[PATCH v9 0/5] Convert NFS with fscache to the netfs API

Dave Wysochanski
2022-10-17T10:52:31Z

This patchset converts NFS with fscache non-direct READ IO paths to
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 address Trond's concerns about modifying the IO path [1] as
well as only enabling netfs when fscache is configured and enabled [2].
I have not attempted performance comparisions to address Chuck
Lever's concern [3] because we are not converting the non-fscache
enabled NFS IO paths to netfs.

No new issues found at BakeAthon testing NFSv4.2 with Hammerspace
(pNFS flexfiles) and NetApp (pNFS filelayout).

The patchset is based on 6.0 and has been pushed to github at:
https://github.com/DaveWysochanskiRH/kernel/commits/nfs-fscache-netfs
https://github.com/DaveWysochanskiRH/kernel/commit/c222ed8cd042d003ca22d890af98d9c76ec8650e

Changes since v8 [7]
====================
PATCH3-PATCH5: Add Jeff Layton Revewied-by

Testing
=======
The patches are fairly stable as evidenced with xfstests generic with
various servers, both with and without fscache enabled, with no hangs
or crashes seen:
- hammerspace(pNFS flexfiles): NFS4.1, NFS4.2
- NetApp(pNFS filelayout): NFS3, NFS4.0, NFS4.1, NFS4.2
- RHEL8: NFS3,NFS4.0,NFS4.2

Known issues
============
1. Unit test setting rsize < readahead does not properly read from
fscache but re-reads data from the NFS server
* This will be fixed with another linux-cachefs [4] patch to resolve
"Stop read optimisation when folio removed from pagecache"
* Daire Byrne also verified the patch fixes his issue as well

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 [5] that is in progress

3. Daire Byrne reported a NULL pointer oops at cachefiles_prepare_write+0x28/0x90
* harder to reproduce/debug but under investigation [6]
* only reproduced on RHEL7.9 based NFS re-export server using fscache with upstream kernel plus
the previous patches
* thought to be a bug in netfs or cachefiles exposed by NFS patches

[58710.346376] BUG: kernel NULL pointer dereference, address: 0000000000000008
[58710.371212] CPU: 12 PID: 9134 Comm: kworker/u129:0 Tainted: G E 6.0.0-2.dneg.x86_64 #1
...
[58710.389995] Workqueue: events_unbound netfs_rreq_write_to_cache_work [netfs]
[58710.397188] RIP: 0010:cachefiles_prepare_write+0x28/0x90 [cachefiles]
...
[58710.500316] Call Trace:
[58710.502894] <TASK>
[58710.505126] netfs_rreq_write_to_cache_work+0x11c/0x320 [netfs]
[58710.511201] process_one_work+0x217/0x3e0
[58710.515358] worker_thread+0x4a/0x3b0
[58710.519152] ? process_one_work+0x3e0/0x3e0
[58710.523467] kthread+0xd6/0x100
[58710.526740] ? kthread_complete_and_exit+0x20/0x20
[58710.531659] ret_from_fork+0x1f/0x30

References
==========
[1] https://lore.kernel.org/linux-nfs/9cfd5bc3cfc6abc2d3316b0387222e708d67f595.camel@hammerspace.com/
[2] https://lore.kernel.org/linux-nfs/da9200f1bded9b8b078a7aef227fd6b92eb028fb.camel@hammerspace.com/
[3] https://marc.info/?l=linux-nfs&m=160597917525083&w=4
[4] https://www.mail-archive.com/linux-cachefs@redhat.com/msg03043.html
[5] https://marc.info/?l=linux-nfs&m=165962662200679&w=4
[6] https://listman.redhat.com/archives/linux-cachefs/2022-September/007183.html
[7] https://marc.info/?l=linux-nfs&m=166385481714542&w=4

Dave Wysochanski (5):
NFS: Rename readpage_async_filler to nfs_pageio_add_page
NFS: Configure support for netfs when NFS fscache is configured
NFS: Convert buffered read paths to use netfs when fscache is enabled
NFS: Remove all NFSIOS_FSCACHE counters due to conversion to netfs API
NFS: Remove fscache specific trace points and NFS_INO_FSCACHE bit

fs/nfs/Kconfig | 1 +
fs/nfs/delegation.c | 2 +-
fs/nfs/dir.c | 2 +-
fs/nfs/fscache.c | 242 ++++++++++++++++++++++---------------
fs/nfs/fscache.h | 111 +++++++++++------
fs/nfs/inode.c | 8 +-
fs/nfs/internal.h | 11 +-
fs/nfs/iostat.h | 17 ---
fs/nfs/nfstrace.h | 91 --------------
fs/nfs/pagelist.c | 12 ++
fs/nfs/pnfs.c | 12 +-
fs/nfs/read.c | 110 +++++++++--------
fs/nfs/super.c | 11 --
fs/nfs/write.c | 2 +-
include/linux/nfs_fs.h | 35 ++++--
include/linux/nfs_iostat.h | 12 --
include/linux/nfs_page.h | 3 +
include/linux/nfs_xdr.h | 3 +
18 files changed, 335 insertions(+), 350 deletions(-)

--
2.31.1