Re: [RFC][PATCH 00/25] Network fs helper library & fscache kiocb API

J. Bruce Fields
2021-01-21T16:48:47Z

On Wed, Jan 20, 2021 at 10:21:24PM +0000, David Howells wrote:
> 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.

What are the consequences from the point of view of a user?

--b.

>
> 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 four 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.
>
> 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.
>
> These patches can be found also on:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=fscache-netfs-lib
>
> David
> ---
> David Howells (24):
> iov_iter: Add ITER_XARRAY
> vm: Add wait/unlock functions for PG_fscache
> mm: Implement readahead_control pageset expansion
> vfs: Export rw_verify_area() for use by cachefiles
> netfs: Make a netfs helper module
> 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
> 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 fscache read helper API
>
> Takashi Iwai (1):
> cachefiles: Drop superfluous readpages aops NULL check
>
>
> fs/Kconfig | 1 +
> fs/Makefile | 1 +
> fs/afs/Kconfig | 1 +
> fs/afs/dir.c | 225 ++++---
> fs/afs/file.c | 472 ++++----------
> fs/afs/fs_operation.c | 4 +-
> fs/afs/fsclient.c | 108 ++--
> fs/afs/inode.c | 7 +-
> fs/afs/internal.h | 57 +-
> fs/afs/rxrpc.c | 150 ++---
> fs/afs/write.c | 610 ++++++++++--------
> fs/afs/yfsclient.c | 82 +--
> fs/cachefiles/Makefile | 1 +
> fs/cachefiles/interface.c | 5 +-
> fs/cachefiles/internal.h | 9 +
> fs/cachefiles/rdwr.c | 2 -
> fs/cachefiles/rdwr2.c | 406 ++++++++++++
> fs/fscache/Makefile | 3 +-
> fs/fscache/internal.h | 3 +
> fs/fscache/page.c | 2 +-
> fs/fscache/page2.c | 116 ++++
> fs/fscache/stats.c | 1 +
> fs/internal.h | 5 -
> fs/netfs/Kconfig | 23 +
> fs/netfs/Makefile | 5 +
> fs/netfs/internal.h | 97 +++
> fs/netfs/read_helper.c | 1142 +++++++++++++++++++++++++++++++++
> fs/netfs/stats.c | 57 ++
> fs/read_write.c | 1 +
> include/linux/fs.h | 1 +
> include/linux/fscache-cache.h | 4 +
> include/linux/fscache.h | 28 +-
> include/linux/netfs.h | 167 +++++
> include/linux/pagemap.h | 16 +
> include/net/af_rxrpc.h | 2 +-
> include/trace/events/afs.h | 74 +--
> include/trace/events/netfs.h | 201 ++++++
> mm/filemap.c | 18 +
> mm/readahead.c | 70 ++
> net/rxrpc/recvmsg.c | 9 +-
> 40 files changed, 3171 insertions(+), 1015 deletions(-)
> create mode 100644 fs/cachefiles/rdwr2.c
> create mode 100644 fs/fscache/page2.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
>