[Beowulf] first cluster

Rahul Nabar rpnabar at gmail.com
Thu Jul 15 21:30:17 PDT 2010

On Thu, Jul 15, 2010 at 8:29 PM, Mark Hahn <hahn at mcmaster.ca> wrote:
> yes.  actually, configuring memory and swap is an interesting topic.
> the feature Chris is referring to is, I think, the vm.overcommit_memory
> sysctl (and the associated vm.overcommit_ratio.)  every distro I've seen
> leaves these at the default seting: vm.overcommit_memory=0.  this is

Is it possible to know how much over-committed my OS was, say in the
last one day. Or at least instantaneously. I want to see how good or
bad my user apps have been at requesting memory. Thus, if I were to
take the strict approach of memory assignment I can know in advance if
or not a lot of malloc calls are going to get a zero returned.

> basically the traditional setting that tells the kernel to feel free
> to allocate way too much memory, and to resolve memory crunches via OOM
> killing.  obviously, this isn't great, since it never tells apps to conserve
> memory (malloc returning zero), and often kills processes that
> you're rather not be killed (sshd, other system daemons).  on clusters

Ah! this might explain why once in a while I have a node with sshd
dead. Is it possible to tell the kernel that certain processes are
"privileged" and when it seeks to find random processes to kill it
should not select these "privileged" processes? Some candidates that
come to my mind are sshd, nagios and pbs_mom


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