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Message-ID: <5dc09930-e137-47ba-a98f-416d3319c8be@gmail.com>
Date: Tue, 5 Aug 2025 13:19:32 +0100
From: Usama Arif <usamaarif642@...il.com>
To: David Hildenbrand <david@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc: linux-fsdevel@...r.kernel.org, corbet@....net, rppt@...nel.org,
surenb@...gle.com, mhocko@...e.com, hannes@...xchg.org, baohua@...nel.org,
shakeel.butt@...ux.dev, riel@...riel.com, ziy@...dia.com,
laoar.shao@...il.com, dev.jain@....com, baolin.wang@...ux.alibaba.com,
npache@...hat.com, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com,
ryan.roberts@....com, vbabka@...e.cz, jannh@...gle.com,
Arnd Bergmann <arnd@...db.de>, sj@...nel.org, linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH v3 6/6] selftests: prctl: introduce tests for disabling
THPs except for madvise
On 05/08/2025 11:36, David Hildenbrand wrote:
> On 04.08.25 17:40, Usama Arif wrote:
>> 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 <usamaarif642@...il.com>
>> ---
>
> [...]
>
>> +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
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