On 6/30/26 22:20, Sayali Patil wrote:
>
>
> 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 <[email protected]>
>>> ---
>>> .../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.saya...@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.
We can either convert the functions to use flags, or hide it in some internal
helpers, like the following:
>From 1b1b8ad51f1f0be469cb191736300254b9521fe4 Mon Sep 17 00:00:00 2001
From: "David Hildenbrand (Arm)" <[email protected]>
Date: Wed, 1 Jul 2026 10:45:16 +0200
Subject: [PATCH] tmp
Signed-off-by: David Hildenbrand (Arm) <[email protected]>
---
tools/testing/selftests/mm/vm_util.c | 28 ++++++++++++++++++++++++----
tools/testing/selftests/mm/vm_util.h | 1 +
2 files changed, 25 insertions(+), 4 deletions(-)
diff --git a/tools/testing/selftests/mm/vm_util.c
b/tools/testing/selftests/mm/vm_util.c
index 311fc5b4513eb..362070f817e9b 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -719,7 +719,8 @@ int read_file(const char *path, char *buf, size_t buflen)
return (unsigned int) numread;
}
-void write_file(const char *path, const char *buf, size_t buflen)
+static int __write_file(const char *path, const char *buf, size_t buflen,
+ bool ignore_einval)
{
int fd, saved_errno;
ssize_t numwritten;
@@ -735,14 +736,23 @@ void write_file(const char *path, const char *buf, size_t
buflen)
saved_errno = errno;
close(fd);
errno = saved_errno;
- if (numwritten < 0)
+
+ if (numwritten < 0) {
+ if (ignore_einval && errno == EINVAL)
+ return;
ksft_exit_fail_msg("%s write(%.*s) failed: %s\n", path,
(int)(buflen - 1),
buf, strerror(errno));
+ }
if (numwritten != buflen - 1)
ksft_exit_fail_msg("%s write(%.*s) is truncated, expected %zu
bytes, got %zd bytes\n",
path, (int)(buflen - 1), buf, buflen - 1,
numwritten);
}
+static void write_file(const char *path, const char *buf, size_t buflen)
+{
+ __write_file(path, bug, buflen, /* ignore_einval = */ false);
+}
+
unsigned long read_num(const char *path)
{
char buf[21];
@@ -753,12 +763,22 @@ unsigned long read_num(const char *path)
return strtoul(buf, NULL, 10);
}
-void write_num(const char *path, unsigned long num)
+static void __write_num(const char *path, unsigned long num, bool
ignore_einval)
{
char buf[21];
sprintf(buf, "%lu", num);
- write_file(path, buf, strlen(buf) + 1);
+ write_file(path, buf, strlen(buf) + 1, ignore_einval);
+}
+
+void write_num(const char *path, unsigned long num)
+{
+ return __write_num(path, num, /* ignore_einval = */ false);
+}
+
+void write_num_ignore_einval(const char *path, unsigned long num)
+{
+ return __write_num(path, num, /* ignore_einval = */ true);
}
static unsigned long shmall, shmmax;
diff --git a/tools/testing/selftests/mm/vm_util.h
b/tools/testing/selftests/mm/vm_util.h
index ea8fc8fdf0eb0..7799154b67eed 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -168,6 +168,7 @@ void write_file(const char *path, const char *buf, size_t
buflen);
int read_file(const char *path, char *buf, size_t buflen);
unsigned long read_num(const char *path);
void write_num(const char *path, unsigned long num);
+void write_num_ignore_einval(const char *path, unsigned long num);
void shm_limits_prepare(unsigned long length);
void __shm_limits_restore(void);
--
2.43.0
--
Cheers,
David
