On 8/24/20 7:07 PM, Al Viro wrote:
On Tue, Aug 25, 2020 at 02:54:28AM +0100, Al Viro wrote:
On Fri, Aug 21, 2020 at 09:20:54PM -0700, John Hubbard wrote:
Direct IO behavior:
ITER_IOVEC:
pin_user_pages_fast();
break;
ITER_KVEC: // already elevated page refcount, leave alone
ITER_BVEC: // already elevated page refcount, leave alone
ITER_PIPE: // just, no :)
Why? What's wrong with splice to O_DIRECT file?
Sorry - s/to/from/, obviously.
To spell it out: consider generic_file_splice_read() behaviour when
the source had been opened with O_DIRECT; you will get a call of
->read_iter() into ITER_PIPE destination. And it bloody well
will hit iov_iter_get_pages() on common filesystems, to pick the
pages we want to read into.
So... what's wrong with having that "pin" primitive making sure
the pages are there and referenced by the pipe?
(our emails crossed) OK, yes, let me hook that up. I was just unaware
of that flow, I'll go off and figure it out.
Thanks for looking at this!
thanks,
--
John Hubbard
NVIDIA
