Re: [Vserver] RSS vs. AS, and swap.

From: Herbert Poetzl <>
Date: Thu 12 Jan 2006 - 02:38:25 GMT
Message-ID: <>

On Wed, Jan 11, 2006 at 04:38:58PM -0800, Robin Lee Powell wrote:
> I want my VServer to not be able to choke my real server by using up
> all the RAM, so I set an RSS limitation. As you can see, it's not
> working very well:
> PROC: 72 142 -1 0
> VM: 104883 223551 -1 0
> VML: 0 0 -1 0
> RSS: 56597 131072 131072 356

well, as we see it is working very well ...

hard limit is hard limit, so once you reach it, game
over for the the processes consuming memory ...

> The problem I'm having is that instead of swapping things out,
> processes simply get killed, even when there's lots of swap left.

as I explained many times (here and on IRC) you do
not really want a swap-out behaviour, but once again
here is a simple example ...

just consider 10 guests, all set to 128MB of 'memory'
and the same amount as 'swap' ... now let's assume
the guests are slightly above the memory limit, because
the customer (as usual) pushes the limits and uses
roughly 200MB of memory+swap ...

what will happen on a box with 3GB of ram in this
case? it will trash to death, because all 10 guests
would continuously swap in and out stuff, while the
system memory is half free ... and all guests could
live and run quite well on that machine ...

> So, I'm wondering:
> What do RSS and AS actually *mean* when applied to the whole
> VServer?

RSS means Resident Set Size (i.e. the amount of
memory which is actually 'present' in RAM), and AS
means Adress Space, which is an artificial limit
which 'could' be compared to swap space, but does
not necessarily end up in swap ...

> Is fork_rss on be default? If so, how do I turn it off?

should not be on by default, unless that changed
recently ...

> How do I limit RAM usage on the VServer *and* let it use up swap
> before it starts killing things?

the real solution will be (a to be implemented)
soft limit for RSS, which basically penalizes the
guest for being over the limit, but does not do
the very expensive swapping, unless the memory is
really low, in which case memory of guests which
are over limit get preference to the swapout ...

for now, I would suggest to do what you actually
said, and use the RSS hard limit for preventing
customers from using up all your memory ...
(i.e. make it large enough so that it doesn't
hurt the friendly customer, but small enough, so
that your system will keep running when somebody
is excessive)


> Thanks!
> -Robin
> --
> ***
> Reason #237 To Learn Lojban: "Homonyms: Their Grate!"
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Received on Thu Jan 12 02:40:23 2006

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