Re: [PATCH v2 1/3] selftests/mm: handle EINVAL when configuring gigantic hugepages

["David Hildenbrand (Arm)" <david@kernel.org>]

On 6/30/26 11:32, Sayali Patil wrote:
> Some MM selftests attempt to configure the amount of
> HugeTLB pages of different sizes by writing to nr_hugepages.
> 
> PowerPC hash MMU pSeries systems advertise gigantic hugepage sizes
> but do not support runtime allocation of such pages, writes
> to the corresponding nr_hugepages file fail with -EINVAL.
> This causes the test to bail out even though the failure is due
> to a platform limitation rather than the
> functionality being tested.
> 
> Treat -EINVAL from the sysfs write as a skipped configuration request
> and continue running the test instead of failing.
> 
> Before patch:
>    -------------------------
>    running ./hugetlb-madvise
>    -------------------------
>    TAP version 13
>    1..1
>      [INFO] detected hugetlb page size: 16777216 KiB
>      [INFO] detected hugetlb page size: 16384 KiB
>     ok 1 MADV_DONTNEED and MADV_REMOVE on hugetlb
>     Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
>     Bail out! /sys/kernel/mm/hugepages/hugepages-16777216kB/nr_hugepages
>     write(0) failed: Invalid argument
>     Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0
>     [FAIL]
> 
> After patch:
>    -------------------------
>    running ./hugetlb-madvise
>    -------------------------
>    TAP version 13
>    1..1
>     [INFO] detected hugetlb page size: 16777216 KiB
>     [INFO] detected hugetlb page size: 16384 KiB
>    ok 1 MADV_DONTNEED and MADV_REMOVE on hugetlb
>    Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
>    /sys/kernel/mm/hugepages/hugepages-16777216kB/nr_hugepages
>    write(0) failed: Invalid argument
>    [PASS]
> 
> Fixes: 27477b28b74f ("selftests/mm: hugepage_settings: add APIs to get and set nr_hugepages")
> Signed-off-by: Sayali Patil <sayalip@linux.ibm.com>
> ---
>  .../testing/selftests/mm/hugepage_settings.c  | 32 ++++++++++++++++++-
>  .../testing/selftests/mm/hugepage_settings.h  |  1 +
>  2 files changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/mm/hugepage_settings.c b/tools/testing/selftests/mm/hugepage_settings.c
> index 2eab2110ac6a..ce38ae3da01a 100644
> --- a/tools/testing/selftests/mm/hugepage_settings.c
> +++ b/tools/testing/selftests/mm/hugepage_settings.c
> @@ -422,6 +422,36 @@ static void hugetlb_sysfs_path(char *buf, size_t buflen,
>  		 size / 1024, attr);
>  }
>  
> +void hugetlb_write_num(const char *path, unsigned long num)
> +{
> +	int fd, saved_errno;
> +	ssize_t numwritten;
> +	char buf[21];
> +
> +	sprintf(buf, "%lu", num);
> +
> +	fd = open(path, O_WRONLY);
> +	if (fd == -1)
> +		ksft_exit_fail_msg("%s open failed: %s\n", path, strerror(errno));
> +
> +	numwritten = write(fd, buf, strlen(buf));
> +	saved_errno = errno;
> +	close(fd);
> +	errno = saved_errno;
> +
> +	/* Treat EINVAL as a skipped configuration (e.g., unsupported gigantic pages) */
> +	if (numwritten < 0 && errno == EINVAL) {
> +		ksft_print_msg("%s write(%s) failed: %s\n", path, buf, strerror(errno));

Should we even print anything here? Rather confusing. It's just like we cannot
allocate anything (no memory).

In general, you are copy-pasting a lot of write_num()+write_file() content,
which is really suboptimal.

All you want is an option for write_num -> write_file to skip on -EINVAL, correct?

There are not that many write_num / write_file users ...

-- 
Cheers,

David