Re: [RFC PATCH v2 00/19] RDMA/FS DAX truncate proposal V1,000,002 ;-)

John Hubbard
2019-08-21T18:45:34Z

On 8/19/19 8:36 PM, Dave Chinner wrote:
> On Mon, Aug 19, 2019 at 08:09:33PM -0700, John Hubbard wrote:
>> On 8/19/19 6:20 PM, Dave Chinner wrote:
>>> On Mon, Aug 19, 2019 at 05:05:53PM -0700, John Hubbard wrote:
>>>> On 8/19/19 2:24 AM, Dave Chinner wrote:
>>>>> On Mon, Aug 19, 2019 at 08:34:12AM +0200, Jan Kara wrote:
>>>>>> On Sat 17-08-19 12:26:03, Dave Chinner wrote:
>>>>>>> On Fri, Aug 16, 2019 at 12:05:28PM -0700, Ira Weiny wrote:
>>>>>>>> On Thu, Aug 15, 2019 at 03:05:58PM +0200, Jan Kara wrote:
>>>>>>>>> On Wed 14-08-19 11:08:49, Ira Weiny wrote:
>>>>>>>>>> On Wed, Aug 14, 2019 at 12:17:14PM +0200, Jan Kara wrote:
>>>> ...
> AFAIA, there is no struct file here - the memory that has been pinned
> is just something mapped into the application's address space.
>
> It seems to me that the socket here is equivalent of the RDMA handle
> that that owns the hardware that pins the pages. Again, that RDMA
> handle is not aware of waht the mapping represents, hence need to
> hold a layout lease if it's a file mapping.
>
> SO from the filesystem persepctive, there's no difference between
> XDP or RDMA - if it's a FSDAX mapping then it is DMAing directly
> into the filesystem's backing store and that will require use of
> layout leases to perform safely.
>

OK, got it! Makes perfect sense.

thanks,
--
John Hubbard
NVIDIA