On Fri, 31 Mar 2000, Rik van Riel wrote:
> On Fri, 31 Mar 2000, Marco Colombo wrote:
>
> > On the other side, you know most of the processes you're going to run
> > have a large address spaces but a small working-sets. Here your VM is
> > mostly swap, so suppose you have 64MB of RAM and 256MB of swap.
> > On sych a system, RAM is used always as a kind of cache, for process pages.
> > (Of course, it's used as a cache for FS blocks, too).
> > If you let processes allocate more that 256MB of VM, you're reducing
> > the cache size, and effectiveness. On such a system it makes sense
> > NOT to include RAM in the VM counts (just like you don't include RAM
> > in counts for available disk space...).
>
> Indeed. We _need_ memory for the kernel and for caching of
> executables. Maybe we should reserve something like
> min(ram_size / 2, swap_size / 2) for kernel memory and
> cache...
Speaking of reserving memory...
how difficult is to implement a configurable upper limit for total VM?
Something like: /proc/sys/vm/total_VM
Just setting it, the admin could tune memory reservation, or turn on
wild overcommitting:
echo "1024M" > /proc/sys/vm/total_VM
on a 64MB+256MB system *will* overcommit.
echo "256M" > /proc/sys/vm/total_VM
will reserve 64MB of RAM for caching (and kernel internal) purposes.
total_VM should be of course the sum of all address spaces of all
processes + kernel.
Address spaces mapped with mmap(..., MAP_SHARED, PROT_READ, ...)
from files should not be counted (no real VM gets allocated to them,
RAM is used again as a cache for file data).
Reserving space for kernel usage is done anyway by the low-watermark
limit... and AFAIK, the kernel address space can't be swapped.
>
> regards,
>
> Rik
> --
> The Internet is not a network of computers. It is a network
> of people. That is its real strength.
>
> Wanna talk about the kernel? irc.openprojects.net / #kernelnewbies
> http://www.conectiva.com/ http://www.surriel.com/
>
.TM.
--
____/ ____/ /
/ / / Marco Colombo
___/ ___ / / Technical Manager
/ / / ESI s.r.l.
_____/ _____/ _/ Colombo@ESI.it
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