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From:   David Wysochanski <dwysocha@redhat.com>
Date:   Tue, 4 Jan 2022 06:27:20 -0500
Message-ID: <CALF+zOnfUf4=c+digFzNjgjJN6wdxwusUvMN1=0YeTommx8fBg@mail.gmail.com>
Subject: Re: [PATCH v4 00/68] fscache, cachefiles: Rewrite
To:     David Howells <dhowells@redhat.com>
Cc:     linux-cachefs <linux-cachefs@redhat.com>,
        Jeff Layton <jlayton@kernel.org>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        linux-nfs <linux-nfs@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, Dec 22, 2021 at 6:13 PM David Howells <dhowells@redhat.com> wrote:
>
>
> Here's a set of patches implements a rewrite of the fscache driver and a
> matching rewrite of the cachefiles driver, significantly simplifying the
> code compared to what's upstream, removing the complex operation scheduling
> and object state machine in favour of something much smaller and simpler.
>
> The patchset is structured such that the first few patches disable fscache
> use by the network filesystems using it, remove the cachefiles driver
> entirely and as much of the fscache driver as can be got away with without
> causing build failures in the network filesystems.  The patches after that
> recreate fscache and then cachefiles, attempting to add the pieces in a
> logical order.  Finally, the filesystems are reenabled and then the very
> last patch changes the documentation.
>
>
> WHY REWRITE?
> ============
>
> Fscache's operation scheduling API was intended to handle sequencing of
> cache operations, which were all required (where possible) to run
> asynchronously in parallel with the operations being done by the network
> filesystem, whilst allowing the cache to be brought online and offline and
> to interrupt service for invalidation.
>
> With the advent of the tmpfile capacity in the VFS, however, an opportunity
> arises to do invalidation much more simply, without having to wait for I/O
> that's actually in progress: Cachefiles can simply create a tmpfile, cut
> over the file pointer for the backing object attached to a cookie and
> abandon the in-progress I/O, dismissing it upon completion.
>
> Future work here would involve using Omar Sandoval's vfs_link() with
> AT_LINK_REPLACE[1] to allow an extant file to be displaced by a new hard
> link from a tmpfile as currently I have to unlink the old file first.
>
> These patches can also simplify the object state handling as I/O operations
> to the cache don't all have to be brought to a stop in order to invalidate
> a file.  To that end, and with an eye on to writing a new backing cache
> model in the future, I've taken the opportunity to simplify the indexing
> structure.
>
> I've separated the index cookie concept from the file cookie concept by C
> type now.  The former is now called a "volume cookie" (struct
> fscache_volume) and there is a container of file cookies.  There are then
> just the two levels.  All the index cookie levels are collapsed into a
> single volume cookie, and this has a single printable string as a key.  For
> instance, an AFS volume would have a key of something like
> "afs,example.com,1000555", combining the filesystem name, cell name and
> volume ID.  This is freeform, but must not have '/' chars in it.
>
> I've also eliminated all pointers back from fscache into the network
> filesystem.  This required the duplication of a little bit of data in the
> cookie (cookie key, coherency data and file size), but it's not actually
> that much.  This gets rid of problems with making sure we keep netfs data
> structures around so that the cache can access them.
>
> These patches mean that most of the code that was in the drivers before is
> simply gone and those drivers are now almost entirely new code.  That being
> the case, there doesn't seem any particular reason to try and maintain
> bisectability across it.  Further, there has to be a point in the middle
> where things are cut over as there's a single point everything has to go
> through (ie. /dev/cachefiles) and it can't be in use by two drivers at
> once.
>
>
> ISSUES YET OUTSTANDING
> ======================
>
> There are some issues still outstanding, unaddressed by this patchset, that
> will need fixing in future patchsets, but that don't stop this series from
> being usable:
>
>  (1) The cachefiles driver needs to stop using the backing filesystem's
>      metadata to store information about what parts of the cache are
>      populated.  This is not reliable with modern extent-based filesystems.
