[dpdk-users] rte_segments: hugepages are not in contiguous memory

[Sergio Gonzalez Monroy]

On 04/10/2016 09:00, Renata Saiakhova wrote:
> Hi all,
>
> I'm using dpdk 16.04 (I tried 16.07 with the same results) and linux 
> kernel 4.4.20 in a virtual machine (I'm using libvirt framework). I 
> pass a parameter in kernel command line to allocate 512 hugepages of 2 
> MB at boot time. They are successfully allocated. When an application 
> with dpdk starts it calls rte_pktmbuf_pool_create() which in turns 
> requests internally 649363712 bytes.  Those bytes should be allocated 
> from one of rte_memseg. rte_memsegs describes contiguous portions of 
> memory (both physical and virtual) built on hugepages. This allocation 
> fails, because there are no rte_memsegs of this size (or bigger). 
> Further debugging shows that hugepages are allocated in non-contiguous 
> physical memory and therefore rte_memsegs are built respecting gaps in 
> physical memory.
> Below are the sizes of segments built on hugepages (in bytes)
> 2097152
> 6291456
> 2097152
> 524288000
> 2097152
> 532676608
> 2097152
> 2097152
> So there are 5 segments which includes only one hugepage!
> This behavior is completely different to what I observe with linux 
> kernel 3.8 (used with the same application with dpdk) - where all 
> hugepages are allocated in contiguous memory.
> Does anyone experience the same issue? Could it be some kernel option 
> which can do the magic? If not, and kernel can allocated hugepages in 
> non-contiguous memory how dpdk is going to resolve it?
>

I don't think there is anything we can do to force the kernel to 
pre-allocate contig hugepages on boot. If there was, we wouldn't need to 
do all this mapping sorting and grouping we do on DPDK
as we would rely on the kernel giving us pre-allocated contig hugepages.

If you have plenty of memory one possible work around would be to 
increase the number of default hugepages so we are likely to find more 
contiguous ones.

Is using 1GB hugepages a possibility in your case?

Sergio

> Thanks in advance,
> Renata
>