Re: [PATCH v6 00/30] Network fs helper library & fscache kiocb API

[David Wysochanski <dwysocha@redhat.com>]

On Fri, Apr 9, 2021 at 8:04 AM David Wysochanski <dwysocha@redhat.com> wrote:
>
> On Thu, Apr 8, 2021 at 10:04 AM David Howells <dhowells@redhat.com> wrote:
> >
> >
> > Here's a set of patches to do two things:
> >
> >  (1) Add a helper library to handle the new VM readahead interface.  This
> >      is intended to be used unconditionally by the filesystem (whether or
> >      not caching is enabled) and provides a common framework for doing
> >      caching, transparent huge pages and, in the future, possibly fscrypt
> >      and read bandwidth maximisation.  It also allows the netfs and the
> >      cache to align, expand and slice up a read request from the VM in
> >      various ways; the netfs need only provide a function to read a stretch
> >      of data to the pagecache and the helper takes care of the rest.
> >
> >  (2) Add an alternative fscache/cachfiles I/O API that uses the kiocb
> >      facility to do async DIO to transfer data to/from the netfs's pages,
> >      rather than using readpage with wait queue snooping on one side and
> >      vfs_write() on the other.  It also uses less memory, since it doesn't
> >      do buffered I/O on the backing file.
> >
> >      Note that this uses SEEK_HOLE/SEEK_DATA to locate the data available
> >      to be read from the cache.  Whilst this is an improvement from the
> >      bmap interface, it still has a problem with regard to a modern
> >      extent-based filesystem inserting or removing bridging blocks of
> >      zeros.  Fixing that requires a much greater overhaul.
> >
> > This is a step towards overhauling the fscache API.  The change is opt-in
> > on the part of the network filesystem.  A netfs should not try to mix the
> > old and the new API because of conflicting ways of handling pages and the
> > PG_fscache page flag and because it would be mixing DIO with buffered I/O.
> > Further, the helper library can't be used with the old API.
> >
> > This does not change any of the fscache cookie handling APIs or the way
> > invalidation is done.
> >
> > In the near term, I intend to deprecate and remove the old I/O API
> > (fscache_allocate_page{,s}(), fscache_read_or_alloc_page{,s}(),
> > fscache_write_page() and fscache_uncache_page()) and eventually replace
> > most of fscache/cachefiles with something simpler and easier to follow.
> >
> > The patchset contains the following parts:
> >
> >  (1) Some helper patches, including provision of an ITER_XARRAY iov
> >      iterator and a function to do readahead expansion.
> >
> >  (2) Patches to add the netfs helper library.
> >
> >  (3) A patch to add the fscache/cachefiles kiocb API.
> >
> >  (4) Patches to add support in AFS for this.
> >
> > Jeff Layton has patches to add support in Ceph for this.
> >
> > With this, AFS without a cache passes all expected xfstests; with a cache,
> > there's an extra failure, but that's also there before these patches.
> > Fixing that probably requires a greater overhaul.  Ceph also passes the
> > expected tests.
> >
> > The netfs lib and fscache/cachefiles patches can be found also on:
> >
> >         https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=netfs-lib
> >
> > The afs patches can be found on:
> >
> >         https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=afs-netfs-lib
> >
> >
> > Changes
> > =======
> >
> > ver #6:
> >       Merged in some fixes and added an additional tracepoint[8], including
> >       fixing the amalgamation of contiguous subrequests that are to be
> >       written to the cache.
> >
> >       Added/merged some patches from Matthew Wilcox to make
> >       readahead_expand() appropriately adjust the trigger for the next
> >       readahead[9].  Also included is a patch to kerneldocify the
> >       file_ra_state struct.
> >
> >       Altered netfs_write_begin() to use DEFINE_READAHEAD()[10].
> >
> >       Split the afs patches out into their own branch.
> >
> > ver #5:
> >       Fixed some review comments from Matthew Wilcox:
> >
> >       - Put a comment into netfs_readahead() to indicate why there's a loop
> >         that puts, but doesn't unlock, "unconsumed" pages at the end when
> >         it could just return said pages to the caller to dispose of[6].
> >         (This is because where those pages are marked consumed).
> >
> >       - Use the page_file_mapping() and page_index() helper functions
> >         rather than accessing the page struct directly[6].
> >
> >       - Better names for wrangling functions for PG_private_2 and
> >         PG_fscache wrangling functions[7].  Came up with
> >         {set,end,wait_for}_page_private_2() and aliased these for fscache.
> >
> >       Moved the taking of/dropping a page ref for the PG_private_2 flag
> >       into the set and end functions.
> >
> > ver #4:
> >       Fixed some review comments from Christoph Hellwig, including dropping
> >       the export of rw_verify_area()[3] and some minor stuff[4].
> >
> >       Moved the declaration of readahead_expand() to a better location[5].
> >
> >       Rebased to v5.12-rc2 and added a bunch of references into individual
> >       commits.
> >
> >       Dropped Ceph support - that will go through the maintainer's tree.
> >
> >       Added interface documentation for the netfs helper library.
> >
> > ver #3:
> >       Rolled in the bug fixes.
> >
> >       Adjusted the functions that unlock and wait for PG_fscache according
> >       to Linus's suggestion[1].
> >
> >       Hold a ref on a page when PG_fscache is set as per Linus's
> >       suggestion[2].
> >
> >       Dropped NFS support and added Ceph support.
> >
> > ver #2:
> >       Fixed some bugs and added NFS support.
> >
> > Link: https://lore.kernel.org/r/CAHk-=wh+2gbF7XEjYc=HV9w_2uVzVf7vs60BPz0gFA=+pUm3ww@mail.gmail.com/ [1]
> > Link: https://lore.kernel.org/r/CAHk-=wjgA-74ddehziVk=XAEMTKswPu1Yw4uaro1R3ibs27ztw@mail.gmail.com/ [2]
