[PATCH] selftests/mm: skip split_huge_page_test without the split_huge_pages file

[PATCH] selftests/mm: skip split_huge_page_test without the split_huge_pages file

[Sasha Levin]

Every case in split_huge_page_test goes through
/sys/kernel/debug/split_huge_pages. When that file does not exist,
because debugfs is not mounted or the kernel has no CONFIG_DEBUG_FS, the
first write bails out of the whole test and it is reported as a failure:

  Bail out! write_file(/sys/kernel/debug/split_huge_pages): No such file or directory

Skip the test in that case.

Fixes: fa6c02315f74 ("mm: huge_memory: a new debugfs interface for splitting THP tests")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
Found with KernelCI's NVIDIA lab, which runs the tests in a chroot
without debugfs. Tested on an AMD EPYC 9655P with KernelCI's x86_64
build of next-20261104: without debugfs the test now skips, and with
debugfs mounted it still passes all 62 cases.

 tools/testing/selftests/mm/split_huge_page_test.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 33a2473327bb7..deabb7db06192 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -610,6 +610,9 @@ int main(int argc, char **argv)
 	if (!thp_is_enabled())
 		ksft_exit_skip("Transparent Hugepages not available\n");
 
+	if (access(SPLIT_DEBUGFS, W_OK))
+		ksft_exit_skip("%s: %s\n", SPLIT_DEBUGFS, strerror(errno));
+
 	if (argc > 1)
 		optional_xfs_path = argv[1];
 
-- 
2.53.0

Re: [PATCH] selftests/mm: skip split_huge_page_test without the split_huge_pages file

[Kiryl Shutsemau]

On Wed, Nov 04, 2026 at 10:02:42PM -0500, Sasha Levin wrote:
> Every case in split_huge_page_test goes through
> /sys/kernel/debug/split_huge_pages. When that file does not exist,
> because debugfs is not mounted or the kernel has no CONFIG_DEBUG_FS, the
> first write bails out of the whole test and it is reported as a failure:
> 
>   Bail out! write_file(/sys/kernel/debug/split_huge_pages): No such file or directory
> 
> Skip the test in that case.
> 
> Fixes: fa6c02315f74 ("mm: huge_memory: a new debugfs interface for splitting THP tests")
> Signed-off-by: Sasha Levin <sashal@kernel.org>

Acked-by: Kiryl Shutsemau (Meta) <kas@kernel.org>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCH] selftests/mm: skip split_huge_page_test without the split_huge_pages file

[Zi Yan]

On 4 Nov 2026, at 22:02, Sasha Levin wrote:

> Every case in split_huge_page_test goes through
> /sys/kernel/debug/split_huge_pages. When that file does not exist,
> because debugfs is not mounted or the kernel has no CONFIG_DEBUG_FS, the
> first write bails out of the whole test and it is reported as a failure:
>
>   Bail out! write_file(/sys/kernel/debug/split_huge_pages): No such file or directory
>
> Skip the test in that case.
>
> Fixes: fa6c02315f74 ("mm: huge_memory: a new debugfs interface for splitting THP tests")
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> Found with KernelCI's NVIDIA lab, which runs the tests in a chroot
> without debugfs. Tested on an AMD EPYC 9655P with KernelCI's x86_64
> build of next-20261104: without debugfs the test now skips, and with
> debugfs mounted it still passes all 62 cases.
>
>  tools/testing/selftests/mm/split_huge_page_test.c | 3 +++
>  1 file changed, 3 insertions(+)
>

Thanks. But I do think we need a way of specifying the necessary
Kconfig options for selftests. Oh, we do have one:
https://elixir.bootlin.com/linux/v7.3.1/source/tools/testing/selftests/mm/config. Can you add CONFIG_DEBUG_FS=y to it while at it?

Otherwise, LGTM.

