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

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 09-Jun-20 2:13 PM, Ferruh Yigit wrote:
> On 6/9/2020 1:46 PM, Burakov, Anatoly wrote:
>> 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.
> 
> Can it be "Big spike in DPDK VSZ" ?
> http://inbox.dpdk.org/dev/CAGxAMwD6Wtfi=C2Txwjfk0zhFvRzeqBu7mFfE8ayh=EJi2aU-A@mail.gmail.com/#t
> 

Yes, that's the one, thanks Ferruh :)

>> 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