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

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Message-Id: <20111013142201.355f9afc.akpm@linux-foundation.org>
Date:	Thu, 13 Oct 2011 14:22:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
Cc:	rientjes@...gle.com, ian.campbell@...rix.com,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	jaxboe@...ionio.com, linux-mm@...ck.org
Subject: Re: [PATCH] mm: add a "struct page_frag" type containing a page,
 offset and length

On Thu, 13 Oct 2011 16:51:48 -0400 (EDT)
David Miller <davem@...emloft.net> wrote:

> >> 
> >> http://patchwork.ozlabs.org/patch/118693/
> >> http://patchwork.ozlabs.org/patch/118694/
> >> http://patchwork.ozlabs.org/patch/118695/
> >> http://patchwork.ozlabs.org/patch/118700/
> >> http://patchwork.ozlabs.org/patch/118696/
> >> http://patchwork.ozlabs.org/patch/118699/
> >> 
> >> This is a replacement for patch #1 in that series.
> >> 
> > 
> > Ok, let's add Andrew to the thread so this can go through -mm in 
> > preparation for that series.
> 
> It doesn't usually work like that, net-next is usually one of the first
> trees that Stephen pulls into -next, so this kind of simple dependency should
> go into my tree

yup.

> if the -mm developers give it an ACK and are OK with it.

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.

> +	__u32 page_offset;

I suggest this be called simply "offset".

> +	__u32 size;
> +#else
> +	__u16 page_offset;
> +	__u16 size;
> +#endif
> +};
> 	
> 
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