>
>      Fixing this is deferred to a separate patchset as it involves
>      negotiation with the network filesystem and the VM as to how much data
>      to download to fulfil a read - which brings me on to (2)...
>
>  (2) NFS and CIFS do not take account of how the cache would like I/O to be
>      structured to meet its granularity requirements.  Previously, the
>      cache used page granularity, which was fine as the network filesystems
>      also dealt in page granularity, and the backing filesystem (ext4, xfs
>      or whatever) did whatever it did out of sight.  However, we now have
>      folios to deal with and the cache will now have to store its own
>      metadata to track its contents.
>
>      The change I'm looking at making for cachefiles is to store content
>      bitmaps in one or more xattrs and making a bit in the map correspond
>      to something like a 256KiB block.  However, the size of an xattr and
>      the fact that they have to be read/updated in one go means that I'm
>      looking at covering 1GiB of data per 512-byte map and storing each map
>      in an xattr.  Cachefiles has the potential to grow into a fully
>      fledged filesystem of its very own if I'm not careful.
>
>      However, I'm also looking at changing things even more radically and
>      going to a different model of how the cache is arranged and managed -
>      one that's more akin to the way, say, openafs does things - which
>      brings me on to (3)...
>
>  (3) The way cachefilesd does culling is very inefficient for large caches
>      and it would be better to move it into the kernel if I can as
>      cachefilesd has to keep asking the kernel if it can cull a file.
>      Changing the way the backend works would allow this to be addressed.
>
>
> BITS THAT MAY BE CONTROVERSIAL
> ==============================
>
> There are some bits I've added that may be controversial:
>
>  (1) I've provided a flag, S_KERNEL_FILE, that cachefiles uses to check if
>      a files is already being used by some other kernel service (e.g. a
>      duplicate cachefiles cache in the same directory) and reject it if it
>      is.  This isn't entirely necessary, but it helps prevent accidental
>      data corruption.
>
>      I don't want to use S_SWAPFILE as that has other effects, but quite
>      possibly swapon() should set S_KERNEL_FILE too.
>
>      Note that it doesn't prevent userspace from interfering, though
>      perhaps it should.  (I have made it prevent a marked directory from
>      being rmdir-able).
>
>  (2) Cachefiles wants to keep the backing file for a cookie open whilst we
>      might need to write to it from network filesystem writeback.  The
>      problem is that the network filesystem unuses its cookie when its file
>      is closed, and so we have nothing pinning the cachefiles file open and
>      it will get closed automatically after a short time to avoid
>      EMFILE/ENFILE problems.
>
>      Reopening the cache file, however, is a problem if this is being done
>      due to writeback triggered by exit().  Some filesystems will oops if
>      we try to open a file in that context because they want to access
>      current->fs or suchlike.
>
>      To get around this, I added the following:
>
>      (A) An inode flag, I_PINNING_FSCACHE_WB, to be set on a network
>          filesystem inode to indicate that we have a usage count on the
>          cookie caching that inode.
>
>      (B) A flag in struct writeback_control, unpinned_fscache_wb, that is
>          set when __writeback_single_inode() clears the last dirty page
>          from i_pages - at which point it clears I_PINNING_FSCACHE_WB and
>          sets this flag.
>
>          This has to be done here so that clearing I_PINNING_FSCACHE_WB can
>          be done atomically with the check of PAGECACHE_TAG_DIRTY that
>          clears I_DIRTY_PAGES.
>
>      (C) A function, fscache_set_page_dirty(), which if it is not set, sets
>          I_PINNING_FSCACHE_WB and calls fscache_use_cookie() to pin the
>          cache resources.
>
>      (D) A function, fscache_unpin_writeback(), to be called by
>          ->write_inode() to unuse the cookie.
>
>      (E) A function, fscache_clear_inode_writeback(), to be called when the
>          inode is evicted, before clear_inode() is called.  This cleans up
>          any lingering I_PINNING_FSCACHE_WB.
