Re: [PATCH] mm/memory.c: avoid repeated set_page_dirty in fault_dirty_shared_page

[David Hildenbrand <david@redhat.com>]

On 12.12.19 16:21, Li Xinhai wrote:
> When vm_ops->page_mkwrite is defined, and called from wp_page_shared and
> do_shared_fault, the set_page_dirty must already called by page_mkwrite.
> Then in fault_dirty_shared_page, avoid this repeated call.
> 
> Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
> Cc: Jan Kara <jack@suse.cz>
> ---
>  mm/memory.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 606da18..34a83d7 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2300,10 +2300,11 @@ static vm_fault_t fault_dirty_shared_page(struct vm_fault *vmf)
>  	struct vm_area_struct *vma = vmf->vma;
>  	struct address_space *mapping;
>  	struct page *page = vmf->page;
> -	bool dirtied;
> +	bool dirtied = false;
>  	bool page_mkwrite = vma->vm_ops && vma->vm_ops->page_mkwrite;
>  
> -	dirtied = set_page_dirty(page);
> +	if(!page_mkwrite)
> +		dirtied = set_page_dirty(page);
>  	VM_BUG_ON_PAGE(PageAnon(page), page);
>  	/*
>  	 * Take a local copy of the address_space - page.mapping may be zeroed
> @@ -3645,7 +3646,7 @@ static vm_fault_t do_shared_fault(struct vm_fault *vmf)
>  	 * Check if the backing address space wants to know that the page is
>  	 * about to become writable
>  	 */
> -	if (vma->vm_ops->page_mkwrite) {
> +	if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
>  		unlock_page(vmf->page);
>  		tmp = do_page_mkwrite(vmf);
>  		if (unlikely(!tmp ||
> 

This hunk looks like an unrelated change to me.

-- 
Thanks,

David / dhildenb