> > Link: https://lore.kernel.org/r/20210216102614.GA27555@lst.de/ [3]
> > Link: https://lore.kernel.org/r/20210216084230.GA23669@lst.de/ [4]
> > Link: https://lore.kernel.org/r/20210217161358.GM2858050@casper.infradead.org/ [5]
> > Link: https://lore.kernel.org/r/20210321014202.GF3420@casper.infradead.org/ [6]
> > Link: https://lore.kernel.org/r/20210321105309.GG3420@casper.infradead.org/ [7]
> > Link: https://lore.kernel.org/r/161781041339.463527.18139104281901492882.stgit@warthog.procyon.org.uk/ [8]
> > Link: https://lore.kernel.org/r/20210407201857.3582797-1-willy@infradead.org/ [9]
> > Link: https://lore.kernel.org/r/1234933.1617886271@warthog.procyon.org.uk/ [10]
> >
> > 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
> >
> > Proposals/information about the design has 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/
> >
> > David
> > ---
> > David Howells (28):
> >       iov_iter: Add ITER_XARRAY
> >       mm: Add set/end/wait functions for PG_private_2
> >       mm: Implement readahead_control pageset expansion
> >       netfs: Make a netfs helper module
> >       netfs: Documentation for helper library
> >       netfs, mm: Move PG_fscache helper funcs to linux/netfs.h
> >       netfs, mm: Add set/end/wait_on_page_fscache() aliases
> >       netfs: Provide readahead and readpage netfs helpers
> >       netfs: Add tracepoints
> >       netfs: Gather stats
> >       netfs: Add write_begin helper
> >       netfs: Define an interface to talk to a cache
> >       netfs: Add a tracepoint to log failures that would be otherwise unseen
> >       fscache, cachefiles: Add alternate API to use kiocb for read/write to cache
> >       afs: Disable use of the fscache I/O routines
> >       afs: Pass page into dirty region helpers to provide THP size
> >       afs: Print the operation debug_id when logging an unexpected data version
> >       afs: Move key to afs_read struct
> >       afs: Don't truncate iter during data fetch
> >       afs: Log remote unmarshalling errors
> >       afs: Set up the iov_iter before calling afs_extract_data()
> >       afs: Use ITER_XARRAY for writing
> >       afs: Wait on PG_fscache before modifying/releasing a page
> >       afs: Extract writeback extension into its own function
> >       afs: Prepare for use of THPs
> >       afs: Use the fs operation ops to handle FetchData completion
> >       afs: Use new netfs lib read helper API
> >       afs: Use the netfs_write_begin() helper
> >
> > Matthew Wilcox (Oracle) (2):
> >       mm/filemap: Pass the file_ra_state in the ractl
> >       fs: Document file_ra_state
> >
> >
> >  Documentation/filesystems/index.rst         |    1 +
> >  Documentation/filesystems/netfs_library.rst |  526 ++++++++
> >  fs/Kconfig                                  |    1 +
> >  fs/Makefile                                 |    1 +
> >  fs/afs/Kconfig                              |    1 +
> >  fs/afs/dir.c                                |  225 ++--
> >  fs/afs/file.c                               |  483 ++------
> >  fs/afs/fs_operation.c                       |    4 +-
> >  fs/afs/fsclient.c                           |  108 +-
> >  fs/afs/inode.c                              |    7 +-
> >  fs/afs/internal.h                           |   59 +-
> >  fs/afs/rxrpc.c                              |  150 +--
> >  fs/afs/write.c                              |  657 +++++-----
> >  fs/afs/yfsclient.c                          |   82 +-
> >  fs/cachefiles/Makefile                      |    1 +
> >  fs/cachefiles/interface.c                   |    5 +-
> >  fs/cachefiles/internal.h                    |    9 +
> >  fs/cachefiles/io.c                          |  420 +++++++
> >  fs/ext4/verity.c                            |    2 +-
> >  fs/f2fs/file.c                              |    2 +-
> >  fs/f2fs/verity.c                            |    2 +-
> >  fs/fscache/Kconfig                          |    1 +
> >  fs/fscache/Makefile                         |    1 +
> >  fs/fscache/internal.h                       |    4 +
> >  fs/fscache/io.c                             |  116 ++
> >  fs/fscache/page.c                           |    2 +-
> >  fs/fscache/stats.c                          |    1 +
> >  fs/netfs/Kconfig                            |   23 +
> >  fs/netfs/Makefile                           |    5 +
> >  fs/netfs/internal.h                         |   97 ++
> >  fs/netfs/read_helper.c                      | 1185 +++++++++++++++++++
> >  fs/netfs/stats.c                            |   59 +
> >  include/linux/fs.h                          |   24 +-
> >  include/linux/fscache-cache.h               |    4 +
> >  include/linux/fscache.h                     |   50 +-
> >  include/linux/netfs.h                       |  234 ++++
> >  include/linux/pagemap.h                     |   41 +-
> >  include/net/af_rxrpc.h                      |    2 +-
> >  include/trace/events/afs.h                  |   74 +-
> >  include/trace/events/netfs.h                |  261 ++++
> >  mm/filemap.c                                |   63 +-
> >  mm/internal.h                               |    7 +-
> >  mm/readahead.c                              |   97 +-
> >  net/rxrpc/recvmsg.c                         |    9 +-
> >  44 files changed, 3998 insertions(+), 1108 deletions(-)
> >  create mode 100644 Documentation/filesystems/netfs_library.rst
> >  create mode 100644 fs/cachefiles/io.c
> >  create mode 100644 fs/fscache/io.c
> >  create mode 100644 fs/netfs/Kconfig
> >  create mode 100644 fs/netfs/Makefile
> >  create mode 100644 fs/netfs/internal.h
> >  create mode 100644 fs/netfs/read_helper.c
> >  create mode 100644 fs/netfs/stats.c
> >  create mode 100644 include/linux/netfs.h
> >  create mode 100644 include/trace/events/netfs.h
> >
> >
>
> Similar to Jeff, for most of first 16 patches (except patch 1 and 13)
> you can add
> Tested-by: Dave Wysochanski <dwysocha@redhat.com>
>

