Date: Mon, 17 Jun 2024 18:52:54 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
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Subject: Re: [PATCH net-next v12 05/13] page_pool: convert to use netmem

On 6/13/24 02:35, Mina Almasry wrote:
> Abstrace the memory type from the page_pool so we can later add support
> for new memory types. Convert the page_pool to use the new netmem type
> abstraction, rather than use struct page directly.
> 
> As of this patch the netmem type is a no-op abstraction: it's always a
> struct page underneath. All the page pool internals are converted to
> use struct netmem instead of struct page, and the page pool now exports
> 2 APIs:
> 
> 1. The existing struct page API.
> 2. The new struct netmem API.

nits below,

Reviewed-by: Pavel Begunkov <asml.silence@...il.com>


> Keeping the existing API is transitional; we do not want to refactor all
> the current drivers using the page pool at once.
> 
> The netmem abstraction is currently a no-op. The page_pool uses
> page_to_netmem() to convert allocated pages to netmem, and uses
> netmem_to_page() to convert the netmem back to pages to pass to mm APIs,
> 
> Follow up patches to this series add non-paged netmem support to the
> page_pool. This change is factored out on its own to limit the code
> churn to this 1 patch, for ease of code review.
> 
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
>   #endif /* _NET_NETMEM_H */
> diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
> index 873631c79ab16..5e129d5304f53 100644
> --- a/include/net/page_pool/helpers.h
> +++ b/include/net/page_pool/helpers.h
> @@ -55,6 +55,8 @@
>   #include <linux/dma-mapping.h>
>   
>   #include <net/page_pool/types.h>
> +#include <net/net_debug.h>
> +#include <net/netmem.h>
>   
>   #ifdef CONFIG_PAGE_POOL_STATS
>   /* Deprecated driver-facing API, use netlink instead */
> @@ -103,7 +105,7 @@ static inline struct page *page_pool_dev_alloc_pages(struct page_pool *pool)
>    * Get a page fragment from the page allocator or page_pool caches.
>    *
>    * Return:
> - * Return allocated page fragment, otherwise return NULL.
> + * Return allocated page fragment, otherwise return 0.

It's a page_pool_dev_alloc_frag()'s comment, and the function
still returns a pointer.

...
>   static inline void *page_pool_alloc_va(struct page_pool *pool,
> @@ -172,7 +174,8 @@ static inline void *page_pool_alloc_va(struct page_pool *pool,
>   	struct page *page;
>   
>   	/* Mask off __GFP_HIGHMEM to ensure we can use page_address() */
> -	page = page_pool_alloc(pool, &offset, size, gfp & ~__GFP_HIGHMEM);
> +	page = netmem_to_page(
> +		page_pool_alloc(pool, &offset, size, gfp & ~__GFP_HIGHMEM));
>   	if (unlikely(!page))
>   		return NULL;
>   
> @@ -189,7 +192,7 @@ static inline void *page_pool_alloc_va(struct page_pool *pool,
>    * it returns va of the allocated page or page fragment.
>    *
>    * Return:
> - * Return the va for the allocated page or page fragment, otherwise return NULL.
> + * Return the va for the allocated page or page fragment, otherwise return 0.

ditto

>    */
>   static inline void *page_pool_dev_alloc_va(struct page_pool *pool,
>   					   unsigned int *size)
> @@ -212,6 +215,11 @@ page_pool_get_dma_dir(const struct page_pool *pool)
>   	return pool->p.dma_dir;
>   }
>   
> +static inline void page_pool_fragment_netmem(netmem_ref netmem, long nr)
> +{
> +	atomic_long_set(&netmem_to_page(netmem)->pp_ref_count, nr);
> +}
...

-- 
Pavel Begunkov

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