Re: [Patch v3 2/6] cifs: Allocate validate negotiation request through kmalloc

[Tom Talpey]

On 4/18/2018 9:08 AM, David Laight wrote:
> From: Tom Talpey
> > Sent: 18 April 2018 12:32
> ...
> > On 4/17/2018 8:33 PM, Long Li wrote:
> > > From: Long Li <longli@xxxxxxxxxxxxx>
> > >
> > > The data buffer allocated on the stack can't be DMA'ed, and hence can't send
> > > through RDMA via SMB Direct.
> >
> > This comment is confusing. Any registered memory can be DMA'd, need to
> > state the reason for the choice here more clearly.
>
> The stack could be allocated with vmalloc().
> In which case the pages might not be physically contiguous and there is no
> (sensible) call to get the physical address required by the dma controller
> (or other bus master).

Memory registration does not requires pages to be physically contiguous.
RDMA Regions can and do support very large physical page scatter/gather,
and the adapter DMA's them readily. Is this the only reason?

Tom.