Re: [PATCH v7 4/6] udmabuf: Convert udmabuf driver to use folios

[Matthew Wilcox <willy@infradead.org>]

On Mon, Dec 11, 2023 at 11:38:01PM -0800, Vivek Kasireddy wrote:
> @@ -42,7 +42,7 @@ static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
>  	if (pgoff >= ubuf->pagecount)
>  		return VM_FAULT_SIGBUS;
>  
> -	pfn = page_to_pfn(ubuf->pages[pgoff]);
> +	pfn = page_to_pfn(&ubuf->folios[pgoff]->page);

We have folio_pfn().

>  static int vmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
>  {
>  	struct udmabuf *ubuf = buf->priv;
> +	struct page **pages;
>  	void *vaddr;
> +	pgoff_t pg;
>  
>  	dma_resv_assert_held(buf->resv);
>  
> -	vaddr = vm_map_ram(ubuf->pages, ubuf->pagecount, -1);
> +	pages = kmalloc_array(ubuf->pagecount, sizeof(*pages), GFP_KERNEL);
> +	if (!pages)
> +		return -ENOMEM;
> +
> +	for (pg = 0; pg < ubuf->pagecount; pg++)
> +		pages[pg] = &ubuf->folios[pg]->page;
> +
> +	vaddr = vm_map_ram(pages, ubuf->pagecount, -1);
> +	kfree(pages);

We don't yet have a vm_map_ram() variant that takes an array of
folios.  We probably should; there was _something_ I was looking at
recently that would have liked it ...

> @@ -254,31 +262,70 @@ static int handle_shmem_pages(struct udmabuf *ubuf, struct file *memfd,
>  			      pgoff_t *pgbuf)
>  {
>  	pgoff_t pgidx, pgoff = offset >> PAGE_SHIFT;
> -	struct page *page;
> +	struct folio *folio = NULL;
>  
>  	for (pgidx = 0; pgidx < pgcnt; pgidx++) {
> -		page = shmem_read_mapping_page(memfd->f_mapping,
> -					       pgoff + pgidx);
> -		if (IS_ERR(page))
> -			return PTR_ERR(page);
> +		folio = shmem_read_folio(memfd->f_mapping,
> +					 pgoff + pgidx);

You could join these two lines.