Clarification on patch 1.  You can include my "Tested-by" on that as well.
As you pointed out, the NFS patches used the new netfs API code paths
in read_helper.c which in turn use the iter-xarray patch, so my NFS
testing also covered patch 1.

My apologies for not looking more carefully.

> I rebased my latest NFS patches on top of your netfs-lib branch at the
> below commit (the 16th patch here)
> fce8d8a1ae46 fscache, cachefiles: Add alternate API to use kiocb for
> read/write to cache
>
> With netfs and fscache enabled mount, I ran the following tests, and
> found the series to be very solid, with no obvious failures (hangs,
> oopses, etc), and results matched tests run on vanilla 5.12-rc6:
> * unit tests: NFSv3, 4.0, 4.1, 4.2; localhost server; with/without all
> tracepoints enabled (fscache, cachefiles, netfs)
> * NFS connectathon: NFSv3, 4.0, 4.1, 4.2; rhel7 server; with/without
> all tracepoints enabled (fscache, cachefiles, netfs)
> * xfstests generic: NFSv3, 4.0, 4.1, 4.2; rhel7, rhel8 server
> Notes
> 1. I still have not resolved the pNFS issues so I did not run fscache
> enabled pNFS tests.
> 2. Current NFS patches do not use ITER_XARRAY (patch 1/30) or
> write_begin helper (patch 13/30)