[TUHS] Charles Forsyth on putting Unix on a diet.

Larry McVoy lm at mcvoy.com
Fri Oct 27 03:27:35 AEST 2017


On Tue, Oct 24, 2017 at 10:51:17PM -0400, Dan Cross wrote:
> I've always enjoyed this paper; recently I found occasion to thumb
> through it again. I thought I'd pass it on; I'm curious what some on
> the list think about this given their first-hand knowledge of relevant
> history (Larry, I'm looking at you; especially with respect his
> comments on the VM system).
> 
>         - Dan C.
> 
> http://www.terzarima.net/doc/taste.pdf

OK, I've read it.  This could have been a great paper if he had included
some performance results.  As it is, I'm sorry that his ideas didn't take
hold, or at least get some discussion.

The paging stuff is neat but it doesn't address the file system page cache
so far as I tell.  It's process based so unless the process had the file
mmap-ed it wouldn't take care of it.  And mmap didn't exist at the time,
so I'm not sure how he handed the page cache.  

He was fixated on code size, and yeah, on 4MB machines, you need to
be even on 8 you need to be (at Sun we called EMACS Eight Megs And
Constantly Swapping).  But I'd like to know if his paging scheme worked.
I went through a period where I wrote over a dozen different pageout
daemons in an effort to do a better job; none did.  They had certain
use cases where they did better but then other work loads made them
perform worse.  That global pageout daemon is still around, it's
depressingly hard to do better than that.  If he succeeded it would
be nice to have numbers.

His pageout scheme could have all forward pointers if he had them in
the vnode along with the process.

I agree with him on fork, there is no reason not do do vfork in fork
that I can think of (other than wnj's hack of putting stats in the 
parent process by the child in csh and that was just gross).

His comments on the file system switch vs VFS sort of miss the point
that the VFS was put in place to allow file systems that don't have
Unix semantics (NFS being the biggest example).  But I agree that 
there perhaps could have been a better approach, this is why it 
would have been nice to have his stuff get a broader audience.

I disagree on the streams/STREAMS stuff, that shit has no place in
anything that wants performance.  I'm working with netflix, trying
to do better than this:

https://news.ycombinator.com/item?id=15367421

which is a discussion of their writeup of how they managed to push
~100Gbit/sec of movies on a single machine.  Sticking STREAMS in the
middle of that was a bad idea back in the day and a worse idea today.

But all in all, an interesting paper.  It's pretty amazing how many of
the people in the references I know, lots of them I've worked with, Steve
Kleiman was my mentor at Sun, Rosenthal and I had tons of OS discussions.
I toyed with going to HP Labs to work with John Wilkes, etc.  Definitely
a trip down memory lane and makes me feel super lucky to have gotten to
work with people of that caliber.

Thanks for the pointer.

--lm


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