linux-kernel - Re: [ofa-general] [PATCH 2.6.30] RDMA/cxgb3: Remove modulo math.

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Message-ID: <49931C9D.2090604@opengridcomputing.com>
Date:	Wed, 11 Feb 2009 12:44:45 -0600
From:	Steve Wise <swise@...ngridcomputing.com>
To:	Roland Dreier <rdreier@...co.com>
CC:	randy.dunlap@...cle.com, linux-next@...r.kernel.org,
	linux-kernel@...r.kernel.org, general@...ts.openfabrics.org
Subject: Re: [ofa-general] [PATCH 2.6.30] RDMA/cxgb3: Remove modulo math.

Roland Dreier wrote:
>  > > Is it possible for the page to be bigger than 4GB?  If so then yes you
>  > > might be chopping off high-order bits or something.
>
>  > Yes it is possible.
>  > 
>  > A MR can be created with an iov_base of say 0xffffffff00000000.
>  > 
>  > Then any sge.addr entries would be the iob_base + any offset.
>
> But the code we're talking about is:
>
> 		/* to in the WQE == the offset into the page */
> 		wqe->recv.sgl[i].to = cpu_to_be64(((u32) wr->sg_list[i].addr) %
> 				(1UL << (12 + page_size[i])));
>
> so it seems the top address bits don't matter unless page_size[i] is at
> least 20 -- in which case using 1UL to shift overflows on 32 bits anyway...
>
>   

Yes yes...you're right.   This code is really just saving the offset in 
a page.

I'll send a new patch.

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