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From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH 2/2] udp: RCU handling for Unicast packets.
Date: Thu, 30 Oct 2008 00:05:55 -0700 (PDT)
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From: Eric Dumazet <dada1@cosmosbay.com>
Date: Thu, 30 Oct 2008 08:04:42 +0100

> If we design something that could be reused, say for TCP sockets, we need
> to be able to handle very large number of 'NULL' pointers, say, up to 64*1024*1024
> 
> So lets use the low order bit, set to one for "NULL" pointers, and 0 for regular pointers.
> 
> This gives us 31 bits (or 63 bits) to store any valuable info :)
> 
> and all ...._nulls() macros would not need to know the max value (UDP_HTABLE_SIZE in UDP case),
> since all they have to do is a test ((unsigned long)pos & 1)
> 
> At iterator exit, pos would contain the 'index' value, (pos >> 1), to hide this
> implementation detail.

This sound fine to me.  Quite an improvement in fact :)