Re: [dpdk-dev] rte_mempool_create fails with ENOMEM

[Stephen Hemminger <stephen@networkplumber.org>]

You can reserve hugepages on the kernel cmdline (GRUB).

On Fri, Dec 19, 2014 at 12:13 PM, Newman Poborsky <newman555p@gmail.com>
wrote:

> On Thu, Dec 18, 2014 at 9:03 PM, Ananyev, Konstantin <
> konstantin.ananyev@intel.com> wrote:
>
> >
> >
> > > -----Original Message-----
> > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Ananyev,
> Konstantin
> > > Sent: Thursday, December 18, 2014 5:43 PM
> > > To: Newman Poborsky; dev@dpdk.org
> > > Subject: Re: [dpdk-dev] rte_mempool_create fails with ENOMEM
> > >
> > > Hi
> > >
> > > > -----Original Message-----
> > > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Newman Poborsky
> > > > Sent: Thursday, December 18, 2014 1:26 PM
> > > > To: dev@dpdk.org
> > > > Subject: [dpdk-dev] rte_mempool_create fails with ENOMEM
> > > >
> > > > Hi,
> > > >
> > > > could someone please provide any explanation why sometimes mempool
> > creation
> > > > fails with ENOMEM?
> > > >
> > > > I run my test app several times without any problems and then I start
> > > > getting ENOMEM error when creating mempool that are used for packets.
> > I try
> > > > to delete everything from /mnt/huge, I increase the number of huge
> > pages,
> > > > remount /mnt/huge but nothing helps.
> > > >
> > > > There is more than enough memory on server. I tried to debug
> > > > rte_mempool_create() call and it seems that after server is restarted
> > free
> > > > mem segments are bigger than 2MB, but after running test app for
> > several
> > > > times, it seems that all free mem segments have a size of 2MB, and
> > since I
> > > > am requesting 8MB for my packet mempool, this fails.  I'm not really
> > sure
> > > > that this conclusion is correct.
> > >
> > > Yes,rte_mempool_create uses  rte_memzone_reserve() to allocate
> > > single physically continuous chunk of memory.
> > > If no such chunk exist, then it would fail.
> > > Why physically continuous?
> > > Main reason - to make things easier for us, as in that case we don't
> > have to worry
> > > about situation when mbuf crosses page boundary.
> > > So you can overcome that problem like that:
> > > Allocate max amount of memory you would need to hold all mbufs in worst
> > case (all pages physically disjoint)
> > > using rte_malloc().
> >
> > Actually my wrong: rte_malloc()s wouldn't help you here.
> > You probably need to allocate some external (not managed by EAL) memory
> in
> > that case,
> > may be mmap() with MAP_HUGETLB, or something similar.
> >
> > > Figure out it's physical mappings.
> > > Call  rte_mempool_xmem_create().
> > > You can look at: app/test-pmd/mempool_anon.c as a reference.
> > > It uses same approach to create mempool over 4K pages.
> > >
> > > We probably add similar function into mempool API
> > (create_scatter_mempool or something)
> > > or just add a new flag (USE_SCATTER_MEM) into rte_mempool_create().
> > > Though right now it is not there.
> > >
> > > Another quick alternative - use 1G pages.
> > >
> > > Konstantin
> >
>
>
> Ok, thanks for the explanation. I understand that this is probably an OS
> question more than DPDK, but is there a way to again allocate a contiguous
> memory for n-th run of my test app?  It seems that hugepages get
> divded/separated to individual 2MB hugepage. Shouldn't OS's memory
> management system try to group those hupages back to one contiguous chunk
> once my app/process is done?   Again, I know very little about Linux memory
> management and hugepages, so forgive me if this is a stupid question.
> Is rebooting the OS the only way to deal with this problem?  Or should I
> just try to use 1GB hugepages?
>
> p.s. Konstantin, sorry for the double reply, I accidentally forgot to
> include dev list in my first reply  :)
>
> Newman
>
> >
> > > >
> > > > Does anybody have any idea what to check and how running my test app
> > > > several times affects hugepages?
> > > >
> > > > For me, this doesn't make any since because after test app exits,
> > resources
> > > > should be freed, right?
> > > >
> > > > This has been driving me crazy for days now. I tried reading a bit
> more
> > > > theory about hugepages, but didn't find out anything that could help
> > me.
> > > > Maybe it's something else and completely trivial, but I can't figure
> it
> > > > out, so any help is appreciated.
> > > >
> > > > Thank you!
> > > >
> > > > BR,
> > > > Newman P.
> >
>