linux-kernel - Re: [PATCH mm-new 2/2] mm/khugepaged: merge PTE scanning logic into a new helper

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Message-ID: <0d55d763-81ff-4b99-bb13-3dbb9af53cdc@arm.com>
Date: Fri, 3 Oct 2025 22:35:12 +0530
From: Dev Jain <dev.jain@....com>
To: Lance Yang <lance.yang@...ux.dev>, akpm@...ux-foundation.org,
 david@...hat.com, lorenzo.stoakes@...cle.com
Cc: ziy@...dia.com, baolin.wang@...ux.alibaba.com, Liam.Howlett@...cle.com,
 npache@...hat.com, ryan.roberts@....com, baohua@...nel.org,
 ioworker0@...il.com, richard.weiyang@...il.com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH mm-new 2/2] mm/khugepaged: merge PTE scanning logic into a
 new helper


On 02/10/25 1:02 pm, Lance Yang wrote:
> From: Lance Yang <lance.yang@...ux.dev>
>
> As David suggested, the PTE scanning logic in hpage_collapse_scan_pmd()
> and __collapse_huge_page_isolate() was almost duplicated.
>
> This patch cleans things up by moving all the common PTE checking logic
> into a new shared helper, thp_collapse_check_pte().
>
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Lance Yang <lance.yang@...ux.dev>
> ---
>   

In hpage_collapse_scan_pmd(), we enter with mmap lock held, so for
an anonymous vma, is it even possible to hit if (!folio_test_anon(folio))?
In which case we can replace this with VM_BUG_ON_FOLIO and abstract away
till the folio_maybe_mapped_shared() block?