Hello.
Running the mm selftests from the kernel's root directory on an x86_64 debian machine using:
make defconfig sudo make kselftest TARGETS=mm
the tests run normally till we reach one which stalls for 180 seconds and times out according to the following logs:
``` ----------------------------------------------- running ./charge_reserved_hugetlb.sh -cgroup-v2 ----------------------------------------------- CLEANUP DONE CLEANUP DONE Test normal case. private=, populate=, method=0, reserve= nr hugepages = 10 writing cgroup limit: 20971520 writing reseravation limit: 20971520
Starting: hugetlb_usage=0 reserved_usage=0 expect_failure is 0 Putting task in cgroup 'hugetlb_cgroup_test' Method is 0
write_hugetlb_memory.sh: line 22: ./write_to_hugetlbfs: No such file or directory <<<
Waiting for hugetlb memory reservation to reach size 10485760. 0 Waiting for hugetlb memory reservation to reach size 10485760. 0 ... Waiting for hugetlb memory reservation to reach size 10485760. 0 Waiting for hugetlb memory reservation to reach size 10485760. 0
not ok 1 selftests: mm: run_vmtests.sh # TIMEOUT 180 seconds make[3]: Leaving directory '/linux/tools/testing/selftests/mm' ```
Logs show that the executable "write_to_hugetlbfs" is missing, causing the test to hang waiting for hugepage reservations.
The executable not found means it was not built by the Make system. It is mentioned in Makefile:136-142, and only built if ARCH is 64-bit
``` ifneq (,$(filter $(ARCH),arm64 mips64 parisc64 powerpc riscv64 s390x sparc64 x86_64 s390)) TEST_GEN_FILES += va_high_addr_switch ifneq ($(ARCH),riscv64) TEST_GEN_FILES += virtual_address_range endif TEST_GEN_FILES += write_to_hugetlbfs endif ```
So, for some reason, the top-level Makefile provides ARCH as x86.
My proposed solution is similar to existing virtual_address_range check that is to check for the binary, and if it is not found, skip these 2 test cases: charge_reserved_hugetlb.sh and hugetlb_reparenting_test.sh since they directly and indirectly depend on write_to_hugetlbfs binary.
This is just a workaround, the root issue of different ARCH detection when running tests from the kernel root directory should still be addressed. I am not sure how to approach it and open for your suggestions.
Note that this issue does not happen when ran from selftests/mm using something like
sudo make -C tools/testing/selftests/mm
because then mm/Makefile's ARCH detection runs correctly (x86_64)
Kindly review and share your thoughts.
Signed-off-by: Khaled Elnaggar khaledelnaggarlinux@gmail.com --- tools/testing/selftests/mm/run_vmtests.sh | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh index dddd1dd8af14..cdbcfdb62f8a 100755 --- a/tools/testing/selftests/mm/run_vmtests.sh +++ b/tools/testing/selftests/mm/run_vmtests.sh @@ -375,8 +375,13 @@ CATEGORY="process_mrelease" run_test ./mrelease_test CATEGORY="mremap" run_test ./mremap_test
CATEGORY="hugetlb" run_test ./thuge-gen + +# the following depend on write_to_hugetlbfs binary +if [ -x ./write_to_hugetlbfs ]; then CATEGORY="hugetlb" run_test ./charge_reserved_hugetlb.sh -cgroup-v2 CATEGORY="hugetlb" run_test ./hugetlb_reparenting_test.sh -cgroup-v2 +fi + if $RUN_DESTRUCTIVE; then nr_hugepages_tmp=$(cat /proc/sys/vm/nr_hugepages) enable_soft_offline=$(cat /proc/sys/vm/enable_soft_offline) -- 2.47.2
On 5/23/25 12:43, Khaled Elnaggar wrote:
Hello.
The above doesn't belong in change log. Refer to a few change logs in the repo to learn how to write them.
You can also check the kernel documentation - this change log is way too long. It doesn't clearly state what is being fixed.
In this case, "write_to_hugetlbfs" is missing because the right config isn't enabled. Test stalls waiting for write_to_hugetlbfs to run.
You are fixing this by checking if write_to_hugetlbfs exixts from /mm/run_vmtests.sh
Summarize this in short description so people can understand the change.
thanks, -- Shuah
On 24/05/2025 12:09 am, Shuah Khan wrote:
On 5/23/25 12:43, Khaled Elnaggar wrote:
Hello.
The above doesn't belong in change log. Refer to a few change logs in the repo to learn how to write them.
You can also check the kernel documentation - this change log is way too long. It doesn't clearly state what is being fixed.
In this case, "write_to_hugetlbfs" is missing because the right config isn't enabled. Test stalls waiting for write_to_hugetlbfs to run.
You are fixing this by checking if write_to_hugetlbfs exixts from /mm/run_vmtests.sh
Summarize this in short description so people can understand the change.
thanks, -- Shuah
Oh, I mistakenly thought since RFC does not get merged into source tree, it could have a relaxed tone, hence the much text.
Appreciate your feedback, I will rewrite the patch considering the points mentioned. Thank you.
The hugevm tests 'charge_reserved_hugetlb.sh' and 'hugetlb_reparenting_test.sh' depend on the 'write_to_hugetlbfs' binary to simulate writes to hugetlbfs while checking reservations asynchronously in the background.
