RE: [PATCH v2] net/af_xdp: fix umem map size for zero copy

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Ferruh Yigit [mailto:ferruh.yigit@amd.com]
> Sent: Wednesday, 22 May 2024 12.01
> 
> On 5/22/2024 2:25 AM, Du, Frank wrote:
> >> From: Ferruh Yigit <ferruh.yigit@amd.com>
> >> Sent: Wednesday, May 22, 2024 1:58 AM
> >>
> >> Isn't there a mempool flag that can help us figure out mempool is not IOVA
> >> contiguous? Isn't it sufficient on its own?
> >
> > Indeed, what we need to ascertain is whether it's contiguous in CPU virtual
> space, not IOVA. I haven't come across a flag specifically for CPU virtual
> contiguity. The major limitation in XDP is XSK UMEM only supports registering
> a single contiguous virtual memory area.
> >
> 
> 'RTE_MEMPOOL_F_NO_IOVA_CONTIG' is the flag I was looking for. This flag
> being *cleared* implies IOVA contiguous but not sure if it is
> guaranteed, need to check.

Wrong.
RTE_MEMPOOL_F_NO_IOVA_CONTIG only relates to individual objects in the pool. This flag being cleared only means that each individual object in the mempool is IOVA contiguous.
It does not imply that the entire pool of objects is IOVA contiguous.

> 
> And I may be wrong here, but as far as I remember in IOVA as VA mode,
> process virtual address and IOVA address are same, so IOVA contiguous is
> same as contiguous CPU virtual address.