netdev - Re: [PATCH v3 4/7] net: Reorder the contents of skb_frag

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Message-ID: <20190724012828.GQ363@bombadil.infradead.org>
Date:   Tue, 23 Jul 2019 18:28:28 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Saeed Mahameed <saeedm@...lanox.com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "hch@....de" <hch@....de>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 4/7] net: Reorder the contents of skb_frag_t

On Tue, Jul 23, 2019 at 10:29:06PM +0000, Saeed Mahameed wrote:
> On Fri, 2019-07-12 at 06:43 -0700, Matthew Wilcox wrote:
> > From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> > 
> > Match the layout of bio_vec.
> > 
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> > ---
> >  include/linux/skbuff.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > index 7910935410e6..b9dc8b4f24b1 100644
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -314,8 +314,8 @@ struct skb_frag_struct {
> >  	struct {
> >  		struct page *p;
> >  	} page;
> > -	__u32 page_offset;
> >  	__u32 size;
> > +	__u32 page_offset;
> >  };
> >  
> 
> Why do you need this patch? this struct is going to be removed
> downstream eventually ..

If there's a performance regression, this is the perfect patch to include
as part of the bisection.  You'd think that this change could have no
effect, but I've seen weirder things.