linux-kernel - Re: [PATCH 2/3] mm/khugepaged: use enum scan

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Message-ID: <B6AB9DAB-7985-44F0-A0D0-9FE77D3853B5@nvidia.com>
Date: Thu, 18 Dec 2025 10:54:30 -0500
From: Zi Yan <ziy@...dia.com>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>
Cc: "Garg, Shivank" <shivankg@....com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm/khugepaged: use enum scan_result for result
 variables

On 18 Dec 2025, at 4:17, David Hildenbrand (Red Hat) wrote:

> On 12/18/25 06:40, Garg, Shivank wrote:
>>
>>
>> On 12/16/2025 9:08 PM, Zi Yan wrote:
>>> On 16 Dec 2025, at 6:11, Shivank Garg wrote:
>>>
>>
>>>
>>>>   int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
>>>>   			    bool install_pmd)
>>>>   {
>>>
>>> And here.
>> Since this function is declared in khugepaged.h, I need to
>> move the enum definition to that header. I see two options for handling
>> the CONFIG_TRANSPARENT_HUGEPAGE check:
>>
>> 1. Define enum OUTSIDE the ifdef: This allows the static inline stub
>>     to also return enum scan_result, keeping the API consistent.
>> 2. Define enum INSIDE the ifdef: The enum is hidden when THP is disabled,
>>     forcing the stub to return int 0 instead.
>>
>> The only external caller (uprobes.c) of collapse_pte_mapped_thp currently
>> ignores the return value.
>
> Probably best to not expose that enum (especially when nobody cares ...) and instead expose a new void function for uprobe purposes.
>
> Maybe
>
> void collapse_pte_mapped_thp(...)
> {
> 	try_collapse_pte_mapped_thp();
> }
>
> Maybe something like that?

Sounds good to me.

Best Regards,
Yan, Zi