Re: [PATCH 1/9] mm: add a "struct subpage" type containing a page, offset and length

Re: [PATCH 1/9] mm: add a "struct subpage" type containing a page, offset and length

[Ian Campbell]

(reposting including LKML to catch other potential users)

Is this structure of any use to unify other instances of a similar
tuple, e.g. biovec, pagefrag etc?

Ian.

On Mon, 2011-10-10 at 12:11 +0100, Ian Campbell wrote:
> A few network drivers currently use skb_frag_struct for this purpose but I have
> patches which add additional fields and semantics there which these other uses
> do not want.
> 
> A structure for reference sub-page regions seems like a generally useful thing
> so do so instead of adding a network subsystem specific structure.
> 
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Cc: linux-mm@kvack.org
> ---
>  include/linux/mm_types.h |   11 +++++++++++
>  1 files changed, 11 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 774b895..dc1d103 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -135,6 +135,17 @@ struct page {
>  #endif
>  ;
>  
> +struct subpage {
> +	struct page *page;
> +#if (BITS_PER_LONG > 32) || (PAGE_SIZE >= 65536)
> +	__u32 page_offset;
> +	__u32 size;
> +#else
> +	__u16 page_offset;
> +	__u16 size;
> +#endif
> +};
> +
>  typedef unsigned long __nocast vm_flags_t;
>  
>  /*