>
>      The network filesystem can then use these tools to make sure that
>      fscache_write_to_cache() can write locally modified data to the cache
>      as well as to the server.
>
>      For the future, I'm working on write helpers for netfs lib that should
>      allow this facility to be removed by keeping track of the dirty
>      regions separately - but that's incomplete at the moment and is also
>      going to be affected by folios, one way or another, since it deals
>      with pages.
>
>
> These patches can be found also on:
>
>         https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=fscache-rewrite
>
> David
>
>
> Changes
> =======
> ver #4:
>  - Dropped a pair of patches to try and cope with multipage folios in
>    afs_write_begin/end() - it should really be done in the caller[7].
>  - Fixed the use of sizeof with memset in cifs.
>  - Removed an extraneous kdoc param.
>  - Added a patch to add a tracepoint for fscache_use/unuse_cookie().
>  - In cifs, tcon->vol_create_time is __le64 so doesn't need cpu_to_le64().
>  - Add an expanded version of a patch to use current_is_kswapd() instead of
>    !gfpflags_allow_blocking()[8].
>  - Removed a couple of debugging print statements.
>
> ver #3:
>  - Fixed a race in the cookie state machine between LRU discard and
>    relinquishment[4].
>  - Fixed up the hashing to make it portable[5].
>  - Fixed up some netfs coherency data to make it portable.
>  - Fixed some missing NFS_FSCACHE=n fallback functions in nfs[6].
>  - Added a patch to store volume coherency data in an xattr.
>  - Added a check that the cookie is unhashed before being freed.
>  - Fixed fscache to use remove_proc_subtree() to remove /proc/fs/fscache/.
>
> ver #2:
>  - Fix an unused-var warning due to CONFIG_9P_FSCACHE=n.
>  - Use gfpflags_allow_blocking() rather than using flag directly.
>  - Fixed some error logging in a couple of cachefiles functions.
>  - Fixed an error check in the fscache volume allocation.
>  - Need to unmark an inode we've moved to the graveyard before unlocking.
>  - Upgraded to -rc4 to allow for upstream changes to cifs.
>  - Should only change to inval state if can get access to cache.
>  - Don't hold n_accesses elevated whilst cache is bound to a cookie, but
>    rather add a flag that prevents the state machine from being queued when
>    n_accesses reaches 0.
>  - Remove the unused cookie pointer field from the fscache_acquire
>    tracepoint.
>  - Added missing transition to LRU_DISCARDING state.
>  - Added two ceph patches from Jeff Layton[2].
>  - Remove NFS_INO_FSCACHE as it's no longer used.
>  - In NFS, need to unuse a cookie on file-release, not inode-clear.
>  - Filled in the NFS cache I/O routines, borrowing from the previously posted
>    fallback I/O code[3].
>
>
> Link: https://lore.kernel.org/r/cover.1580251857.git.osandov@fb.com/ [1]
> Link: https://lore.kernel.org/r/20211207134451.66296-1-jlayton@kernel.org/ [2]
> Link: https://lore.kernel.org/r/163189108292.2509237.12615909591150927232.stgit@warthog.procyon.org.uk/ [3]
> Link: https://lore.kernel.org/r/599331.1639410068@warthog.procyon.org.uk/ [4]
> Link: https://lore.kernel.org/r/CAHk-=whtkzB446+hX0zdLsdcUJsJ=8_-0S1mE_R+YurThfUbLA@mail.gmail.com [5]
> Link: https://lore.kernel.org/r/61b90f3d.H1IkoeQfEsGNhvq9%lkp@intel.com/ [6]
> Link: https://lore.kernel.org/r/CAHk-=wh2dr=NgVSVj0sw-gSuzhxhLRV5FymfPS146zGgF4kBjA@mail.gmail.com/ [7]
> Link: https://lore.kernel.org/r/1638952658-20285-1-git-send-email-huangzhaoyang@gmail.com/ [8]
>
>
> References
> ==========
>
> These patches have been published for review before, firstly as part of a
> larger set:
>
> Link: https://lore.kernel.org/r/158861203563.340223.7585359869938129395.stgit@warthog.procyon.org.uk/
>
