Re: [RFC PATCH 0/7] block, fs: convert Direct IO to FOLL_PIN

[John Hubbard <jhubbard@nvidia.com>]

On 2/25/22 04:05, Jan Kara wrote:
...
>> After quite some time exploring and consulting with people as well, it
>> is clear that this cannot be done in just one patchset. That's because,
>> not only is this large and time-consuming (for example, Chaitanya
>> Kulkarni's first reaction, after looking into the details, was, "convert
>> the remaining filesystems to use iomap, *then* convert to FOLL_PIN..."),
>> but it is also spread across many filesystems.
> 
> With having modified fs/direct-io.c and fs/iomap/direct-io.c which
> filesystems do you know are missing conversion? Or is it that you just want
> to make sure with audit everything is fine? The only fs I could find
> unconverted by your changes is ceph. Am I missing something?
> 
> 								Honza

There are a few more filesystems that call iov_iter_get_pages() or
iov_iter_get_pages_alloc(), plus networking things as well, plus some
others that are hard to categorize, such as vhost. So we have:

* ceph
* rds
* cifs
* p9
* net: __zerocopy_sg_from_iter(), tls_setup_from_iter(),
* crypto: af_alg_make_sg() (maybe N/A)
* vmsplice() (as David Hildenbrand mentioned)
* vhost: vhost_scsi_map_to_sgl()

In addition to that, I was also worried that maybe the
blockdev_direct_IO() or iomap filesystems might be breaking encapsulation
occasionally, by calling put_page() on the direct IO user page buffer.
Perhaps in error paths.

Are you pretty sure that that last concern is not valid? That would be a
welcome bit of news.



thanks,
-- 
John Hubbard
NVIDIA