[dpdk-users] Should ''shmget" not be used to consume hugepages in DPDK?

[Byonggon Chun]

> shmget is a legacy Unix API and there is no point in using it.

Yeah, I agree with it,
I also prefer to use mmap with hugetlbfs in a DPDK container.

The reason why I started this mail thread is some DPDK users still use
shmget to consume hugepages, and I just wanted to find a good rationale to
convince them to use mmap.

But, at this point, I have only one rationale : shmget is a legacy UINIX
API.

On Fri, Dec 20, 2019 at 6:06 AM Stephen Hemminger <
stephen at networkplumber.org> wrote:

> On Fri, 20 Dec 2019 01:23:50 +0900
> Byonggon Chun <byonggonchun at gmail.com> wrote:
>
> > Hi all.
> > I'm Kubernetes contributors and I'm working to make container isolation
> of
> > hugepages that allows us to set hugepages limit per container cgroup.
> > (At this point, limits are set on pod level cgroup even though we asked
> > hugepages as the container level resource)
> >
> > I tore down testPMD and some parts of DPDK lib and I got a question
> after i
> > found there is no usage of "shmget" in DPDK.
> >
> > My question is that Should "shmget" not be used to consume hugepages in
> > DPDK?
> > And here is following questions:
> > 1) If we don't have to use "shmget", Why? Does it affect performance?
> > 2) If I use "shmget" to get hugepages, should I call "mlock" syscall for
> it?
> >
> > For more details, as I know there are three ways to consume hugepages in
> > kubernetes.
> > 1) shmget with SHM_HUGETLB
> > 2) mmap with hugetlbs filebacking
> > 3) mmap with MAP_ANONYMOUS | MAP_HUGETLB
> >
> > And I found that testPMD calls mlock syscall when it maps an anonymous
> > hugepages or external allocated hugepages.
> >
> https://github.com/DPDK/dpdk/blob/924e55fb340623f03fdf2ff7fbcfd78819d1db25/app/test-pmd/testpmd.c#L896
> >
> https://github.com/DPDK/dpdk/blob/924e55fb340623f03fdf2ff7fbcfd78819d1db25/app/test-pmd/testpmd.c#L916
> >
> > Thanks.
>
> shmget is a legacy Unix API and there is no point in using it.
> For new applications libhugetlbfs is preferable.
>