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

[Sayali Patil <sayalip@linux.ibm.com>]

On 30/06/26 16:15, David Hildenbrand (Arm) wrote:
> 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 ...
> 

Hi David,

Yes, all I need is to ignore the expected -EINVAL when attempting to
configure gigantic hugepages via nr_hugepages.

I looked at extending write_num()/write_file() for this as in v1
(https://lore.kernel.org/all/8bfa921e30eb94072685103f6496784aa23bb166.1782365671.git.sayalip@linux.ibm.com/),
but these helpers are shared by several other selftests.
For example, write_file() is used by split_huge_page_test setup and by
khugepaged tests for drop_caches, and is also used for various THP and
khugepaged settings where -EINVAL would indicate a genuine setup
failure. This concern was also raised during the v1 review.

Because the expected -EINVAL is specific to gigantic hugepage runtime
allocation, I kept the handling local to the hugetlb setup path rather
than changing the semantics of the common helpers.

I also agree that printing a message is not particularly useful in this
case, and we can simply return without emitting any output.

Please let me know if you would prefer a different approach.

Thanks,
Sayali