Acked-by: Zi Yan <ziy@nvidia.com>

Best Regards,
Yan, Zi

Re: [PATCH] selftests/mm: skip split_huge_page_test without the split_huge_pages file

[David Hildenbrand (Arm)]

On 11/5/26 16:19, Zi Yan wrote:
> On 4 Nov 2026, at 22:02, Sasha Levin wrote:
> 
>> Every case in split_huge_page_test goes through
>> /sys/kernel/debug/split_huge_pages. When that file does not exist,
>> because debugfs is not mounted or the kernel has no CONFIG_DEBUG_FS, the
>> first write bails out of the whole test and it is reported as a failure:
>>
>>   Bail out! write_file(/sys/kernel/debug/split_huge_pages): No such file or directory
>>
>> Skip the test in that case.
>>
>> Fixes: fa6c02315f74 ("mm: huge_memory: a new debugfs interface for splitting THP tests")
>> Signed-off-by: Sasha Levin <sashal@kernel.org>
>> ---
>> Found with KernelCI's NVIDIA lab, which runs the tests in a chroot
>> without debugfs. Tested on an AMD EPYC 9655P with KernelCI's x86_64
>> build of next-20261104: without debugfs the test now skips, and with
>> debugfs mounted it still passes all 62 cases.
>>
>>  tools/testing/selftests/mm/split_huge_page_test.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
> 
> Thanks. But I do think we need a way of specifying the necessary
> Kconfig options for selftests. Oh, we do have one:
> https://elixir.bootlin.com/linux/v7.3.1/source/tools/testing/selftests/mm/config. Can you add CONFIG_DEBUG_FS=y to it while at it?

Just what I was thinking.

-- 
Cheers,

David

[PATCH] selftests/mm: add CONFIG_DEBUG_FS to the config fragment

[Sasha Levin]

The split_huge_page and gup tests need debugfs, and CONFIG_GUP_TEST
depends on it. Add CONFIG_DEBUG_FS=y to the fragment.

Suggested-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
Merged into an x86_64 tinyconfig, the fragment leaves CONFIG_DEBUG_FS
and CONFIG_GUP_TEST unset without this change and sets both with it.
x86_64_defconfig already has CONFIG_DEBUG_FS=y and is unaffected.

 tools/testing/selftests/mm/config | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/mm/config b/tools/testing/selftests/mm/config
index 06f78bd232e2e..ff85b358d04cc 100644
--- a/tools/testing/selftests/mm/config
+++ b/tools/testing/selftests/mm/config
@@ -4,6 +4,7 @@ CONFIG_PTE_MARKER_UFFD_WP=y
 CONFIG_TEST_VMALLOC=m
 CONFIG_DEVICE_PRIVATE=y
 CONFIG_TEST_HMM=m
+CONFIG_DEBUG_FS=y
 CONFIG_GUP_TEST=y
 CONFIG_TRANSPARENT_HUGEPAGE=y
 CONFIG_MEM_SOFT_DIRTY=y

base-commit: dba8aba0a9a00ff781c03d82ae534fc6f8c2e263
-- 
2.53.0

Re: [PATCH] selftests/mm: add CONFIG_DEBUG_FS to the config fragment

[Zi Yan]

On 5 Nov 2026, at 12:18, Sasha Levin wrote:

> The split_huge_page and gup tests need debugfs, and CONFIG_GUP_TEST
> depends on it. Add CONFIG_DEBUG_FS=y to the fragment.
>
> Suggested-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> Merged into an x86_64 tinyconfig, the fragment leaves CONFIG_DEBUG_FS
> and CONFIG_GUP_TEST unset without this change and sets both with it.
> x86_64_defconfig already has CONFIG_DEBUG_FS=y and is unaffected.
>

Thanks.

Reviewed-by: Zi Yan <ziy@nvidia.com>

Best Regards,
Yan, Zi

Re: [PATCH] selftests/mm: add CONFIG_DEBUG_FS to the config fragment

[David Hildenbrand (Arm)]

On 11/5/26 18:21, Zi Yan wrote:
> On 5 Nov 2026, at 12:18, Sasha Levin wrote:
> 
>> The split_huge_page and gup tests need debugfs, and CONFIG_GUP_TEST
>> depends on it. Add CONFIG_DEBUG_FS=y to the fragment.
>>
>> Suggested-by: Zi Yan <ziy@nvidia.com>
>> Signed-off-by: Sasha Levin <sashal@kernel.org>
>> ---
>> Merged into an x86_64 tinyconfig, the fragment leaves CONFIG_DEBUG_FS
>> and CONFIG_GUP_TEST unset without this change and sets both with it.
>> x86_64_defconfig already has CONFIG_DEBUG_FS=y and is unaffected.
>>
> 
> Thanks.
> 
> Reviewed-by: Zi Yan <ziy@nvidia.com>

Thanks, I'll wait a bit and then queue both.

