Monitoring Samba's memory usage: A cautionary tale

[Richard Sharpe]

On Wed, Feb 3, 2016 at 11:53 AM, Christof Schmitt <cs at samba.org> wrote:
>
> On Wed, Feb 03, 2016 at 10:22:06AM -0800, Richard Sharpe wrote:
> > Hi folks,
> >
> > We spent a lot of time recently trying to understand Samba's memory usage
> > and the incremental cost of an additional smbd. This was sparked by the
> > fact that we had a couple of memory leaks in our VFS module.
> >
> > After we fixed the memory leaks we then spent an enormous amount of time
> > down in the weeds because top and ps are not actually good tools for this.
> > Specifically, they overstate the RSS size by including the text segments of
> > all the shared libraries used.
> >
> > See, for example, this page:
> > http://virtualthreads.blogspot.com/2006/02/understanding-memory-usage-on-linux.html
> >
> > I still have not found the best tool for this, but you can use pmap and
> > process the output to exclude all TDBs (because there will only be one copy
> > of them in memory and thus they should count once) and the text regions of
> > all shared libraries (all RO memory segments.)
> >
> > I hope this saves some people some time and also dispels the view held by
> > some that Samba is a memory hog.
> >
> > Also, you can check for heap growth by looking at the size of the memory
> > segment just before the stack. If that is constantly growing, you probably
> > have a problem.
>
> There is a feature in Linux to display the "Proportional Segment Size":
>
> https://www.kernel.org/doc/Documentation/filesystems/proc.txt
>
>   The "proportional set size" (PSS) of a process is the count of pages it has
>   in memory, where each page is divided by the number of processes sharing it.
>   So if a process has 1000 pages all to itself, and 1000 shared with one other
>   process, its PSS will be 1500.
>
> A web search also finds a tool that uses this information:
> https://www.selenic.com/smem/
>
> In theory, this should give accurate memory usage information, but i
> have not checked it extensively.

That looks like an awesome tool. Thanks.


-- 
Regards,
Richard Sharpe
(何以解憂？唯有杜康。--曹操)