linux-kernel - Re: [PATCH v2 2/2] mm: set pte writable while pte_soft_dirty() is true in do_swap

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Date: Mon, 10 Jun 2024 10:32:53 +0200
From: David Hildenbrand <david@...hat.com>
To: Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org,
 linux-mm@...ck.org
Cc: chrisl@...nel.org, kasong@...cent.com, linux-kernel@...r.kernel.org,
 minchan@...nel.org, ryan.roberts@....com, surenb@...gle.com,
 v-songbaohua@...o.com, willy@...radead.org
Subject: Re: [PATCH v2 2/2] mm: set pte writable while pte_soft_dirty() is
 true in do_swap_page()

On 07.06.24 23:13, Barry Song wrote:
> From: Barry Song <v-songbaohua@...o.com>
> 
> This patch leverages the new pte_needs_soft_dirty_wp() helper to optimize
> a scenario where softdirty is enabled, but the softdirty flag has already
> been set in do_swap_page(). In this situation, we can use pte_mkwrite
> instead of applying write-protection since we don't depend on write
> faults.
> 
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Barry Song <v-songbaohua@...o.com>
> ---
>   mm/memory.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index db9130488231..a063e489446d 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4322,7 +4322,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>   	if (!folio_test_ksm(folio) &&
>   	    (exclusive || folio_ref_count(folio) == 1)) {
>   		if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
> -		    !vma_soft_dirty_enabled(vma)) {
> +		    !pte_needs_soft_dirty_wp(vma, pte)) {
>   			pte = pte_mkwrite(pte, vma);
>   			if (vmf->flags & FAULT_FLAG_WRITE) {
>   				pte = pte_mkdirty(pte);

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

-- 
Cheers,

David / dhildenb