> Link: https://lore.kernel.org/r/159465766378.1376105.11619976251039287525.stgit@warthog.procyon.org.uk/
> Link: https://lore.kernel.org/r/159465784033.1376674.18106463693989811037.stgit@warthog.procyon.org.uk/
> Link: https://lore.kernel.org/r/159465821598.1377938.2046362270225008168.stgit@warthog.procyon.org.uk/
>
> Link: https://lore.kernel.org/r/160588455242.3465195.3214733858273019178.stgit@warthog.procyon.org.uk/
>
> Then as a cut-down set:
>
> Link: https://lore.kernel.org/r/161118128472.1232039.11746799833066425131.stgit@warthog.procyon.org.uk/ # v1
> Link: https://lore.kernel.org/r/161161025063.2537118.2009249444682241405.stgit@warthog.procyon.org.uk/ # v2
> Link: https://lore.kernel.org/r/161340385320.1303470.2392622971006879777.stgit@warthog.procyon.org.uk/ # v3
> Link: https://lore.kernel.org/r/161539526152.286939.8589700175877370401.stgit@warthog.procyon.org.uk/ # v4
> Link: https://lore.kernel.org/r/161653784755.2770958.11820491619308713741.stgit@warthog.procyon.org.uk/ # v5
>
> I split out a set to just restructure the I/O, which got merged back in to
> this one:
>
> Link: https://lore.kernel.org/r/163363935000.1980952.15279841414072653108.stgit@warthog.procyon.org.uk/
> Link: https://lore.kernel.org/r/163189104510.2509237.10805032055807259087.stgit@warthog.procyon.org.uk/ # v2
> Link: https://lore.kernel.org/r/163363935000.1980952.15279841414072653108.stgit@warthog.procyon.org.uk/ # v3
> Link: https://lore.kernel.org/r/163551653404.1877519.12363794970541005441.stgit@warthog.procyon.org.uk/ # v4
>
> ... and a larger set to do the conversion, also merged back into this one:
>
> Link: https://lore.kernel.org/r/163456861570.2614702.14754548462706508617.stgit@warthog.procyon.org.uk/ # v1
> Link: https://lore.kernel.org/r/163492911924.1038219.13107463173777870713.stgit@warthog.procyon.org.uk/ # v2
>
> Older versions of this one:
>
> Link: https://lore.kernel.org/r/163819575444.215744.318477214576928110.stgit@warthog.procyon.org.uk/ # v1
> Link: https://lore.kernel.org/r/163906878733.143852.5604115678965006622.stgit@warthog.procyon.org.uk/ # v2
> Link: https://lore.kernel.org/r/163967073889.1823006.12237147297060239168.stgit@warthog.procyon.org.uk/ # v3
>
> Proposals/information about the design have been published here:
>
> Link: https://lore.kernel.org/r/24942.1573667720@warthog.procyon.org.uk/
> Link: https://lore.kernel.org/r/2758811.1610621106@warthog.procyon.org.uk/
> Link: https://lore.kernel.org/r/1441311.1598547738@warthog.procyon.org.uk/
> Link: https://lore.kernel.org/r/160655.1611012999@warthog.procyon.org.uk/
>
> And requests for information:
>
> Link: https://lore.kernel.org/r/3326.1579019665@warthog.procyon.org.uk/
> Link: https://lore.kernel.org/r/4467.1579020509@warthog.procyon.org.uk/
> Link: https://lore.kernel.org/r/3577430.1579705075@warthog.procyon.org.uk/
>
> I've posted partial patches to try and help 9p and cifs along:
>
> Link: https://lore.kernel.org/r/1514086.1605697347@warthog.procyon.org.uk/
> Link: https://lore.kernel.org/r/1794123.1605713481@warthog.procyon.org.uk/
> Link: https://lore.kernel.org/r/241017.1612263863@warthog.procyon.org.uk/
> Link: https://lore.kernel.org/r/270998.1612265397@warthog.procyon.org.uk/
>
> ---
> Dave Wysochanski (1):
>       nfs: Convert to new fscache volume/cookie API
>
> David Howells (65):
>       fscache, cachefiles: Disable configuration
>       cachefiles: Delete the cachefiles driver pending rewrite
>       fscache: Remove the contents of the fscache driver, pending rewrite
>       netfs: Display the netfs inode number in the netfs_read tracepoint
>       netfs: Pass a flag to ->prepare_write() to say if there's no alloc'd space
>       fscache: Introduce new driver
>       fscache: Implement a hash function
>       fscache: Implement cache registration
