Thread (31 messages) 31 messages, 5 authors, 2022-09-01

Re: [PATCH 5/6] NFS: direct-io: convert to FOLL_PIN pages

From: John Hubbard <jhubbard@nvidia.com>
Date: 2022-08-28 00:46:35
Also in: linux-fsdevel, linux-mm, linux-nfs, linux-xfs, lkml

On 8/27/22 17:39, Al Viro wrote:
On Sun, Aug 28, 2022 at 01:38:57AM +0100, Al Viro wrote:
quoted
On Sat, Aug 27, 2022 at 04:55:18PM -0700, John Hubbard wrote:
quoted
On 8/27/22 15:48, Al Viro wrote:
quoted
On Sat, Aug 27, 2022 at 01:36:06AM -0700, John Hubbard wrote:
quoted
Convert the NFS Direct IO layer to use pin_user_pages_fast() and
unpin_user_page(), instead of get_user_pages_fast() and put_page().
Again, this stuff can be hit with ITER_BVEC iterators
quoted
-		result = iov_iter_get_pages_alloc2(iter, &pagevec,
+		result = dio_w_iov_iter_pin_pages_alloc(iter, &pagevec,
 						  rsize, &pgbase);
and this will break on those.
If anyone has an example handy, of a user space program that leads
to this situation (O_DIRECT with ITER_BVEC), it would really help
me reach enlightenment a lot quicker in this area. :)
Er...  splice(2) to O_DIRECT-opened file on e.g. ext4?  Or
sendfile(2) to the same, for that matter...
s/ext4/nfs/ to hit this particular codepath, obviously.
aha, thanks. I do remember that you alerted me earlier to splice(2)
problems, and I thought I'd neatly sidestepped those this time, by
staying with user_backed_iter(i) cases. 

But I see that it's going to take something more, after all.



thanks,

-- 
John Hubbard
NVIDIA
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