linux-kernel - Re: [PATCH v5 7/7] selftests: prctl: introduce tests for disabling THPs except for madvise

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Message-ID: <cdd753ab-61b7-48ac-b535-556f39f46b81@redhat.com>
Date: Mon, 18 Aug 2025 15:06:00 +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 v5 7/7] selftests: prctl: introduce tests for disabling
 THPs except for madvise

On 15.08.25 15:54, 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).
> The fixture setup will also test if PR_SET_THP_DISABLE prctl call can
> be made with PR_THP_DISABLE_EXCEPT_ADVISED and skip if it fails.
> 
> This tests if the process can:
> - successfully 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".
> - never get a THP with MADV_NOHUGEPAGE.
> - repeat the above tests in a forked process to make sure  the policy is
>    carried across forks.
> 
> Test results:
> ./prctl_thp_disable
> TAP version 13
> 1..12
> ok 1 prctl_thp_disable_completely.never.nofork
> ok 2 prctl_thp_disable_completely.never.fork
> ok 3 prctl_thp_disable_completely.madvise.nofork
> ok 4 prctl_thp_disable_completely.madvise.fork
> ok 5 prctl_thp_disable_completely.always.nofork
> ok 6 prctl_thp_disable_completely.always.fork
> ok 7 prctl_thp_disable_except_madvise.never.nofork
> ok 8 prctl_thp_disable_except_madvise.never.fork
> ok 9 prctl_thp_disable_except_madvise.madvise.nofork
> ok 10 prctl_thp_disable_except_madvise.madvise.fork
> ok 11 prctl_thp_disable_except_madvise.always.nofork
> ok 12 prctl_thp_disable_except_madvise.always.fork
> 
> Signed-off-by: Usama Arif <usamaarif642@...il.com>
> ---

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers

David / dhildenb