Observations on virtual memory operations

[Pete Wright]

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.
>
<snip>
>
> 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.

-p

-- 
Pete Wright
pete at nomadlogic.org
@nomadlogicLA