Observations on virtual memory operations

Pete Wright pete at nomadlogic.org
Mon Dec 28 23:37:13 UTC 2020

On 12/28/20 3:25 PM, doug wrote:
> I have two servers running jails that "routinely" run out of swapspace 
> with
> no demand paging activity. To try and get a handle on VM/swapspace
> management I have been tracking swapinfo vs memory use as measured by 
> top.
> The numbers do not exactly add up but I assume that is not involved in my
> issue.
> The other day I caught the system at 73% swapspace used. At this level 
> the
> system was in a near thrashing state in that typing a key got it 
> echoed in
> 10 <--> 30 seconds. There was about 600MB of swapspace at this point. I
> would think there is no way to debug this except as a thought experiment.

The first thing that comes to mind is do you have the ability to hook 
any metrics/monitoring onto this system.  For example, I use collectd on 
my systems to report overall CPU/memory metrics as well as per-process 
memory metrics.

Alternatively you could write a simple shell script that run's "ps" and 
parses the output of memory utilization on a per-process basis.

either of the above approaches should give you some insight into where 
the memory leak is coming from (assuming you already do not know).

one trick i use is to invoke a process with "limits" to ensure it does 
not exceed a certain amount of memory that I allocate to it. for example 
with firefox i do this:
$ limits -m 6g -v 6g /usr/local/bin/firefox

that should at least buy you enough time to investigate why the process 
needs so much memory and see what you can do about it.


Pete Wright
pete at nomadlogic.org

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