padata: allocate work structures for parallel jobs from a pool

padata allocates per-CPU, per-instance work structs for parallel jobs.  A
do_parallel call assigns a job to a sequence number and hashes the number
to a CPU, where the job will eventually run using the corresponding work.

This approach fit with how padata used to bind a job to each CPU
round-robin, makes less sense after commit bfde23ce200e6 ("padata: unbind
parallel jobs from specific CPUs") because a work isn't bound to a
particular CPU anymore, and isn't needed at all for multithreaded jobs
because they don't have sequence numbers.

Replace the per-CPU works with a preallocated pool, which allows sharing
them between existing padata users and the upcoming multithreaded user.
The pool will also facilitate setting NUMA-aware concurrency limits with
later users.

The pool is sized according to the number of possible CPUs.  With this
limit, MAX_OBJ_NUM no longer makes sense, so remove it.

If the global pool is exhausted, a parallel job is run in the current task
instead to throttle a system trying to do too much in parallel.

Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Josh Triplett <josh@joshtriplett.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Robert Elliott <elliott@hpe.com>
Cc: Shile Zhang <shile.zhang@linux.alibaba.com>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: Steven Sistare <steven.sistare@oracle.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Link: http://lkml.kernel.org/r/20200527173608.2885243-4-daniel.m.jordan@oracle.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 7 deletions

diff --git a/include/linux/padata.h b/include/linux/padata.h
index d50bd1a7756f..b4da88f8588c 100644
--- a/include/linux/padata.h
+++ b/include/linux/padata.h
@@ -24,7 +24,6 @@
  * @list: List entry, to attach to the padata lists.
  * @pd: Pointer to the internal control structure.
  * @cb_cpu: Callback cpu for serializatioon.
- * @cpu: Cpu for parallelization.
  * @seq_nr: Sequence number of the parallelized data object.
  * @info: Used to pass information from the parallel to the serial function.
  * @parallel: Parallel execution function.
@@ -34,7 +33,6 @@ struct padata_priv {
 	struct list_head	list;
 	struct parallel_data	*pd;
 	int			cb_cpu;
-	int			cpu;
 	unsigned int		seq_nr;
 	int			info;
 	void                    (*parallel)(struct padata_priv *padata);
@@ -68,15 +66,11 @@ struct padata_serial_queue {
 /**
  * struct padata_parallel_queue - The percpu padata parallel queue
  *
- * @parallel: List to wait for parallelization.
  * @reorder: List to wait for reordering after parallel processing.
- * @work: work struct for parallelization.
  * @num_obj: Number of objects that are processed by this cpu.
  */
 struct padata_parallel_queue {
-       struct padata_list    parallel;
        struct padata_list    reorder;
-       struct work_struct    work;
        atomic_t              num_obj;
 };
 
@@ -111,7 +105,7 @@ struct parallel_data {
 	struct padata_parallel_queue	__percpu *pqueue;
 	struct padata_serial_queue	__percpu *squeue;
 	atomic_t			refcnt;
-	atomic_t			seq_nr;
+	unsigned int			seq_nr;
 	unsigned int			processed;
 	int				cpu;
 	struct padata_cpumask		cpumask;