linux-kernel - Re: [PATCH v3 6/6] selftests: prctl: introduce tests for disabling THPs except for madvise

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Message-ID: <9bcb1dee-314e-4366-9bad-88a47d516c79@redhat.com>
Date: Tue, 5 Aug 2025 12:36:29 +0200
From: David Hildenbrand <david@...hat.com>
To: Usama Arif <usamaarif642@...il.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 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?

-- 
Cheers,

David / dhildenb