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SubjectRe: [PATCH] TCP Zero Copy for mmapped files
   From: Alan Cox <>
Date: 02 Jan 2003 23:20:44 +0000

On Thu, 2003-01-02 at 22:28, Larry McVoy wrote:
> The VM cost hurts. Badly. Imagine that the network costs ZERO. Then
> the map/unmap/vm ops become the dominating term. That's why it is a
> fruitless approach, it still has a practical limit which is too low.

It depends how predictable your content is. With a 64bit box and a porn
server its probably quite tidy

Let's say you have infinite VM (which is what 64-bit almost is :) then
the cost is setting up all of these useless VMAs for each and every
file (which is a 1 time cost, ok), and also the VMA lookup each
write() call.

With sendfile() all of this goes straight to the page cache directly
without a VMA lookup.
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