Re: [PATCH] mm: add a "struct page_frag" type containing a page,offset and length

[Ian Campbell]

On Thu, 2011-10-13 at 22:22 +0100, Andrew Morton wrote:
> Looks OK to me.  I'm surprised we don't already have such a thing.
> 
> Review comments:
> 
> 
> > +struct page_frag {
> > +	struct page *page;
> > +#if (BITS_PER_LONG > 32) || (PAGE_SIZE >= 65536)
> 
> It does add risk that people will add compile warnings and bugs by
> failing to consider or test the other case.
>
> We could reduce that risk by doing
> 
>    #if (PAGE_SIZE >= 65536)
> 
> but then the 32-bit version would hardly ever be tested at all.

Indeed. The first variant has the benefit that most 32-bit arches will
test one case and most 64-bit ones the other.

Perhaps the need to keep this struct small is not so acute as it is for
the skb_frag_t I nicked it from and just using __u32 unconditionally is
sufficient?

> 
> > +	__u32 page_offset;
> 
> I suggest this be called simply "offset".

ACK.

Thanks,

Ian.


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