Re: [dpdk-dev] Question about DPDK hugepage fd change

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

On 27-Feb-19 6:02 PM, Edwin Leung wrote:
> Hi Anatoly,
> 
> In my test for DPDK 18.11, I notice the following:
> 
> 1. Using --legacy-mem switch, DPDK still opens 1 fd/huge page.  In essence, it is the same with or without this switch.
> 
> 2. Using --single-file-segments does reduce the open fd to 1.  However, for each huge page that is in-use, a .lock file is opened.  As a result, it still uses up a large number of fd's.
> 
> Thanks.
> --  edwin
> 
> -----Original Message-----
> From: Iain Barker
> Sent: Wednesday, February 27, 2019 8:57 AM
> To: Burakov, Anatoly <anatoly.burakov@intel.com>; Wiles, Keith <keith.wiles@intel.com>
> Cc: dev@dpdk.org; Edwin Leung <edwin.leung@oracle.com>
> Subject: RE: [dpdk-dev] Question about DPDK hugepage fd change
> 
> Original Message from: Burakov, Anatoly [mailto:anatoly.burakov@intel.com]
> 
>> I just realized that, unless you're using --legacy-mem switch, one
>> other way to alleviate the issue would be to use --single-file-segments
>> option. This will still store the fd's, however it will only do so per
>> memseg list, not per page. So, instead of 1000's of fd's with 2MB
>> pages, you'd end up with under 10. Hope this helps!
> 
> Hi Anatoly,
> 
> Thanks for the update and suggestion. We did try using --single-file-segments previously. Although it lowers the amount of fd's allocated for tracking the segments as you noted, there is still a problem.
> 
> It seems that a .lock file is created for each huge page, not for each segment. So with 2MB pages the glibc limit of 1024 fd's is still exhausted quickly if there is ~2GB of 2MB huge pages.
> 
> Edwin can provide more details from his testing. In our case much sooner, as we already use >500 fd's for the application, just 1GB of 2MB huge pages is enough to hit the fd limit due to the .lock files.
> 
> Thanks.
> 

Right, i forgot about that. Thanks for noticing! :)

By the way, i've proposed a patch for 19.05 to address this issue. The 
downside is that you'd be losing virtio with vhost-user backend support:

http://patches.dpdk.org/patch/50469/

It would be good if you tested it and reported back. Thanks!

(i should fix the wording of the documentation to avoid mentioning 
--single-file-segments as a solution - i completely forgot that it 
creates lock files...)

-- 
Thanks,
Anatoly