>       fscache: Implement volume registration
>       fscache: Implement cookie registration
>       fscache: Implement cache-level access helpers
>       fscache: Implement volume-level access helpers
>       fscache: Implement cookie-level access helpers
>       fscache: Implement functions add/remove a cache
>       fscache: Provide and use cache methods to lookup/create/free a volume
>       fscache: Add a function for a cache backend to note an I/O error
>       fscache: Implement simple cookie state machine
>       fscache: Implement cookie user counting and resource pinning
>       fscache: Implement cookie invalidation
>       fscache: Provide a means to begin an operation
>       fscache: Count data storage objects in a cache
>       fscache: Provide read/write stat counters for the cache
>       fscache: Provide a function to let the netfs update its coherency data
>       netfs: Pass more information on how to deal with a hole in the cache
>       fscache: Implement raw I/O interface
>       fscache: Implement higher-level write I/O interface
>       vfs, fscache: Implement pinning of cache usage for writeback
>       fscache: Provide a function to note the release of a page
>       fscache: Provide a function to resize a cookie
>       cachefiles: Introduce rewritten driver
>       cachefiles: Define structs
>       cachefiles: Add some error injection support
>       cachefiles: Add a couple of tracepoints for logging errors
>       cachefiles: Add cache error reporting macro
>       cachefiles: Add security derivation
>       cachefiles: Register a miscdev and parse commands over it
>       cachefiles: Provide a function to check how much space there is
>       vfs, cachefiles: Mark a backing file in use with an inode flag
>       cachefiles: Implement a function to get/create a directory in the cache
>       cachefiles: Implement cache registration and withdrawal
>       cachefiles: Implement volume support
>       cachefiles: Add tracepoints for calls to the VFS
>       cachefiles: Implement object lifecycle funcs
>       cachefiles: Implement key to filename encoding
>       cachefiles: Implement metadata/coherency data storage in xattrs
>       cachefiles: Mark a backing file in use with an inode flag
>       cachefiles: Implement culling daemon commands
>       cachefiles: Implement backing file wrangling
>       cachefiles: Implement begin and end I/O operation
>       cachefiles: Implement cookie resize for truncate
>       cachefiles: Implement the I/O routines
>       fscache, cachefiles: Store the volume coherency data
>       cachefiles: Allow cachefiles to actually function
>       fscache, cachefiles: Display stats of no-space events
>       fscache, cachefiles: Display stat of culling events
>       afs: Convert afs to use the new fscache API
>       afs: Copy local writes to the cache when writing to the server
>       afs: Skip truncation on the server of data we haven't written yet
>       9p: Use fscache indexing rewrite and reenable caching
>       9p: Copy local writes to the cache when writing to the server
>       nfs: Implement cache I/O by accessing the cache directly
>       cifs: Support fscache indexing rewrite (untested)
>       fscache: Rewrite documentation
>       fscache: Add a tracepoint for cookie use/unuse
>       9p, afs, ceph, cifs, nfs: Use current_is_kswapd() rather than gfpflags_allow_blocking()
>
> Jeff Layton (2):
>       ceph: conversion to new fscache API
>       ceph: add fscache writeback support
>
>
>  .../filesystems/caching/backend-api.rst       |  850 ++++------
>  .../filesystems/caching/cachefiles.rst        |    6 +-
>  Documentation/filesystems/caching/fscache.rst |  525 ++----
>  Documentation/filesystems/caching/index.rst   |    4 +-
>  .../filesystems/caching/netfs-api.rst         | 1136 ++++---------
>  Documentation/filesystems/caching/object.rst  |  313 ----
>  .../filesystems/caching/operations.rst        |  210 ---
>  Documentation/filesystems/netfs_library.rst   |   16 +-
>  fs/9p/Kconfig                                 |    2 +-
>  fs/9p/cache.c                                 |  195 +--
>  fs/9p/cache.h                                 |   25 +-
>  fs/9p/v9fs.c                                  |   17 +-
>  fs/9p/v9fs.h                                  |   13 +-
>  fs/9p/vfs_addr.c                              |   57 +-
>  fs/9p/vfs_dir.c                               |   13 +
>  fs/9p/vfs_file.c                              |    3 +-
>  fs/9p/vfs_inode.c                             |   26 +-
>  fs/9p/vfs_inode_dotl.c                        |    3 +-
>  fs/9p/vfs_super.c                             |    3 +
>  fs/afs/Kconfig                                |    2 +-
>  fs/afs/Makefile                               |    3 -
>  fs/afs/cache.c                                |   68 -
>  fs/afs/cell.c                                 |   12 -
>  fs/afs/file.c                                 |   38 +-
>  fs/afs/inode.c                                |  101 +-
>  fs/afs/internal.h                             |   37 +-
>  fs/afs/main.c                                 |   14 -
>  fs/afs/super.c                                |    1 +
>  fs/afs/volume.c                               |   29 +-
>  fs/afs/write.c                                |   88 +-
>  fs/cachefiles/Kconfig                         |    7 +
>  fs/cachefiles/Makefile                        |    6 +-
>  fs/cachefiles/bind.c                          |  278 ----
>  fs/cachefiles/cache.c                         |  378 +++++
>  fs/cachefiles/daemon.c                        |  180 +-
>  fs/cachefiles/error_inject.c                  |   46 +
>  fs/cachefiles/interface.c                     |  747 ++++-----
>  fs/cachefiles/internal.h                      |  270 +--
>  fs/cachefiles/io.c                            |  330 +++-
>  fs/cachefiles/key.c                           |  201 ++-
>  fs/cachefiles/main.c                          |   22 +-
>  fs/cachefiles/namei.c                         | 1223 ++++++--------
>  fs/cachefiles/rdwr.c                          |  972 -----------
>  fs/cachefiles/security.c                      |    2 +-
>  fs/cachefiles/volume.c                        |  139 ++
>  fs/cachefiles/xattr.c                         |  421 ++---
>  fs/ceph/Kconfig                               |    2 +-
>  fs/ceph/addr.c                                |  102 +-
>  fs/ceph/cache.c                               |  218 +--
>  fs/ceph/cache.h                               |   97 +-
>  fs/ceph/caps.c                                |    3 +-
>  fs/ceph/file.c                                |   13 +-
>  fs/ceph/inode.c                               |   22 +-
>  fs/ceph/super.c                               |   10 +-
>  fs/ceph/super.h                               |    3 +-
>  fs/cifs/Kconfig                               |    2 +-
>  fs/cifs/Makefile                              |    2 +-
>  fs/cifs/cache.c                               |  105 --
>  fs/cifs/cifsfs.c                              |   11 +-
>  fs/cifs/cifsglob.h                            |    5 +-
>  fs/cifs/connect.c                             |   12 -
>  fs/cifs/file.c                                |   64 +-
>  fs/cifs/fscache.c                             |  333 +---
>  fs/cifs/fscache.h                             |  126 +-
>  fs/cifs/inode.c                               |   36 +-
>  fs/fs-writeback.c                             |    8 +
>  fs/fscache/Makefile                           |    6 +-
