linux-ext4 - Re: [RFC PATCH v2 00/19] RDMA/FS DAX truncate proposal V1,000,002 ;-)

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Date:   Wed, 21 Aug 2019 11:43:30 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Dave Chinner <david@...morbit.com>
CC:     Jan Kara <jack@...e.cz>, Ira Weiny <ira.weiny@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Theodore Ts'o" <tytso@....edu>, Michal Hocko <mhocko@...e.com>,
        <linux-xfs@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-nvdimm@...ts.01.org>, <linux-ext4@...r.kernel.org>,
        <linux-mm@...ck.org>
Subject: Re: [RFC PATCH v2 00/19] RDMA/FS DAX truncate proposal V1,000,002 ;-)

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