Possible working method to get actual process size on Linux

[Stefan Reich]

Hi Stefan,

thanks for the hint. It hopefully won't block longer than it takes to read
the file, no?

It does appear to take a bit to do that, I'm seeing ~ .25 s for cat
/proc/.../smaps > dev/null

Greetings,
Stefan

On Thu, 3 Oct 2019 at 15:01, Stefan Karlsson <stefan.karlsson at oracle.com>
wrote:

> Hi Stefan,
>
> On 2019-10-03 12:19, Stefan Reich wrote:
> > I'm still trying to get Linux to report a correct process size when using
> > ZGC (the memory multi-mapping issue).
> >
> > My idea is to parse /proc/pid/smaps.
>
> I'd like to point out that reading this file will most likely block the
> entire process from making progress. We've seen instances where reading
> this file caused the application and JVM to stand still for multiple
> seconds. If your applications are latency sensitive you'd probably want
> to avoid doing this.
>
> Cheers,
> StefanK
>
>
>   Sadly, I can't see physical addresses
> > there, only virtual ones. So I group by virtual address range. Here's
> what
> > I got for an example process with is reported by top as 2.7 GB:
> >
> > Address range 000000xxxxxxxxxx: 6 MB
> > Address range 000004xxxxxxxxxx: 38 MB
> > Address range 000007xxxxxxxxxx: 646 MB
> > Address range 000008xxxxxxxxxx: 38 MB
> > Address range 00000bxxxxxxxxxx: 631 MB
> > Address range 000010xxxxxxxxxx: 38 MB
> > Address range 000013xxxxxxxxxx: 690 MB
> > Address range 00007fxxxxxxxxxx: 726 MB
> >
> > It appears I have to discount the 07, 0b and 13 ranges to get to a
> > reasonable actual process size of 844 MB.
> >
> > Question: Are these address ranges fixed or does ZGC choose different
> ones
> > depending on heap size? Where exactly do the address ranges begin and
> end?
> >
> > As soon as this reporting method works, let's publish it as a standard
> tool
> > for anyone using ZGC on Linux. I can't be the only one who's driven nuts
> by
> > not knowing how big my processes are.
> >
> > Greetings,
> > Stefan
> >
>


-- 
Stefan Reich
BotCompany.de // Java-based operating systems