linux-kernel - Re: [PATCH v2 1/2] mm: khugepaged: convert set_huge

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Message-ID: <239471b5-12fe-4bad-a6e1-e9f0ad195ab5@redhat.com>
Date: Fri, 9 May 2025 16:58:23 +0200
From: David Hildenbrand <david@...hat.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
 willy@...radead.org
Cc: hannes@...xchg.org, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com,
 npache@...hat.com, ryan.roberts@....com, dev.jain@....com, ziy@...dia.com,
 vbabka@...e.cz, rppt@...nel.org, surenb@...gle.com, mhocko@...e.com,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mm: khugepaged: convert set_huge_pmd() to take a
 folio

> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index b04b6a770afe..aca66e7f4fd9 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1467,7 +1467,7 @@ static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot)
>   #ifdef CONFIG_SHMEM
>   /* hpage must be locked, and mmap_lock must be held */

^ that comment probably needs some love.

>   static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
> -			pmd_t *pmdp, struct page *hpage)
> +			pmd_t *pmdp, struct folio *folio)
>   {
>   	struct vm_fault vmf = {
>   		.vma = vma,
> @@ -1476,13 +1476,12 @@ static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
>   		.pmd = pmdp,
>   	};
>   
> -	VM_BUG_ON(!PageTransHuge(hpage));
>   	mmap_assert_locked(vma->vm_mm);
>   
> -	if (do_set_pmd(&vmf, hpage))
> +	if (do_set_pmd(&vmf, &folio->page))
>   		return SCAN_FAIL;
>   
> -	get_page(hpage);
> +	folio_get(folio);
>   	return SCAN_SUCCEED;
>   }
>   
> @@ -1689,7 +1688,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
>   maybe_install_pmd:
>   	/* step 5: install pmd entry */
>   	result = install_pmd
> -			? set_huge_pmd(vma, haddr, pmd, &folio->page)
> +			? set_huge_pmd(vma, haddr, pmd, folio)

Wondering why we are not passing in the folio+page pair in here as well. 
I assume in the foreseeable future this code will not be able to work 
with folios large than PMDs?

Apart from that LGTM.

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb