linux-kernel - Re: [PATCH v3 1/2] mm: huge_memory: disallow hugepages if the system-wide THP sysfs settings are disabled

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Message-ID: <44c805d7-000a-440e-995b-106f324eff15@redhat.com>
Date: Tue, 24 Jun 2025 10:29:57 +0200
From: David Hildenbrand <david@...hat.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
 hughd@...gle.com
Cc: ziy@...dia.com, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com,
 npache@...hat.com, ryan.roberts@....com, dev.jain@....com,
 baohua@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] mm: huge_memory: disallow hugepages if the
 system-wide THP sysfs settings are disabled

On 24.06.25 03:48, Baolin Wang wrote:
> 
> 
> On 2025/6/23 21:54, David Hildenbrand wrote:
>>
>>> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/
>>> selftests/mm/khugepaged.c
>>> index 4341ce6b3b38..85bfff53dba6 100644
>>> --- a/tools/testing/selftests/mm/khugepaged.c
>>> +++ b/tools/testing/selftests/mm/khugepaged.c
>>> @@ -501,11 +501,7 @@ static void __madvise_collapse(const char *msg,
>>> char *p, int nr_hpages,
>>>        printf("%s...", msg);
>>> -    /*
>>> -     * Prevent khugepaged interference and tests that MADV_COLLAPSE
>>> -     * ignores /sys/kernel/mm/transparent_hugepage/enabled
>>> -     */
>>> -    settings.thp_enabled = THP_NEVER;
>>> +    settings.thp_enabled = THP_ALWAYS;
>>
>>
>> Would MADVISE mode also work here? If we don't set MADV_HUGEPAGE, then
>> khugepaged should be excluded, correct?
> 
> I tried this, but some test cases failed. As I replied to Barry, it's
> because some tests previously set MADV_NOHUGEPAGE, and now there is no
> way to clear the MADV_NOHUGEPAGE flag except by setting MADV_HUGEPAGE.

Okay, can you add that detail to the patch description. I suspect we 
really want a way to undo what MADV_NOHUGEPAGE/MADV_NOHUGEPAGE did (if 
only naming wouldn't be complicated: MADV_DEFAULT_HUGEPAGE, hmmmm).

-- 
Cheers,

David / dhildenb