[PATCH v2 4/6] drm/pagemap: Allocate folios when possible

[Matthew Brost]

On Fri, Jul 25, 2025 at 05:39:28PM +0200, Francois Dugast wrote:
> If the order is greater than zero, allocate a folio when populating the
> RAM PFNs instead of allocating individual pages one after the other. For
> example if 2MB folios are used instead of 4KB pages, this reduces the
> number of calls to the allocation API by 512.
> 
> v2:
> - Use page order instead of extr argument (Matthew Brost)
> - Allocate with folio_alloc() (Matthew Brost)
> - Loop for mpages and free_pages based on order (Matthew Brost)
> 
> Signed-off-by: Francois Dugast <francois.dugast at intel.com>
> Cc: Matthew Brost <matthew.brost at intel.com>
> ---
>  drivers/gpu/drm/drm_pagemap.c | 38 ++++++++++++++++++++++++++---------
>  1 file changed, 28 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
> index b6f5d3a8e445..38753ce2bca7 100644
> --- a/drivers/gpu/drm/drm_pagemap.c
> +++ b/drivers/gpu/drm/drm_pagemap.c
> @@ -458,54 +458,72 @@ static int drm_pagemap_migrate_populate_ram_pfn(struct vm_area_struct *vas,
>  {
>  	unsigned long i;
>  
> -	for (i = 0; i < npages; ++i, addr += PAGE_SIZE) {
> +	for (i = 0; i < npages;) {
>  		struct page *page, *src_page;
> +		unsigned int order;
> +		struct folio *folio;
>  
>  		if (!(src_mpfn[i] & MIGRATE_PFN_MIGRATE))
> -			continue;
> +			goto next;
>  
>  		src_page = migrate_pfn_to_page(src_mpfn[i]);
>  		if (!src_page)
> -			continue;
> +			goto next;
>  
>  		if (fault_page) {
>  			if (src_page->zone_device_data !=
>  			    fault_page->zone_device_data)
> -				continue;
> +				goto next;
>  		}
>  
> +		order = folio_order(page_folio(src_page));
> +
> +		/* TODO: Support fallback to single pages if THP allocation fails */
>  		if (vas)
> -			page = alloc_page_vma(GFP_HIGHUSER, vas, addr);
> +			folio = vma_alloc_folio(GFP_HIGHUSER, order, vas, addr);
>  		else
> -			page = alloc_page(GFP_HIGHUSER);
> +			folio = folio_alloc(GFP_HIGHUSER, order);

I haven't checked but I assume if order == 0, then alloc_page_vma ==
vma_alloc_folio? So goes for alloc_page / folio_alloc. If so, then this
looks good.

>  
> -		if (!page)
> +		if (!folio)
>  			goto free_pages;
>  
> +		page = folio_page(folio, 0);
>  		mpfn[i] = migrate_pfn(page_to_pfn(page));
> +
> +next:
> +		addr += page_size(page);
> +		i += NR_PAGES(order);
>  	}
>  
> -	for (i = 0; i < npages; ++i) {
> +	for (i = 0; i < npages;) {
>  		struct page *page = migrate_pfn_to_page(mpfn[i]);
> +		unsigned int order;

unsigned int order = 0;

>  
>  		if (!page)
>  			continue;

s/continue/goto next;


>  
>  		WARN_ON_ONCE(!trylock_page(page));
> -		++*mpages;
> +
> +		order = folio_order(page_folio(page));

next:

> +		*mpages += NR_PAGES(order);
> +		i += NR_PAGES(order);
>  	}
>  
>  	return 0;
>  
>  free_pages:
> -	for (i = 0; i < npages; ++i) {
> +	for (i = 0; i < npages;) {

Same logic changes to this loop as the one above.

Matt

>  		struct page *page = migrate_pfn_to_page(mpfn[i]);
> +		unsigned int order;
>  
>  		if (!page)
>  			continue;
>  
>  		put_page(page);
>  		mpfn[i] = 0;
> +
> +		order = folio_order(page_folio(page));
> +		i += NR_PAGES(order);
>  	}
>  	return -ENOMEM;
>  }
> -- 
> 2.43.0
>