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

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Message-ID: <79fb5cb2-8a24-4260-a9e9-bdf2c5ef602f@amd.com>
Date: Thu, 18 Dec 2025 11:10:04 +0530
From: "Garg, Shivank" <shivankg@....com>
To: Zi Yan <ziy@...dia.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...nel.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 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.

What is the more preferred way for enum definition in such scenario?

Thanks,
Shivank

> In addition, the return types of find_pmd_or_thp_or_none(),
> hugepage_vma_revalidate(), alloc_charge_folio(), and check_pmd_state() need to be changed to enum scan_result too.
> 
> Best Regards,
> Yan, Zi