linux-kernel - Re: [PATCH v5 6/7] selftests: prctl: introduce tests for disabling THPs completely

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Message-ID: <5560e517-aa26-4693-baf7-e618bec3c5fa@gmail.com>
Date: Mon, 18 Aug 2025 11:43:35 +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 v5 6/7] selftests: prctl: introduce tests for disabling
 THPs completely



On 18/08/2025 10:36, David Hildenbrand wrote:
>> +
>> +TEST_F(prctl_thp_disable_completely, fork)
>> +{
>> +    int ret = 0;
>> +    pid_t pid;
>> +
>> +    /* Make sure prctl changes are carried across fork */
>> +    pid = fork();
>> +    ASSERT_GE(pid, 0);
>> +
>> +    if (!pid)
>> +        prctl_thp_disable_completely_test(_metadata, self->pmdsize, variant->thp_policy);
>> +
> 
> Skimming over this once more ... this raises two questions
> 
> (a) There is nothing to wait for in the child
> (b) Does it work when we return in the child from this function?
> 
> I think (b) works by design of the kselftest_harness, as this function is
> itself executed from a child process.
> 
> Regarding (a), it might be cleaner to just
> 

Makes sense, thanks for pointing this out! Have sent the fixlets.