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From:   Dave Wysochanski <dwysocha@redhat.com>
To:     Trond Myklebust <trondmy@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>
Cc:     linux-nfs@vger.kernel.org, linux-cachefs@redhat.com
Subject: [RFC PATCH v1 0/13] Convert NFS client to new fscache-iter API
Date:   Wed, 15 Jul 2020 11:10:36 -0400
Message-Id: <1594825849-24991-1-git-send-email-dwysocha@redhat.com>
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk

These patches update the nfs client to use the new FS-Cache API and are at:
https://github.com/DaveWysochanskiRH/kernel/commit/a426b431873ea755c94ccd403aeaba0c4e635016

They are based on David Howells fscache-iter tree at ff12b5a05bd6984ad83e762f702cb655222bad74
https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/commit/?h=fscache-iter&id=ff12b5a05bd6984ad83e762f702cb655222bad74

The following patches may be of specific interest to review
as they are related to the conversion:
NFS: Convert fscache_acquire_cookie and fscache_relinquish_cookie
NFS: Convert nfs_readpage() and readpages() to new fscache API
NFS: Only use and unuse an fscache cookie a single time based on NFS_INO_FSCACHE
NFS: Convert fscache invalidation and update aux_data and i_size

Note that this is only a "first pass" v1 / RFC set I wanted to get
out there for the maintainers to see and know this is being worked on.
It is far from perfect and has some problems still need worked out.
A short summary of this set:

1. Takes a "least invasive to existing code" approach
* most fscache bits stay fs/nfs/fscache.[ch] 
* fscache enable/disable switched inside NFS code on nfs_inode.fscache
* only enable fscache for reads
* may not be the best approach (see future patcheset items below)

2. Basically works and passes a series of tests
* should not affect NFS when fscache is disabled (no "fsc" option)
* a couple small NFS + fscache basic verification tests
* connectathon (all NFS versions, with/without 'fsc' option)
* various iozone tests (all NFS versions, with/without 'fsc' option)

3. Still has a few known problems that are being tracked down
* Data integrity issue when write with O_DIRECT and read
back without O_DIRECT (we get 0's back from the cache)
* iozone tests run through ok but at the end superblock
cookies are left (each NFS version has a different superblock
cookie); this leads to "duplicate cookie" messages
upon subsequent mounts / runs
* A couple oopses in fscache reported to dhowells, may
be related to NFS's enable/disable of fscache on read/write
* Kernel build fails about halfway through with a strange
dubious error at the same place, linking this file:
ld: net/sunrpc/auth_gss/trace.o: attempt to load strings from a non-string section (number 41)


In addition to fixing various code issues and above issues,
a future patchset may:

1. The readpage/readpages conversion patch call read_helpers
directly rather than isolation into fs/nfs/fscache.c
* Similar to the AFS conversion, with calls directly to the
read_helpers, but not sure about non-fsc code path

2. Add write-through support
* Would probably eliminate some problematic code
paths where fscache is turned on / off depending on whether
a file switches from read to write and vice-versa
* This would rework open as well
* Have to work out whether this is possible or not and
with what caveats as far as NFS version support (is this
an NFSv4.x only thing?)

3. Rework dfprintks and/or add ftrace points
* fscache/cachefiles has 'debug' logging similar to rpcdebug
so not sure if we keep rpcdebug here or go full ftrace


Dave Wysochanski (13):
  NFS: Clean up nfs_readpage() and nfs_readpages()
  NFS: In nfs_readpage() only increment NFSIOS_READPAGES when read
    succeeds
  NFS: Refactor nfs_readpage() and nfs_readpage_async() to use
    nfs_readdesc
  NFS: Call readpage_async_filler() from nfs_readpage_async()
  NFS: Add nfs_pageio_complete_read() and remove nfs_readpage_async()
  NFS: Rename readpage_async_filler() to nfs_pageio_add_page_read()
  NFS: Convert fscache_acquire_cookie and fscache_relinquish_cookie
  NFS: Allow nfs_async_read_completion_ops to be used by other NFS code
  NFS: Convert nfs_readpage() and readpages() to new fscache API
  NFS: Allow NFS use of new fscache API in build
  NFS: Only use and unuse an fscache cookie a single time based on
    NFS_INO_FSCACHE
  NFS: Convert fscache invalidation and update aux_data and i_size
  NFS: Call nfs_fscache_invalidate() when write extends the size of the
    file

 fs/nfs/Kconfig           |   2 +-
 fs/nfs/file.c            |  20 +--
 fs/nfs/fscache-index.c   |  94 --------------
 fs/nfs/fscache.c         | 315 ++++++++++++++++++++++++-----------------------
 fs/nfs/fscache.h         |  92 +++++---------
 fs/nfs/inode.c           |   1 -
 fs/nfs/internal.h        |   4 +
 fs/nfs/pagelist.c        |   1 +
 fs/nfs/read.c            | 221 ++++++++++++++++-----------------
 fs/nfs/write.c           |   9 +-
 include/linux/nfs_fs.h   |   3 +-
 include/linux/nfs_page.h |   1 +
 include/linux/nfs_xdr.h  |   1 +
 13 files changed, 322 insertions(+), 442 deletions(-)

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1.8.3.1