netdev - Re: [PATCH]: Fix sk_buff page offsets and lengths.

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Message-ID: <20070731140054.GA11442@2ka.mipt.ru>
Date:	Tue, 31 Jul 2007 18:00:55 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	sfr@...b.auug.org.au, shemminger@...ux-foundation.org
Subject: Re: [PATCH]: Fix sk_buff page offsets and lengths.

On Tue, Jul 31, 2007 at 01:23:29PM +0100, Christoph Hellwig (hch@...radead.org) wrote:
> On Tue, Jul 31, 2007 at 02:20:51PM +0400, Evgeniy Polyakov wrote:
> > On Mon, Jul 30, 2007 at 06:50:28PM -0700, David Miller (davem@...emloft.net) wrote:
> > > 
> > > Stephen Rothwell pointed out to me that the skb_frag_struct
> > > is broken on platforms using 64K or larger page sizes, it
> > > even generates warnings when (for example) the myri10ge driver
> > > tries to assign PAGE_SIZE into frag->size.
> > > 
> > > I've thus increased page offset and size to __u32 in the patch below.
> > 
> > Maybe wrap it into 
> > #if PAGE_OFFSET > 12
> > #endif
> > 
> > or something like that?
> > 
> > I'm not sure actually why drivers would want to have list of 64k pages,
> > instead driver could call give_me_pages(size) instead of alloc_pages 
> > and per-arch allocator would return one page or set of pages. This is a
> > handwaving for now...
> 
> What about sendfile/splice on hugetlbfs?

offset in tcp_sendpage() ends up being poffset % PAGE_SIZE,
page is 
struct page *page = pages[poffset / PAGE_SIZE];

So, as far as I understand, it will split bigpage into PAGE_SIZEd
chunks.

-- 
	Evgeniy Polyakov
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