PERFORCE change 129544 for review

[Sam Leffler]

Robert Watson wrote:
>
> On Mon, 26 Nov 2007, Kip Macy wrote:
>
>> http://perforce.freebsd.org/chv.cgi?CH=129544
>>
>> Change 129544 by kmacy at kmacy:storage:toestack on 2007/11/26 05:26:43
>>
>>     disable merging of data into existing mbufs if
>>     new SB_TOE flag is set
>
> One of the reasons we compact socket buffers with TCP and other stream 
> protocols is that if you're dealing with an application/protocol that 
> spits out data in small chunks (i.e., a series of printfs) and nagel 
> is disabled, you end up with a series of packets that make quite 
> inefficient use of mbufs, as the space wasted per chunk of data is 
> significant.  Not only that, we bill for space in socket buffers based 
> on the space held by the full mbuf, not just the data in the mbuf when 
> it comes to socket buffer resource limits, so you can rapidly fill up 
> socket buffer limits without compaction in this type of scenario.  I'm 
> not sure which protocols this would affect, but I'd imagine that 
> RPC-like protocols supporting asynchronous operation (so that you get 
> a series of replies and responses in flight at once) might be 
> relevant, such as IMAP.
>
> On an unrelated not, if we want a non-coalescing modes for socket 
> bufferss, we should probably also give it a name like "SB_NOCOALESCE" 
> rather than something TOE-specific.

There used to be a record boundary indication to inhibit coalescing.

    Sam