Allocate huge page... OK
> >>>    # Share huge page over fork()... OK
> >>>    # Trigger CoW on page 1023 of 2048... OK
> >>>    # Maybe collapse with max_ptes_shared exceeded.... OK
> >>>    # Trigger CoW on page 1024 of 2048... Fail
> >>>    Bail out! Unexpected huge page
> >>>    # Planned tests != run tests (26 != 23)
> >>>    # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0
> >>>
> >>>    # Run test: collapse_max_ptes_swap (khugepaged:anon)
> >>>    # Swapout 257 of 2048 pages... OK
> >>>    # Maybe collapse with max_ptes_swap exceeded.... OK
> >>>    # Swapout 256 of 2048 pages... OK
> >>>    Bail out! Unexpected huge page
> >>>    # Planned tests != run tests (26 != 17)
> >>>    # Totals: pass:17 fail:0 xfail:0 xpass:0 skip:0 error:0
> >>>
> >>> This happens because khugepaged may collapse the pages before wait_for_scan()
> >>> is called, causing a sanity check that expects uncollapsed pages to fail.
> >>>
> >>> For example, in collapse_max_ptes_swap(), after faulting the pages back in
> >>> and paging out up to max_ptes_swap pages, khugepaged may collapse them again
> >>> before c->collapse() is called.
> >>>
> >>> To prevent this, mark the VMA with MADV_NOHUGEPAGE after it has been
> >>> collapsed by wait_for_scan() for anon. This prevents khugepaged from
> >>> collapsing it again before c->collapse() is called.
> >>>
> >>> This failure was observed on NVIDIA Spark with 16KB page.
> >>>
> >>> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> >>> ---
> >>>   tools/testing/selftests/mm/khugepaged.c | 3 +++
> >>>   1 file changed, 3 insertions(+)
> >>>
> >>> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
> >>> index c32244b565658..1aad4bb427ece 100644
> >>> --- a/tools/testing/selftests/mm/khugepaged.c
> >>> +++ b/tools/testing/selftests/mm/khugepaged.c
> >>> @@ -578,6 +578,9 @@ static bool wait_for_scan(const char *msg, char *p, size_t len,
> >>>   		usleep(TICK);
> >>>   	}
> >>> +	if (!strncmp(ops->name, "anon", 4))
> >>
> >> We usually use the 'if (ops == &__anon_ops)' check in this file to identify
> >> anonymous test cases.
> >>
> >> With that, LGTM.
> >> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> >> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> > 
> > I think this is merged at mm/mm-unstable already So, I'll send
> > another patch to change it with is_anon().
> 
> Unless it is in mm-stable we can reasonably squash stuff or resend. This
> shouldn't be an independent patch.

I see. Thanks!

-- 
Sincerely,
Yeoreum Yun