[Gllug] Linux 2.4.10 is out with better VM

[Christian Smith]

On Sat, 6 Oct 2001, Bruce Richardson wrote:

>On Sat, Oct 06, 2001 at 12:31:30AM +0100, David Irvine wrote:
>> I'd also be interested to know if they  have vixed the VM bugs since i'm
>> still contemplating going back to 2.2.18
>
>Make that 2.2.19, .18 has some issues.  Must say, 2.4.x seems to be
>taking much longer than 2.2.x did to settle down.  The difference
>between stable and development kernels seems to have blurred (from the
>stability point of view, anyway).  I suppose it's a legacy of 2.4's
>troubled gestation.

All a legacy of a VM system that was derived from the origional x86 model.
In VM terms, Linux is where 4.3BSD was, which had a VM system based on the
VAX, and generalised to try to make it 'portable' to other architectures.

4.4BSD took the sensible route, and threw out the old VM and imported a
new one from Mach. OpenBSD and NetBSD have gone one further, and created a
new VM system from scratch:
UVM - http://ccrc.wustl.edu/pub/chuck/tech/uvm/

What Linux should do, probably in 2.5 is simply rip out the existing VM,
and import a new VM or write one from scratch. They could do much worse
than using the UVM model. Unfortunately, I don't think the plans are that
radical, with current plan being to simply implement a reverse page
mapping. There is currently some hot debate on linux-mm whether reverse
mappings are worthwhile.

It has to be said that the Linux VM system is not as clean as either
BSD or SysV.

Is this stuff worth doing a GLLUG talk on? Would people be interested in
the VM architecture of various OSes?

Christian

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