Re: [PATCH v2 4/6] mm: memory: use a folio in do_cow_page()

[Vishal Moola]

On Mon, Nov 13, 2023 at 11:22:20PM +0800, Kefeng Wang wrote:
> Use folio_prealloc() helper and convert to use a folio in
> do_cow_page(), which save five compound_head() calls.

s/do_cow_page()/do_cow_fault()/

Aside from that,
Reviewed-by: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> ---
>  mm/memory.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index d85df1c59f52..f350ab2a324f 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4653,6 +4653,7 @@ static vm_fault_t do_read_fault(struct vm_fault *vmf)
>  static vm_fault_t do_cow_fault(struct vm_fault *vmf)
>  {
>  	struct vm_area_struct *vma = vmf->vma;
> +	struct folio *folio;
>  	vm_fault_t ret;
>  
>  	ret = vmf_can_call_fault(vmf);
> @@ -4661,16 +4662,11 @@ static vm_fault_t do_cow_fault(struct vm_fault *vmf)
>  	if (ret)
>  		return ret;
>  
> -	vmf->cow_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vmf->address);
> -	if (!vmf->cow_page)
> +	folio = folio_prealloc(vma->vm_mm, vma, vmf->address, false);
> +	if (!folio)
>  		return VM_FAULT_OOM;
>  
> -	if (mem_cgroup_charge(page_folio(vmf->cow_page), vma->vm_mm,
> -				GFP_KERNEL)) {
> -		put_page(vmf->cow_page);
> -		return VM_FAULT_OOM;
> -	}
> -	folio_throttle_swaprate(page_folio(vmf->cow_page), GFP_KERNEL);
> +	vmf->cow_page = &folio->page;
>  
>  	ret = __do_fault(vmf);
>  	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
> @@ -4679,7 +4675,7 @@ static vm_fault_t do_cow_fault(struct vm_fault *vmf)
>  		return ret;
>  
>  	copy_user_highpage(vmf->cow_page, vmf->page, vmf->address, vma);
> -	__SetPageUptodate(vmf->cow_page);
> +	__folio_mark_uptodate(folio);
>  
>  	ret |= finish_fault(vmf);
>  	unlock_page(vmf->page);
> @@ -4688,7 +4684,7 @@ static vm_fault_t do_cow_fault(struct vm_fault *vmf)
>  		goto uncharge_out;
>  	return ret;
>  uncharge_out:
> -	put_page(vmf->cow_page);
> +	folio_put(folio);
>  	return ret;
>  }
>  
> -- 
> 2.27.0