Subject: Re: [PATCH v2] mm: page_frag: Warn_on when frag_alloc size is bigger than PAGE_SIZE

From: Jakub Kicinski <[email-masked]>
Date: Mon, 30 May 2022 12:29:18 -0700

On Mon, 30 May 2022 12:27:05 -0700 Jakub Kicinski wrote:
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e008a3df0485..360a545ee5e8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5537,6 +5537,7 @@ EXPORT_SYMBOL(free_pages);
>   * sk_buff->head, or to be used in the "frags" portion of skb_shared_info.
>   */
>  static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
> +					     unsigned int fragsz,
>  					     gfp_t gfp_mask)
>  {
>  	struct page *page = NULL;
> @@ -5549,7 +5550,7 @@ static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
>  				PAGE_FRAG_CACHE_MAX_ORDER);
>  	nc->size = page ? PAGE_FRAG_CACHE_MAX_SIZE : PAGE_SIZE;
>  #endif
> -	if (unlikely(!page))
> +	if (unlikely(!page && fragsz <= PAGE_SIZE))
>  		page = alloc_pages_node(NUMA_NO_NODE, gfp, 0);
>  
>  	nc->va = page ? page_address(page) : NULL;
> @@ -5576,7 +5577,7 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
>  
>  	if (unlikely(!nc->va)) {
>  refill:
> -		page = __page_frag_cache_refill(nc, gfp_mask);
> +		page = __page_frag_cache_refill(nc, fragsz, gfp_mask);
>  		if (!page)
>  			return NULL;

Oh, well, the reuse also needs an update. We can slap a similar
condition next to the pfmemalloc check.