linux-kernel - Re: [PATCH 1/2] selftests/mm: fix hugepages cleanup too early

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Message-ID: <87956f34-e6b0-4d03-b30e-56be4f6b84f1@redhat.com>
Date: Wed, 27 Aug 2025 13:41:34 +0200
From: David Hildenbrand <david@...hat.com>
To: Chunyu Hu <chuhu@...hat.com>, akpm@...ux-foundation.org,
 shuah@...nel.org, linux-mm@...ck.org
Cc: linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
 lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, vbabka@...e.cz,
 rppt@...nel.org, surenb@...gle.com, mhocko@...e.com
Subject: Re: [PATCH 1/2] selftests/mm: fix hugepages cleanup too early

On 27.08.25 09:52, Chunyu Hu wrote:
> The nr_hugepgs variable is used to keep the original nr_hugepages at the
> hugepage setup step at test beginning. After userfaultfd test, a cleaup is
> executed, both /sys/kernel/mm/hugepages/hugepages-*/nr_hugepages and
> /proc/sys//vm/nr_hugepages are reset to 'original' value before userfaultfd
> test starts.
> 
> Issue here is the value used to restore /proc/sys/vm/nr_hugepages is
> nr_hugepgs which is the initial value before the vm_runtests.sh runs, not
> the value before userfaultfd test starts. 'va_high_addr_swith.sh' tests
> runs after that will possibly see no hugepages available for test, and got
> EINVAL when mmap(HUGETLB), making the result invalid.
> 
> And before pkey tests, nr_hugepgs is changed to be used as a temp variable
> to save nr_hugepages before pkey test, and restore it after pkey tests
> finish. The original nr_hugepages value is not tracked anymore, so no way
> to restore it after all tests finish.
> 
> Add a new variable nr_hugepgs_origin to save the original nr_hugepages, and
> and restore it to nr_hugepages after all tests finish. And change to use
> the nr_hugepgs variable to save the /proc/sys/vm/nr_hugeages after hugepage
> setup, it's also the value before userfaultfd test starts, and the correct
> value to be restored after userfaultfd finishes. The va_high_addr_switch.sh
> broken will be resolved.
> 
> Signed-off-by: Chunyu Hu <chuhu@...hat.com>
> ---
>   tools/testing/selftests/mm/run_vmtests.sh | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
> index 471e539d82b8..f1a7ad3ec6a7 100755
> --- a/tools/testing/selftests/mm/run_vmtests.sh
> +++ b/tools/testing/selftests/mm/run_vmtests.sh
> @@ -172,13 +172,13 @@ fi
>   
>   # set proper nr_hugepages
>   if [ -n "$freepgs" ] && [ -n "$hpgsize_KB" ]; then
> -	nr_hugepgs=$(cat /proc/sys/vm/nr_hugepages)
> +	nr_hugepgs_origin=$(cat /proc/sys/vm/nr_hugepages)

I'd call this "orig_nr_hugepgs".

But it's a shame that the naming is then out of sync with nr_size_hugepgs?


>   	needpgs=$((needmem_KB / hpgsize_KB))
>   	tries=2
>   	while [ "$tries" -gt 0 ] && [ "$freepgs" -lt "$needpgs" ]; do
>   		lackpgs=$((needpgs - freepgs))
>   		echo 3 > /proc/sys/vm/drop_caches
> -		if ! echo $((lackpgs + nr_hugepgs)) > /proc/sys/vm/nr_hugepages; then
> +		if ! echo $((lackpgs + nr_hugepgs_origin)) > /proc/sys/vm/nr_hugepages; then
>   			echo "Please run this test as root"
>   			exit $ksft_skip
>   		fi
> @@ -189,6 +189,7 @@ if [ -n "$freepgs" ] && [ -n "$hpgsize_KB" ]; then
>   		done < /proc/meminfo
>   		tries=$((tries - 1))
>   	done
> +	nr_hugepgs=$(cat /proc/sys/vm/nr_hugepages)
>   	if [ "$freepgs" -lt "$needpgs" ]; then
>   		printf "Not enough huge pages available (%d < %d)\n" \
>   		       "$freepgs" "$needpgs"
> @@ -532,6 +533,10 @@ CATEGORY="page_frag" run_test ./test_page_frag.sh aligned
>   
>   CATEGORY="page_frag" run_test ./test_page_frag.sh nonaligned
>   
> +if [ "${HAVE_HUGEPAGES}" = 1 ]; then
> +	echo "$nr_hugepgs_origin" > /proc/sys/vm/nr_hugepages
> +fi

FWIW, I think the tests should maybe be doing that 
(save+configure+restore) themselves, like we do with THP settings through.

thp_save_settings()
thp_write_settings()

and friends.

This is not really something run_vmtests.sh should bother with.

A bigger rework, though ...

-- 
Cheers

David / dhildenb