>  fs/fscache/cache.c                            |  618 +++----
>  fs/fscache/cookie.c                           | 1448 +++++++++--------
>  fs/fscache/fsdef.c                            |   98 --
>  fs/fscache/internal.h                         |  317 +---
>  fs/fscache/io.c                               |  376 ++++-
>  fs/fscache/main.c                             |  147 +-
>  fs/fscache/netfs.c                            |   74 -
>  fs/fscache/object.c                           | 1125 -------------
>  fs/fscache/operation.c                        |  633 -------
>  fs/fscache/page.c                             | 1242 --------------
>  fs/fscache/proc.c                             |   47 +-
>  fs/fscache/stats.c                            |  293 +---
>  fs/fscache/volume.c                           |  517 ++++++
>  fs/namei.c                                    |    3 +-
>  fs/netfs/read_helper.c                        |   10 +-
>  fs/nfs/Kconfig                                |    2 +-
>  fs/nfs/Makefile                               |    2 +-
>  fs/nfs/client.c                               |    4 -
>  fs/nfs/direct.c                               |    2 +
>  fs/nfs/file.c                                 |   13 +-
>  fs/nfs/fscache-index.c                        |  140 --
>  fs/nfs/fscache.c                              |  490 ++----
>  fs/nfs/fscache.h                              |  180 +-
>  fs/nfs/inode.c                                |   11 +-
>  fs/nfs/nfstrace.h                             |    1 -
>  fs/nfs/read.c                                 |   25 +-
>  fs/nfs/super.c                                |   28 +-
>  fs/nfs/write.c                                |    8 +-
>  include/linux/fs.h                            |    4 +
>  include/linux/fscache-cache.h                 |  614 ++-----
>  include/linux/fscache.h                       | 1021 +++++-------
>  include/linux/netfs.h                         |   15 +-
>  include/linux/nfs_fs.h                        |    1 -
>  include/linux/nfs_fs_sb.h                     |    9 +-
>  include/linux/writeback.h                     |    1 +
>  include/trace/events/cachefiles.h             |  527 ++++--
>  include/trace/events/fscache.h                |  642 ++++----
>  include/trace/events/netfs.h                  |    5 +-
>  105 files changed, 7396 insertions(+), 13509 deletions(-)
>  delete mode 100644 Documentation/filesystems/caching/object.rst
>  delete mode 100644 Documentation/filesystems/caching/operations.rst
>  delete mode 100644 fs/afs/cache.c
>  delete mode 100644 fs/cachefiles/bind.c
>  create mode 100644 fs/cachefiles/cache.c
>  create mode 100644 fs/cachefiles/error_inject.c
>  delete mode 100644 fs/cachefiles/rdwr.c
>  create mode 100644 fs/cachefiles/volume.c
>  delete mode 100644 fs/cifs/cache.c
>  delete mode 100644 fs/fscache/fsdef.c
>  delete mode 100644 fs/fscache/netfs.c
>  delete mode 100644 fs/fscache/object.c
>  delete mode 100644 fs/fscache/operation.c
>  delete mode 100644 fs/fscache/page.c
>  create mode 100644 fs/fscache/volume.c
>  delete mode 100644 fs/nfs/fscache-index.c
>
>

Tested this with NFS and fscache enabled and disabled looks very
stable.  You can add
Tested-by: Dave Wysochanski <dwysocha@redhat.com>

Since this set was on top of 5.16.0-rc4, I compared runs of vanilla
5.16.0-rc4 and this set.
No new failures were seen, no oops or warns, or other stability
issues, and many runs I ran back to back without reboots.

Summary of tests
- NFS fscache unit tests: PASS
- xfstests vers=4.2,fsc,nofsc (Hammerspace pNFS flexfiles, RHEL 8u4): PASS
- xfstests vers=4.1,fsc,nofsc (Hammerspace pNFS flexfiles, NetApp
Ontap 9.x pNFS files): PASS
- xfstests vers=4.0,fsc,nofsc (NetApp Ontap 9.x pNFS files, RHEL 8u4): PASS
- xfstests vers=3 (RHEL 8u4): PASS