Re: [Vserver] memory problems?

From: Roché Compaan <roche_at_upfrontsystems.co.za>
Date: Mon 12 Dec 2005 - 17:34:01 GMT
Message-Id: <1134408842.24153.19.camel@kwaaitjie>

On Mon, 2005-12-12 at 18:19 +0100, Herbert Poetzl wrote:
> On Mon, Dec 12, 2005 at 07:13:46PM +0200, Roché Compaan wrote:
> > On Mon, 2005-12-12 at 16:53 +0100, Herbert Poetzl wrote:
> > > On Mon, Dec 12, 2005 at 03:34:13PM +0200, Roché Compaan wrote:
> > > > On Mon, 2005-12-12 at 03:06 +0100, Herbert Poetzl wrote:
> > > > > On Sun, Dec 11, 2005 at 10:28:04PM +0200, Roché Compaan wrote:
> > > > > > On Sun, 2005-12-11 at 11:34 -0800, Alexander Kabanov wrote:
> > > > > > > hi,
> > > > > > >
> > > > > > > i'm having similar errors (I do have limits and scheduler set, using
> > > > > > > rlimits (as, rss, nproc) and scheduler) whenever i do stress testing,
> > > > > > > (overloading mta or web server for example).
> > > > > > >
> > > > > > > during a stress test, some applications die because of no memory
> > > > > > > available or can't fork, some stop with segmentation fault (not able
> > > > > > > to do vserver <vs> enter),. when attacking httpd might have httpd
> > > > > > > <defunct>.
> > > > > >
> > > > > > I am experiencing the same problems. The segfaults and not being able to
> > > > > > enter a vserver from the host *really* worries me.
> > > > >
> > > > > well, if the limits are reached, the guest can not create
> > > > > new processes and/or instantiate more memory ... of course
> > > > > this might lead to program termination and the fact that
> > > > > a guest cannot be entered (as the limits are hard limits).
> > > > > raising them will make it all work again ...
> > > >
> > > > If the vserver is hitting the limit then I'm less worried because I
> > > > can solve the problem by increasing the limit. I misread and thought
> > > > that there was plenty of memory to spare.
> > > >
> > > > Would I be right in assuming that increasing only the virtual memory
> > > > will solve the problem?
> > >
> > > probably that will solve 80% of the issues
> > > (see VM vs RSS hit ratio)
> >
> > Where?
>
> in the original email you sent (you removed the
> lines so I could not refer to them ...)

Ah, thanks.

>
> > > > I don't mind if virtual servers use swap space if they need memory
> > > > because we have plenty of disk space, but I don't want them to
> > > > consume all the physical memory on the box.
> > >
> > > trust me, you do mind as soon as the guests start
> > > swapping in and out ...
> >
> > Sorry, you'll have to explain - I don't understand how the vserver or
> > the linux kernel manages virtual memory or what you mean when you say
> > "swapping in and out".
>
> consider a total of 256 MB memory (RAM) on the host
> further, consider three guests with a memory footprint
> of 128MB RSS (means they need to have 128MB in memory
> to run, that's what Resident Set Size is), now they
> are alternating and will constantly swap in and out
> memory, because 3*128 > 256 ...

But what if I limit the sum of virtual server RSS limits to never exceed
the total RAM on the host as a rule, and make sure that there is enough
virtual memory for all of them? Ie. I have 4 GB RAM on the host and 4
vservers that each have a hard limit of 1 GB RSS and say triple the
virtual memory. Would I still get memory errors when vservers reach the
RSS limit, or only when they reach the VM limit?

-- 
Roché Compaan
Upfront Systems                   http://www.upfrontsystems.co.za
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