Coda File System

Re: still a bit confused about the VM,memory,swap RVM issue

From: Jan Harkes <>
Date: Mon, 8 Nov 1999 22:11:17 -0500
On Fri, Nov 05, 1999 at 08:07:05PM -0500, Remo Strotkamp wrote:
> Hi there,
> But I am still a bit confused about the Virtual memory issue:
> somewhere is mentioned that you need at least the RVM size of Virtual
> memory! Now on my linux box, does this mean that I need as much swap
> and real memory as I have the size of RVM (i.e. the rvm data is
> shuffeled in the 'real mem +swap' space??)??? Or is the RVM used as
> some sort of swap directly???

An anonymous mmap is done for the size of the RVM data, which is then
read into this chunk of memory. For 1GB of RVM data you need at least
1GB of VM, which translates into at least 1GB swap space.

> So supposing I go for a 1GB RVM partition.
> Do I need 1GB minus real memory of swap????
> In any case this will create another problem, due to linux memory
> restrictions!!!!

Depending on how much memory other programs are using you might even
need more. Yes, we know that the memory restrictions are a serious
problem here, which is why we say that Coda doesn't yet scale well.

> Until 2.3.24I think the limit was 3GB of virtual memory.
> After 2.3.24 it goes into the terrabytes I think, but doesn't change
> anything,
> as probably nobody will put a developpment kernel on a fileserver! :-)

Even so, you need to find a big enough gap between the shared libraries
and other memory mapped things. And the fact that the data is completely
stored in both the rvm data file and on the swap, even if there are no
differences between the two isn't very nice either.

We're working on design changes that should improve things considerably,
in fact, Phil Nelson is about to start working on precisely these issues
during the next months.

Received on 1999-11-08 22:13:45