This adds support for starting slow work with a delay, similar
to the functionality we have for workqueues.
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Add support for cancellation of queued slow work and delayed slow work items.
The cancellation functions will wait for items that are pending or undergoing
execution to be discarded by the slow work facility.

Attempting to enqueue work that is in the process of being cancelled will
result in ECANCELED.
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Wait for outstanding slow work items belonging to a module to clear when
unregistering that module as a user of the facility.  This prevents the put_ref
code of a work item from being taken away before it returns.
Signed-off-by: NDavid Howells <dhowells@redhat.com>

Fix a comment typo in slow-work.h

...a trivial mistake, but it will mess up kerneldoc if nothing else.
Signed-off-by: NJonathan Corbet <corbet@lwn.net>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Document the slow work thread pool.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Make the slow work pool configurable through /proc/sys/kernel/slow-work.

 (*) /proc/sys/kernel/slow-work/min-threads

     The minimum number of threads that should be in the pool as long as it is
     in use.  This may be anywhere between 2 and max-threads.

 (*) /proc/sys/kernel/slow-work/max-threads

     The maximum number of threads that should in the pool.  This may be
     anywhere between min-threads and 255 or NR_CPUS * 2, whichever is greater.

 (*) /proc/sys/kernel/slow-work/vslow-percentage

     The percentage of active threads in the pool that may be used to execute
     very slow work items.  This may be between 1 and 99.  The resultant number
     is bounded to between 1 and one fewer than the number of active threads.
     This ensures there is always at least one thread that can process very
     slow work items, and always at least one thread that won't.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSerge Hallyn <serue@us.ibm.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>

Create a dynamically sized pool of threads for doing very slow work items, such
as invoking mkdir() or rmdir() - things that may take a long time and may
sleep, holding mutexes/semaphores and hogging a thread, and are thus unsuitable
for workqueues.

The number of threads is always at least a settable minimum, but more are
started when there's more work to do, up to a limit.  Because of the nature of
the load, it's not suitable for a 1-thread-per-CPU type pool.  A system with
one CPU may well want several threads.

This is used by FS-Cache to do slow caching operations in the background, such
as looking up, creating or deleting cache objects.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NSerge Hallyn <serue@us.ibm.com>
Acked-by: NSteve Dickson <steved@redhat.com>
Acked-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NDaire Byrne <Daire.Byrne@framestore.com>