On 05/08/2025 11:36, David Hildenbrand wrote:

On 04.08.25 17:40, Usama Arif wrote:

quoted

The test will set the global system THP setting to never, madvise
or always depending on the fixture variant and the 2M setting to
inherit before it starts (and reset to original at teardown)

This tests if the process can:
- successfully set and get the policy to disable THPs expect for madvise.
- get hugepages only on MADV_HUGE and MADV_COLLAPSE if the global policy
   is madvise/always and only with MADV_COLLAPSE if the global policy is
   never.
- successfully reset the policy of the process.
- after reset, only get hugepages with:
   - MADV_COLLAPSE when policy is set to never.
   - MADV_HUGE and MADV_COLLAPSE when policy is set to madvise.
   - always when policy is set to "always".
- repeat the above tests in a forked process to make sure  the policy is
   carried across forks.

Signed-off-by: Usama Arif <redacted>
---

[...]

quoted

+FIXTURE_VARIANT(prctl_thp_disable_except_madvise)
+{
+    enum thp_enabled thp_policy;
+};
+
+FIXTURE_VARIANT_ADD(prctl_thp_disable_except_madvise, never)
+{
+    .thp_policy = THP_NEVER,
+};
+
+FIXTURE_VARIANT_ADD(prctl_thp_disable_except_madvise, madvise)
+{
+    .thp_policy = THP_MADVISE,
+};
+
+FIXTURE_VARIANT_ADD(prctl_thp_disable_except_madvise, always)
+{
+    .thp_policy = THP_ALWAYS,
+};
+
+FIXTURE_SETUP(prctl_thp_disable_except_madvise)
+{
+    if (!thp_available())
+        SKIP(return, "Transparent Hugepages not available\n");
+
+    self->pmdsize = read_pmd_pagesize();
+    if (!self->pmdsize)
+        SKIP(return, "Unable to read PMD size\n");

Should we test here if the kernel knows PR_THP_DISABLE_EXCEPT_ADVISED, and if not, skip?

Might be as simple as trying issuing two prctl, and making sure the first disabling attempt doesn't fail. If so, SKIP.

Nothing else jumped at me. Can you include a test run result in the patch description?

Instead of 2 prctls, I think doing just the below should be enough:

diff --git a/tools/testing/selftests/mm/prctl_thp_disable.c b/tools/testing/selftests/mm/prctl_thp_disable.c
index 93cedaa59854..da28bc4441ed 100644
--- a/tools/testing/selftests/mm/prctl_thp_disable.c
+++ b/tools/testing/selftests/mm/prctl_thp_disable.c

@@ -236,6 +236,9 @@ FIXTURE_SETUP(prctl_thp_disable_except_madvise)
        if (!self->pmdsize)
                SKIP(return, "Unable to read PMD size\n");
 
+       if (prctl(PR_SET_THP_DISABLE, 1, PR_THP_DISABLE_EXCEPT_ADVISED, NULL, NULL))
+               SKIP(return, "Unable to set PR_THP_DISABLE_EXCEPT_ADVISED\n");
+
        thp_save_settings();
        thp_read_settings(&self->settings);
        self->settings.thp_enabled = variant->thp_policy;

Will include the test run result in the last patch description. Just adding it here as well:

./prctl_thp_disable
TAP version 13
1..12
# Starting 12 tests from 6 test cases.
#  RUN           prctl_thp_disable_completely.never.nofork ...
#            OK  prctl_thp_disable_completely.never.nofork
ok 1 prctl_thp_disable_completely.never.nofork
#  RUN           prctl_thp_disable_completely.never.fork ...
#            OK  prctl_thp_disable_completely.never.fork
ok 2 prctl_thp_disable_completely.never.fork
#  RUN           prctl_thp_disable_completely.madvise.nofork ...
#            OK  prctl_thp_disable_completely.madvise.nofork
ok 3 prctl_thp_disable_completely.madvise.nofork
#  RUN           prctl_thp_disable_completely.madvise.fork ...
#            OK  prctl_thp_disable_completely.madvise.fork
ok 4 prctl_thp_disable_completely.madvise.fork
#  RUN           prctl_thp_disable_completely.always.nofork ...
#            OK  prctl_thp_disable_completely.always.nofork
ok 5 prctl_thp_disable_completely.always.nofork
#  RUN           prctl_thp_disable_completely.always.fork ...
#            OK  prctl_thp_disable_completely.always.fork
ok 6 prctl_thp_disable_completely.always.fork
#  RUN           prctl_thp_disable_except_madvise.never.nofork ...
#            OK  prctl_thp_disable_except_madvise.never.nofork
ok 7 prctl_thp_disable_except_madvise.never.nofork
#  RUN           prctl_thp_disable_except_madvise.never.fork ...
#            OK  prctl_thp_disable_except_madvise.never.fork
ok 8 prctl_thp_disable_except_madvise.never.fork
#  RUN           prctl_thp_disable_except_madvise.madvise.nofork ...
#            OK  prctl_thp_disable_except_madvise.madvise.nofork
ok 9 prctl_thp_disable_except_madvise.madvise.nofork
#  RUN           prctl_thp_disable_except_madvise.madvise.fork ...
#            OK  prctl_thp_disable_except_madvise.madvise.fork
ok 10 prctl_thp_disable_except_madvise.madvise.fork
#  RUN           prctl_thp_disable_except_madvise.always.nofork ...
#            OK  prctl_thp_disable_except_madvise.always.nofork
ok 11 prctl_thp_disable_except_madvise.always.nofork
#  RUN           prctl_thp_disable_except_madvise.always.fork ...
#            OK  prctl_thp_disable_except_madvise.always.fork
ok 12 prctl_thp_disable_except_madvise.always.fork
# PASSED: 12 / 12 tests passed.
# Totals: pass:12 fail:0 xfail:0 xpass:0 skip:0 error:0