Re: [dpdk-dev] Reg 6Wind fastpath DPDK 18.11.1 virtual memory allocation ( 54.5GB of anonymous mapping)

[Olivier Matz <olivier.matz@6wind.com>]

Hi Shanmugasundaram,

On Wed, Jun 09, 2021 at 01:46:35PM +0100, Bruce Richardson wrote:
> On Wed, Jun 09, 2021 at 02:28:04PM +0200, David Marchand wrote:
> > On Wed, Jun 9, 2021 at 2:02 PM Shanmugasundaram M <shansirtt@gmail.com> wrote:
> > > We are using  6Wind fastpath(fp-rte) which is using DPDK version 18.11.1.
> > > We are seeing  65.5G(preallocated during startup) of virtual memory for
> > > fp-rte on a 32GB machine, 10G of that was huge pages (5000 mappings of 2M.)
> > >
> > > We found 4 strange anon (4K size) segments totaling 54.5G (16+16+16+6.5).
> > > Note: we changed / customized memory CONFIG_RTE_MAX_MEMSEG_PER_LIST=24576
> > > and default value of  CONFIG_RTE_MAX_MEMSEG_LISTS=64 used.
> > > Kindly let us know
> > > 1. Why are allocating  54.5 GB anonymous mapping
> > > 2. When will we use it ?
> > 
> > This is likely pre-reserved virtual memory from the DPDK allocator.
> > This virtual memory won't probably never be used.
> > 
> 
> There may not be actually any memory backing this, since DPDK will reserve
> huge amounts of virtual address space without actually using it. So those
> GB's you see in the virtual memory may be completely unused, the addresses
> are just reserved to ensure that if memory does need to be mapped into the
> process, we have an appropriate contiguous address block to put it in.
> 
> > But you'd better ask 6WIND guys as they maintain their own DPDK downstream.
> > 
> > Copying a few guys.

I agree with David and Bruce. This is probably related to virtual memory
areas reserved by eal_get_virtual_area() (mmap of /dev/zero). Enabling EAL
debug logs should show traces about it.

If you need support (even on old 6WINDGate versions based on
dpdk-18.11), please open a ticket at 6WIND support, we'll be happy to
help.

Regards,
Olivier