-- 
Cheers,

David

Re: [PATCH] selftests/mm: add CONFIG_DEBUG_FS to the config fragment

[David Hildenbrand]

On Thu, 05 Nov 2026 12:18:01 -0500, Sasha Levin wrote:
> The split_huge_page and gup tests need debugfs, and CONFIG_GUP_TEST
> depends on it. Add CONFIG_DEBUG_FS=y to the fragment.

Applied, thanks!

tree: mm/core.git
branch: thp-7.5.misc

Applied patches will appear soon in mm-next, followed by linux-next.

Please report any outstanding bugs that were missed during review, so we
can either drop the patch series or decide how to fix it up.

It is encouraged to provide Acked-bys, Reviewed-bys, and Tested-bys even
though the patches have already been applied. If possible, patch trailers
will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. Further, this is not a guarantee that the
patches will go upstream. If in doubt, please check the listed branch.

[1/1] selftests/mm: add CONFIG_DEBUG_FS to the config fragment
      https://git.kernel.org/mm/core/c/31ea5515

-- 
Cheers,

David

Re: [PATCH] selftests/mm: add CONFIG_DEBUG_FS to the config fragment

[David Hildenbrand]

On Thu, 05 Nov 2026 12:18:01 -0500, Sasha Levin wrote:
> The split_huge_page and gup tests need debugfs, and CONFIG_GUP_TEST
> depends on it. Add CONFIG_DEBUG_FS=y to the fragment.

Applied, thanks!

tree: mm/core.git
branch: core-7.5.misc

Applied patches will appear soon in mm-next, followed by linux-next.

Please report any outstanding bugs that were missed during review, so we
can either drop the patch series or decide how to fix it up.

It is encouraged to provide Acked-bys, Reviewed-bys, and Tested-bys even
though the patches have already been applied. If possible, patch trailers
will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. Further, this is not a guarantee that the
patches will go upstream. If in doubt, please check the listed branch.

[1/1] selftests/mm: add CONFIG_DEBUG_FS to the config fragment
      https://git.kernel.org/mm/core/c/194b6319

-- 
Cheers,

David

Re: [PATCH] selftests/mm: add CONFIG_DEBUG_FS to the config fragment

[Sasha Levin]

On Fri, 06 Nov 2026 15:17:55 +0100, David Hildenbrand wrote:
>[1/1] selftests/mm: add CONFIG_DEBUG_FS to the config fragment
>      https://git.kernel.org/mm/core/c/31ea5515

Thanks! It looks like this one landed on both thp-7.5.misc and
core-7.5.misc:

  31ea5515bf59 ("selftests/mm: add CONFIG_DEBUG_FS to the config fragment")
  194b63198811 ("selftests/mm: add CONFIG_DEBUG_FS to the config fragment")

Was the thp-7.5.misc one meant to be the split_huge_page_test skip patch?

  https://lore.kernel.org/all/20261105030242.1241448-1-sashal@kernel.org/

--
Thanks,
Sasha

Re: [PATCH] selftests/mm: add CONFIG_DEBUG_FS to the config fragment

[David Hildenbrand (Arm)]

On 11/6/26 19:52, Sasha Levin wrote:
> On Fri, 06 Nov 2026 15:17:55 +0100, David Hildenbrand wrote:
>> [1/1] selftests/mm: add CONFIG_DEBUG_FS to the config fragment
>>      https://git.kernel.org/mm/core/c/31ea5515
> 
> Thanks! It looks like this one landed on both thp-7.5.misc and
> core-7.5.misc:
> 
>   31ea5515bf59 ("selftests/mm: add CONFIG_DEBUG_FS to the config fragment")
>   194b63198811 ("selftests/mm: add CONFIG_DEBUG_FS to the config fragment")
> 
> Was the thp-7.5.misc one meant to be the split_huge_page_test skip patch?
> 
>   https://lore.kernel.org/all/20261105030242.1241448-1-sashal@kernel.org/

Fixes.

b4 shazam gets confused when patches are sent in reply to patches.

