[RFC PATCH 0/3] Convert NFS to the new netfs API

[Dave Wysochanski <dwysocha@redhat.com>]

This patchset converts NFS non-direct READ IO paths to unconditionally
use the netfs API with a non-invasive approach.  The existing NFS pgio
layer does not need extensive changes, and is the best way so far I've
found to avoid Trond's earlier objection [1].  I have not yet attempted
performance comparisions to address Chuck Lever's concern [2].

The main patch to be reviewed is patch #3 which converts nfs_read_folio
and nfs_readahead.

I do not really like this patchset but so far this is what I was able
to come up with the move things forward.  I think it is awkward and
still needs work, has some issues (below) though it is fairly stable
by running xfstests generic with various servers.  The known issues
are as follows:

1. Unit test setting rsize < readahead does not properly read from
fscache but re-reads data from the NFS server
* This will be fixed once another linux-cachefs [3] patch to resolve
"Stop read optimisation when folio removed from pagecache"

2. "Cache volume key already in use" after xfstest runs
* xfstests (hammerspace with vers=4.2,fsc) shows the following on the
console after some tests:
"NFS: Cache volume key already in use (nfs,4.1,2,c50,cfe0100a,3,,,8000,100000,100000,bb8,ea60,7530,ea60,1)"
* This may be fixed with another patch [4] that is in progress

3. Occasional process IO hangs in read paths
* May be due to out-of-order RPC replies or something unique to NetApp
triggering a bug in the conversion patch
* xfstests (Example: generic/075 with netapp ontap9 vers=4.1)
* Sample backtrace
 #2 [ffff888104967990] io_schedule at ffffffffbc46969d
 #3 [ffff8881049679b0] folio_wait_bit_common at ffffffffbb40214b
 #4 [ffff888104967ad0] filemap_get_pages at ffffffffbb40688c
 #5 [ffff888104967c00] filemap_read at ffffffffbb406a61
 #6 [ffff888104967d80] nfs_file_read at ffffffffc0e0f415 [nfs]
 #7 [ffff888104967db0] vfs_read at ffffffffbb5681a5

4. Data corruption seen with unit test where rsize < readahead
* Seen with vanilla 6.0-rc2 (did not occur on 5.19); likely unrelated
to this patchset
 mount -o vers=4.2,fsc,rsize=8192 127.0.0.1:/export /mnt
 dd if=/dev/urandom of=/tmp/integrity-rsize-file1.bin bs=16k count=1
 ./nfs-readahead.sh set /mnt 16384
 dd if=/tmp/integrity-rsize-file1.bin of=/mnt/integrity-rsize-file1.bin bs=16k count=1
 echo 3 > /proc/sys/vm/drop_caches
 md5sum /mnt/integrity-rsize-file1.bin /tmp/integrity-rsize-file1.bin
 md5sums don't match, MD5_NFS = 00eaf1a5bc1b3dfd54711db551619afa != MD5_LOCAL = e8d835c83ba1f1264869dc40673fa20c


The patchset is based on 6.0-rc2 and has been pushed to github at:
https://github.com/DaveWysochanskiRH/kernel/commits/nfs-fscache-netfs

[1] https://lore.kernel.org/linux-nfs/9cfd5bc3cfc6abc2d3316b0387222e708d67f595.camel@hammerspace.com/
[2] https://marc.info/?l=linux-nfs&m=160597917525083&w=4
[3] https://www.mail-archive.com/linux-cachefs@redhat.com/msg03043.html
[4] https://marc.info/?l=linux-nfs&m=165962662200679&w=4

Dave Wysochanski (3):
  NFS: Rename readpage_async_filler to nfs_pageio_add_page
  NFS: Add support for netfs in struct nfs_inode and Kconfig
  NFS: Convert nfs_read_folio and nfs_readahead to netfs APIs

 fs/nfs/Kconfig           |   1 +
 fs/nfs/delegation.c      |   2 +-
 fs/nfs/dir.c             |   2 +-
 fs/nfs/fscache.c         | 191 ++++++++++++++++++---------------------
 fs/nfs/fscache.h         |  77 ++++++++--------
 fs/nfs/inode.c           |   8 +-
 fs/nfs/internal.h        |  10 +-
 fs/nfs/pagelist.c        |  14 +++
 fs/nfs/pnfs.c            |  12 +--
 fs/nfs/read.c            | 117 ++++++++----------------
 fs/nfs/write.c           |   2 +-
 include/linux/nfs_fs.h   |  19 +---
 include/linux/nfs_page.h |   1 +
 include/linux/nfs_xdr.h  |   1 +
 14 files changed, 210 insertions(+), 247 deletions(-)

-- 
2.31.1