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Message-ID: <00842b4663291b0523bb203740d23f74@quanstro.net>
From: erik quanstrom <quanstro@quanstro.net>
Date: Fri,  5 May 2006 10:41:57 -0500
To: 9fans@cse.psu.edu
Subject: Re: [9fans] kernel development: how not to
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sort of.  it's an extension.  here's the kerneltrap summary:

	http://kerneltrap.org/node/6506

what linux actually said is that COW games (e.g. for freebsd's zero-copy
socket code) are worse than just copying the data.

the real difference between bsd's stuff and what linus did is
the linux trick is an explict system call, not a vm game.
but he misses that adding strange system calls that parallel
read and write is even bigger trouble.  either your fundamental
object is a file (unix) or a block of memory (multix).  pick a
lane!  certainly don't mix the two at the same level.

linus may be right that the freebsd vm's techniques are broken.
i don't know.

the zero-copy idea is tantalizing.  it would be neat to allow the
network stacks or devdraw to live in a user-level fileserver
without a performance (2 copy) penalty.  but it may be the case
that allowing this trickery is more code than it is worth.

- erik

On Fri May  5 10:20:1CDT 2006, leimy2k@gmail.com wrote:
> Is the the vmslice that Linus told BSD people they were a bunch of
> retards for not having?
> 
> 
> 
> On 5/5/06, erik quanstrom <quanstro@quanstro.net> wrote:
> > the linux guys decided to implement system calls
> > "splice" and "tee".  splice concatinates the pages from
> > two files -- the vm equivalent of "cat a b".  tee
> > is the vm equivalent of its namesake.
> >
> >         http://lwn.net/Articles/181169/#Comments
> >
> > the best part is the conclusion -- "needs a bit more work".
> > ha!
> >
> > - erik