Re: [LSF/MM/BPF TOPIC] FOLL_PIN + file systems

["Theodore Ts'o" <tytso@mit.edu>]

On Fri, Jan 28, 2022 at 05:47:47PM -0800, John Hubbard wrote:
> By the time we meet for LSF/MM/BPF in May, the Direct IO layer will
> likely be converted to use FOLL_PIN page pinning (that is, changed from
> using get_user_pages_fast(), to pin_user_pages_fast()).
> 
> Direct IO conversion to FOLL_PIN was the last missing piece, and so the
> time is right to discuss how to use the output of all of this work
> (which is: the ability to call page_maybe_dma_pinned()), in order to fix
> one of the original problems that prompted FOLL_PIN's creation.
> 
> That problem is: file systems do not currently tolerate having their
> pages pinned and DMA'd to/from. See [1] for an extensive background of
> some 11 LWN articles since 2018.
> ....
> 
> I'll volunteer to present a few slides to provide the background and get
> the discussion started. It's critical to have filesystem people in
> attendance for this, such as Jan Kara, Dave Chinner, Christoph Hellwig,
> and many more that I won't try to list explicitly here. RDMA
> representation (Jason Gunthorpe, Leon Romanovsky, Chaitanya Kulkarni,
> and others) will help keep the file system folks from creating rules
> that break them "too much". And of course -mm folks. There are many
> people who have contributed to this project, so again, apologies for not
> listing everyone explicitly.

I'd definitely be interested in participating in this discussion,
following up on some e-mail threads that we've had on this subject.

Unfortunately a number of file system folks are listed above may not
be able to attend, so I really hope we can figure out some way to
allow remote participation for those people who aren't able to travel
due to various reasons, including corporate policies surrounding COVID.

       	       			  	    	     - Ted