Re: [dpdk-dev] very high VIRT memory usage

[Francesco <francesco.montorsi@gmail.com>]

Hi Anatoly,

Thanks a lot for the detailed response!
Good to know anyway there's a "fix" already done in 20.05... also because
I'm not interested in supporting secondary processes or having shared
memory...

Looking forward for the backports in stable branches then!

Thanks!
Francesco


Il mar 9 giu 2020, 14:46 Burakov, Anatoly <anatoly.burakov@intel.com> ha
scritto:

> On 08-Jun-20 12:03 PM, Francesco wrote:
> > Hi all,
> > I upgraded an old DPDK-based app which was using DPDK 17.11 to latest
> DPDK
> > 20.05 and I noticed that if I look  at "top" I see that the VIRT memory
> > taken by my application is now 256.1GB while before it was <1GB.
> >
> > I've seen this same behavior with also "testpmd" example... is this a
> known
> > issue with latest DPDK versions?
> > Can I tweak some setting to have VIRT memory usage more or less similar
> to
> > RSS ?
> >
> > I forgot to add I'm working on Linux, Centos7
> >
> > Thanks,
> > Francesco Montorsi
> >
>
> There was a discussion on this not too long ago, but i can't seem to
> find it for some reason. Anyway, long story short, that's not a bug,
> that's by design.
>
> Since 18.11 (or 18.05 to be precise), there is a new memory subsystem in
> DPDK that allows growing and shrinking DPDK memory usage at runtime.
> That means, you can start with zero hugepages preallocated, and then
> allocate as you go, letting the memory subsystem decide how much memory
> you need.
>
> The catch is that all of this hugepage memory is allocated into
> somewhere, some virtual address space. And *that* address space is
> preallocated at startup, to allow for secondary processes to duplicate
> primary process's address space exactly, and allow dynamic allocation of
> *shared* memory at runtime.
>
> This memory will show up in top et al. but the truth is, it's zero cost,
> because it's anonymous memory. It isn't actually taking up any RAM. It
> will show up in dumps (20.05 has already fixed that issue, and the fixes
> will probably be backported to stable, including 18.11), so unless you
> have a very specific problem, i don't think that's anything you should
> be concerned about.
>
> --
> Thanks,
> Anatoly
>