Which is why we shouldn't do it ;)

-- 
Cheers,

David

Re: [PATCH] selftests/mm: add CONFIG_DEBUG_FS to the config fragment

[Sasha Levin]

On Fri, Nov 06, 2026 at 10:32:27PM +0100, David Hildenbrand (Arm) wrote:
>On 11/6/26 19:52, Sasha Levin wrote:
>> On Fri, 06 Nov 2026 15:17:55 +0100, David Hildenbrand wrote:
>>> [1/1] selftests/mm: add CONFIG_DEBUG_FS to the config fragment
>>>      https://git.kernel.org/mm/core/c/31ea5515
>>
>> Thanks! It looks like this one landed on both thp-7.5.misc and
>> core-7.5.misc:
>>
>>   31ea5515bf59 ("selftests/mm: add CONFIG_DEBUG_FS to the config fragment")
>>   194b63198811 ("selftests/mm: add CONFIG_DEBUG_FS to the config fragment")
>>
>> Was the thp-7.5.misc one meant to be the split_huge_page_test skip patch?
>>
>>   https://lore.kernel.org/all/20261105030242.1241448-1-sashal@kernel.org/
>
>Fixes.
>
>b4 shazam gets confused when patches are sent in reply to patches.
>
>Which is why we shouldn't do it ;)

Remember my gripe about how subsystems are starting to have more and more
custom rules around process? :p

Our docs currently say (Documentation/process/submitting-patches.rst):

	Explicit In-Reply-To headers
	----------------------------

	It can be helpful to manually add In-Reply-To: headers to a patch
	(e.g., when using ``git send-email``) to associate the patch with
	previous relevant discussion, e.g. to link a bug fix to the email with
	the bug report.

I suppose it's okay for parts of the kernel to deviate from the "standard", but
it's a bit hard to keep track of these preferences.

-- 
Thanks,
Sasha

Re: [PATCH] selftests/mm: add CONFIG_DEBUG_FS to the config fragment

[David Hildenbrand (Arm)]

On 11/7/26 13:42, Sasha Levin wrote:
> On Fri, Nov 06, 2026 at 10:32:27PM +0100, David Hildenbrand (Arm) wrote:
>> On 11/6/26 19:52, Sasha Levin wrote:
>>>
>>> Thanks! It looks like this one landed on both thp-7.5.misc and
>>> core-7.5.misc:
>>>
>>>   31ea5515bf59 ("selftests/mm: add CONFIG_DEBUG_FS to the config fragment")
>>>   194b63198811 ("selftests/mm: add CONFIG_DEBUG_FS to the config fragment")
>>>
>>> Was the thp-7.5.misc one meant to be the split_huge_page_test skip patch?
>>>
>>>   https://lore.kernel.org/all/20261105030242.1241448-1-sashal@kernel.org/
>>
>> Fixes.
>>
>> b4 shazam gets confused when patches are sent in reply to patches.
>>
>> Which is why we shouldn't do it ;)
> 
> Remember my gripe about how subsystems are starting to have more and more
> custom rules around process? :p

Let's not twist my words. I said "we shouldn't do it", there are no rules around
it and also I don't want any rules around that.

And the example below (bug vs. bug report) makes perfect sense.

> 
> Our docs currently say (Documentation/process/submitting-patches.rst):
> 
> 	Explicit In-Reply-To headers
> 	----------------------------
> 
> 	It can be helpful to manually add In-Reply-To: headers to a patch
> 	(e.g., when using ``git send-email``) to associate the patch with
> 	previous relevant discussion, e.g. to link a bug fix to the email with
> 	the bug report.
> 
> I suppose it's okay for parts of the kernel to deviate from the "standard", but
> it's a bit hard to keep track of these preferences.

Just to be clear, patch in reply to patch to me is something different than
patch in reply to discussion.

People tend to ignore certain patches because it's not relevant for them;
burying something related but more generic in there is not always the best idea.

But it all doesn't matter, because there are not any such strict rules and I
just have to learn to properly use b4 :P

-- 
Cheers,

David

Re: [PATCH] selftests/mm: skip split_huge_page_test without the split_huge_pages file

[Baolin Wang]

On 11/5/26 11:02 AM, Sasha Levin wrote:
> Every case in split_huge_page_test goes through
> /sys/kernel/debug/split_huge_pages. When that file does not exist,
> because debugfs is not mounted or the kernel has no CONFIG_DEBUG_FS, the
> first write bails out of the whole test and it is reported as a failure:
> 
>    Bail out! write_file(/sys/kernel/debug/split_huge_pages): No such file or directory
> 
> Skip the test in that case.
> 
> Fixes: fa6c02315f74 ("mm: huge_memory: a new debugfs interface for splitting THP tests")
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---

Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>