Re: Avoiding external fragmentation with a placement policyVersion 12

[David S. Miller]

From: "Martin J. Bligh" <mbligh@xxxxxxxxxx>
Date: Thu, 02 Jun 2005 22:34:42 -0700

> One of the calls I got the other day was for loopback interface. 
> Default MTU is 16K, which seems to screw everything up and do higher 
> order allocs. Turning it down to under 4K seemed to fix things. I'm 
> fairly sure loopback doesn't really need phys contig memory, but it 
> seems to use it at the moment ;-)

It helps get better bandwidth to have larger buffers.
That's why AF_UNIX tries to use larger orders as well.

With all these processors using prefetching in their
memcpy() implementations, reducing the number of memcpy()
calls per byte is getting more and more important.
Each memcpy() call makes you hit the memory latency
cost since the first prefetch can't be done early
enough.
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