Merge tag 'vfs-6.14-rc1.netfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Merge tag 'vfs-6.14-rc1.netfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull vfs netfs updates from Christian Brauner:
 "This contains read performance improvements and support for monolithic
  single-blob objects that have to be read/written as such (e.g. AFS
  directory contents). The implementation of the two parts is interwoven
  as each makes the other possible.

   - Read performance improvements

     The read performance improvements are intended to speed up some
     loss of performance detected in cifs and to a lesser extend in afs.

     The problem is that we queue too many work items during the
     collection of read results: each individual subrequest is collected
     by its own work item, and then they have to interact with each
     other when a series of subrequests don't exactly align with the
     pattern of folios that are being read by the overall request.

     Whilst the processing of the pages covered by individual
     subrequests as they complete potentially allows folios to be woken
     in parallel and with minimum delay, it can shuffle wakeups for
     sequential reads out of order - and that is the most common I/O
     pattern.

     The final assessment and cleanup of an operation is then held up
     until the last I/O completes - and for a synchronous sequential
     operation, this means the bouncing around of work items just adds
     latency.

     Two changes have been made to make this work:

     (1) All collection is now done in a single "work item" that works
         progressively through the subrequests as they complete (and
         also dispatches retries as necessary).

     (2) For readahead and AIO, this work item be done on a workqueue
         and can run in parallel with the ultimate consumer of the data;
         for synchronous direct or unbuffered reads, the collection is
         run in the application thread and not offloaded.

     Functions such as smb2_readv_callback() then just tell netfslib
     that the subrequest has terminated; netfslib does a minimal bit of
     processing on the spot - stat counting and tracing mostly - and
     then queues/wakes up the worker. This simplifies the logic as the
     collector just walks sequentially through the subrequests as they
     complete and walks through the folios, if buffered, unlocking them
     as it goes. It also keeps to a minimum the amount of latency
     injected into the filesystem's low-level I/O handling

     The way netfs supports filesystems using the deprecated
     PG_private_2 flag is changed: folios are flagged and added to a
     write request as they complete and that takes care of scheduling
     the writes to the cache. The originating read request can then just
     unlock the pages whatever happens.

   - Single-blob object support

     Single-blob objects are files for which the content of the file
     must be read from or written to the server in a single operation
     because reading them in parts may yield inconsistent results. AFS
     directories are an example of this as there exists the possibility
     that the contents are generated on the fly and would differ between
     reads or might change due to third party interference.

     Such objects will be written to and retrieved from the cache if one
     is present, though we allow/may need to propose multiple
     subrequests to do so. The important part is that read from/write to
     the *server* is monolithic.

     Single blob reading is, for the moment, fully synchronous and does
     result collection in the application thread and, also for the
     moment, the API is supplied the buffer in the form of a folio_queue
     chain rather than using the pagecache.

   - Related afs changes

     This series makes a number of changes to the kafs filesystem,
     primarily in the area of directory handling:

      - AFS's FetchData RPC reply processing is made partially
        asynchronous which allows the netfs_io_request's outstanding
        operation counter to be removed as part of reducing the
        collection to a single work item.

      - Directory and symlink reading are plumbed through netfslib using
        the single-blob object API and are now cacheable with fscache.
        This also allows the afs_read struct to be eliminated and
        netfs_io_subrequest to be used directly instead.

      - Directory and symlink content are now stored in a folio_queue
        buffer rather than in the pagecache. This means we don't require
        the RCU read lock and xarray iteration to access it, and folios
        won't randomly disappear under us because the VM wants them
        back.

      - The vnode operation lock is changed from a mutex struct to a
        private lock implementation. The problem is that the lock now
        needs to be dropped in a separate thread and mutexes don't
        permit that.

      - When a new directory or symlink is created, we now initialise it
        locally and mark it valid rather than downloading it (we know
        what it's likely to look like).

      - We now use the in-directory hashtable to reduce the number of
        entries we need to scan when doing a lookup. The edit routines
        have to maintain the hash chains.

      - Cancellation (e.g. by signal) of an async call after the
        rxrpc_call has been set up is now offloaded to the worker thread
        as there will be a notification from rxrpc upon completion. This
        avoids a double cleanup.

   - A "rolling buffer" implementation is created to abstract out the
     two separate folio_queue chaining implementations I had (one for
     read and one for write).

   - Functions are provided to create/extend a buffer in a folio_queue
     chain and tear it down again.

     This is used to handle AFS directories, but could also be used to
     create bounce buffers for content crypto and transport crypto.

   - The was_async argument is dropped from netfs_read_subreq_terminated()

     Instead we wake the read collection work item by either queuing it
     or waking up the app thread.

   - We don't need to use BH-excluding locks when communicating between
     the issuing thread and the collection thread as neither of them now
     run in BH context.

   - Also included are a number of new tracepoints; a split of the
     netfslib write collection code to put retrying into its own file
     (it gets more complicated with content encryption).

   - There are also some minor fixes AFS included, including fixing the
     AFS directory format struct layout, reducing some directory
     over-invalidation and making afs_mkdir() translate EEXIST to
     ENOTEMPY (which is not available on all systems the servers
     support).

   - Finally, there's a patch to try and detect entry into the folio
     unlock function with no folio_queue structs in the buffer (which
     isn't allowed in the cases that can get there).

     This is a debugging patch, but should be minimal overhead"

* tag 'vfs-6.14-rc1.netfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (31 commits)
  netfs: Report on NULL folioq in netfs_writeback_unlock_folios()
  afs: Add a tracepoint for afs_read_receive()
  afs: Locally initialise the contents of a new symlink on creation
  afs: Use the contained hashtable to search a directory
  afs: Make afs_mkdir() locally initialise a new directory's content
  netfs: Change the read result collector to only use one work item
  afs: Make {Y,}FS.FetchData an asynchronous operation
  afs: Fix cleanup of immediately failed async calls
  afs: Eliminate afs_read
  afs: Use netfslib for symlinks, allowing them to be cached
  afs: Use netfslib for directories
  afs: Make afs_init_request() get a key if not given a file
  netfs: Add support for caching single monolithic objects such as AFS dirs
  netfs: Add functions to build/clean a buffer in a folio_queue
  afs: Add more tracepoints to do with tracking validity
  cachefiles: Add auxiliary data trace
  cachefiles: Add some subrequest tracepoints
  netfs: Remove some extraneous directory invalidations
  afs: Fix directory format encoding struct
  afs: Fix EEXIST error returned from afs_rmdir() to be ENOTEMPTY
  ...