When this binary is missing (e.g., excluded from the build), these tests hang for up to 180 seconds. During this time, run_vmtests.sh is eventually killed due to timeout, aborting all subsequent tests.
This patch skips these tests if the binary is not found, preventing delays and ensuring that the test suite runs to completion.
Signed-off-by: Khaled Elnaggar khaledelnaggarlinux@gmail.com --- tools/testing/selftests/mm/run_vmtests.sh | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh index dddd1dd8af14..0b55395ee2cb 100755 --- a/tools/testing/selftests/mm/run_vmtests.sh +++ b/tools/testing/selftests/mm/run_vmtests.sh @@ -375,8 +375,13 @@ CATEGORY="process_mrelease" run_test ./mrelease_test CATEGORY="mremap" run_test ./mremap_test
CATEGORY="hugetlb" run_test ./thuge-gen + +# the following tests depend on write_to_hugetlbfs binary +if [ -x ./write_to_hugetlbfs ]; then CATEGORY="hugetlb" run_test ./charge_reserved_hugetlb.sh -cgroup-v2 CATEGORY="hugetlb" run_test ./hugetlb_reparenting_test.sh -cgroup-v2 +fi + if $RUN_DESTRUCTIVE; then nr_hugepages_tmp=$(cat /proc/sys/vm/nr_hugepages) enable_soft_offline=$(cat /proc/sys/vm/enable_soft_offline) -- 2.47.2
On Tue, 3 Jun 2025 02:22:32 +0300 Khaled Elnaggar khaledelnaggarlinux@gmail.com wrote:
The hugevm tests 'charge_reserved_hugetlb.sh' and 'hugetlb_reparenting_test.sh' depend on the 'write_to_hugetlbfs' binary to simulate writes to hugetlbfs while checking reservations asynchronously in the background.
When this binary is missing (e.g., excluded from the build), these tests hang for up to 180 seconds. During this time, run_vmtests.sh is eventually killed due to timeout, aborting all subsequent tests.
This patch skips these tests if the binary is not found, preventing delays and ensuring that the test suite runs to completion.
OK, but why is write_to_hugetlbfs missing? If we're in a situation where we _could_ run it then we _should_ run it! The user wants to test stuff so we should test as much as we can.
So I'm thinking that it would be preferable to make sure the dang thing is there?
On 03/06/2025 5:12 am, Andrew Morton wrote:
On Tue, 3 Jun 2025 02:22:32 +0300 Khaled Elnaggar khaledelnaggarlinux@gmail.com wrote:
The hugevm tests 'charge_reserved_hugetlb.sh' and 'hugetlb_reparenting_test.sh' depend on the 'write_to_hugetlbfs' binary to simulate writes to hugetlbfs while checking reservations asynchronously in the background.
When this binary is missing (e.g., excluded from the build), these tests hang for up to 180 seconds. During this time, run_vmtests.sh is eventually killed due to timeout, aborting all subsequent tests.
This patch skips these tests if the binary is not found, preventing delays and ensuring that the test suite runs to completion.
OK, but why is write_to_hugetlbfs missing? If we're in a situation where we _could_ run it then we _should_ run it! The user wants to test stuff so we should test as much as we can. So I'm thinking that it would be preferable to make sure the dang thing is there?
Totally agree, let me try to explain how I understand the issue.
The write_to_hugetlbfs binary is built from selftests/mm/Makefile, lines 136–142. It is only compiled if ARCH matches one of the explicitly listed 64-bit architectures:
``` ifneq (,$(filter $(ARCH),arm64 mips64 parisc64 powerpc riscv64 s390x sparc64 x86_64 s390)) TEST_GEN_FILES += va_high_addr_switch ifneq ($(ARCH),riscv64) TEST_GEN_FILES += virtual_address_range endif TEST_GEN_FILES += write_to_hugetlbfs endif ```
However, when the MM selftests are run from the kernel’s top-level Makefile, (root directory for example:
make defconfig sudo make kselftest TARGETS=mm
ARCH is resolved as x86, even on an x86_64 machine (Debian in my case), ARCH=x86 is the reason why the binary gets excluded from the build system.
As far as I understand, the top-level Makefile normalizes both i.86 and x86_64 to x86 for ARCH variable:
Makfile: lines: 383,403 383:include $(srctree)/scripts/subarch.include 403:ARCH ?= $(SUBARCH)
scripts/subarch.include: line: 7 7:SUBARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
This mapping probably makes sense for selecting the correct arch/ directory (since we have arch/x86, not arch/x86_64) for top-level Makefile.
But the mm selftests Makefile expects ARCH to differentiate between x86 and x86_64 to decide whether to build certain binaries. As a result, the 64-bit-only binaries like write_to_hugetlbfs are skipped during build, yet still expected at runtime (by run_vmtests.sh).
That's why this whole issue of the missing executable does not happen when ran from selftests/mm using something like:
sudo make -C tools/testing/selftests/mm
Because then selftests/mm/Makefile arch detection rus as intended.
You're right — the proper fix is to improve how we propagate architecture information from the top-level Makefile to selftests. But since that's a larger change (and possibly beyond what I can safely attempt at this point), this patch is just a targeted workaround to avoid test stalls when the binary is missing.
I hope I haven't gone completely wrong with this analysis, happy to improve or revise it further if needed.
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Andrew Morton -
Khaled Elnaggar -
Shuah Khan