linux-kernel - Re: [RFC PATCH 1/2] mm/khugepaged: Convert __collapse_huge_page

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Message-ID: <fd2149bb-2c5f-222c-5134-ae251910b3cc@redhat.com>
Date:   Mon, 25 Sep 2023 09:18:40 +0200
From:   David Hildenbrand <david@...hat.com>
To:     "Vishal Moola (Oracle)" <vishal.moola@...il.com>,
        linux-mm@...ck.org
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] mm/khugepaged: Convert
 __collapse_huge_page_isolate() to use folios

On 22.09.23 21:36, Vishal Moola (Oracle) wrote:
> This is in preparation for the removal of the khugepaged compound_pagelist.
> 
> Replaces 11 calls to compound_head() with 1, and removes 499 bytes of
> kernel text.
> 
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
> ---
>   mm/khugepaged.c | 52 ++++++++++++++++++++++++-------------------------
>   1 file changed, 26 insertions(+), 26 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 88433cc25d8a..f46a7a7c489f 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -541,7 +541,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
>   					struct collapse_control *cc,
>   					struct list_head *compound_pagelist)
>   {
> -	struct page *page = NULL;
> +	struct folio *folio = NULL;
>   	pte_t *_pte;
>   	int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
>   	bool writable = false;
> @@ -570,15 +570,15 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
>   			result = SCAN_PTE_UFFD_WP;
>   			goto out;
>   		}
> -		page = vm_normal_page(vma, address, pteval);
> -		if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
> +		folio = vm_normal_folio(vma, address, pteval);
> +		if (unlikely(!folio) || unlikely(folio_is_zone_device(folio))) {
>   			result = SCAN_PAGE_NULL;
>   			goto out;
>   		}
>   
> -		VM_BUG_ON_PAGE(!PageAnon(page), page);
> +		VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio);
>   
> -		if (page_mapcount(page) > 1) {
> +		if (folio_estimated_sharers(folio) > 1) {

For a tail page of a PTE-mapped THP this is not the same.

The possible side effects this might have should be spelled out in the 
patch description.

-- 
Cheers,

David / dhildenb