linux-kernel - Re: [PATCH 1/3] mm/memory.c: Use folios in __copy_remote_vm

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Message-ID: <faa3d518-cd0f-4848-b4c7-deaad02bd0fd@redhat.com>
Date: Fri, 11 Jul 2025 12:49:25 +0200
From: David Hildenbrand <david@...hat.com>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>, linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 Jordan Rome <linux@...danrome.com>, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/3] mm/memory.c: Use folios in __copy_remote_vm_str()

On 09.07.25 21:40, Vishal Moola (Oracle) wrote:
> Use kmap_local_folio() instead of kmap_local_page().
> Replaces 2 calls to compound_head() from unmap_and_put_page() with one.
> 
> This prepares us for the removal of unmap_and_put_page().
> 
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
> ---
>   mm/memory.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 1174f3001307..d63f0d5abcc9 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -6815,6 +6815,7 @@ static int __copy_remote_vm_str(struct mm_struct *mm, unsigned long addr,
>   	while (len) {
>   		int bytes, offset, retval;
>   		void *maddr;
> +		struct folio *folio;
>   		struct page *page;
>   		struct vm_area_struct *vma = NULL;
>   
> @@ -6830,17 +6831,18 @@ static int __copy_remote_vm_str(struct mm_struct *mm, unsigned long addr,
>   			goto out;
>   		}
>   
> +		folio = page_folio(page);
>   		bytes = len;
>   		offset = addr & (PAGE_SIZE - 1);
>   		if (bytes > PAGE_SIZE - offset)
>   			bytes = PAGE_SIZE - offset;
>   
> -		maddr = kmap_local_page(page);
> +		maddr = kmap_local_folio(folio, folio_page_idx(folio, page) * PAGE_SIZE);

It's weird to go page -> folio -> page ... but maybe that's just the way 
it's supposed to work here ...

:)

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

-- 
Cheers,

David / dhildenb