Re: [dpdk-dev] virtio with 2MB hugepages - bringing back single file segments

["Tan, Jianfeng" <jianfeng.tan@intel.com>]

Hi Dariusz,

> -----Original Message-----
> From: Stojaczyk, DariuszX
> Sent: Friday, March 2, 2018 6:41 AM
> To: dev@dpdk.org; Tan, Jianfeng; Maxime Coquelin; Burakov, Anatoly;
> Yuanhan Liu
> Cc: Harris, James R; Thomas Monjalon
> Subject: virtio with 2MB hugepages - bringing back single file segments
> 
> Hi,
> 
> I'm trying to make a vhost-user initiator built upon DPDK work with 2MB
> hugepages. In the initiator we have to share all memory with the host
> process, so it
> can perform DMA. DPDK currently enforces having one descriptor per
> hugepage and there's an artificial limit of shared descriptors in DPDK vhost-
> user implementation (currently 8). Because of that, all DPDK vhost-user
> initiators are practically limited to 1GB hugepages at the moment. We can
> always increase the artificial descriptor limit, but then we're limited by
> sendmsg() itself, which on Linux accepts no more than 253 descriptors.
> However, could we increase the vhost-user implementation limit to - say -
> 128, and bring back "single file segments" [1]?

"Single file segments [1]" can help at the scenario that 2MB hugepages are not too scatter; i.e., some pages are physically contiguous.
But it cannot solve the issue completely (imagine the worst situation).

Plus, it makes the memory part a little complex.

So we are expecting it (with some other issues on memory part) being addressed completely by Anatoly's rework on memory.

Thanks,
Jianfeng