fscache: convert operation to use workqueue instead of slow-work

Make fscache operation to use only workqueue instead of combination of
workqueue and slow-work.  FSCACHE_OP_SLOW is dropped and
FSCACHE_OP_FAST is renamed to FSCACHE_OP_ASYNC and uses newly added
fscache_op_wq workqueue to execute op->processor().
fscache_operation_init_slow() is dropped and fscache_operation_init()
now takes @processor argument directly.

* Unbound workqueue is used.

* fscache_retrieval_work() is no longer necessary as OP_ASYNC now does
  the equivalent thing.

* sysctl fscache.operation_max_active added to control concurrency.
  The default value is nr_cpus clamped between 2 and
  WQ_UNBOUND_MAX_ACTIVE.

* debugfs support is dropped for now.  Tracing API based debug
  facility is planned to be added.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Howells <dhowells@redhat.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/fs/fscache/main.c b/fs/fscache/main.c
index bb8d4c35c7a2..44d13ddab2cc 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -42,11 +42,13 @@ MODULE_PARM_DESC(fscache_debug,
 
 struct kobject *fscache_root;
 struct workqueue_struct *fscache_object_wq;
+struct workqueue_struct *fscache_op_wq;
 
 DEFINE_PER_CPU(wait_queue_head_t, fscache_object_cong_wait);
 
 /* these values serve as lower bounds, will be adjusted in fscache_init() */
 static unsigned fscache_object_max_active = 4;
+static unsigned fscache_op_max_active = 2;
 
 #ifdef CONFIG_SYSCTL
 static struct ctl_table_header *fscache_sysctl_header;
@@ -74,6 +76,14 @@ ctl_table fscache_sysctls[] = {
                 .proc_handler   = fscache_max_active_sysctl,
                 .extra1         = &fscache_object_wq,
         },
+        {
+                .procname       = "operation_max_active",
+                .data           = &fscache_op_max_active,
+                .maxlen         = sizeof(unsigned),
+                .mode           = 0644,
+                .proc_handler   = fscache_max_active_sysctl,
+                .extra1         = &fscache_op_wq,
+        },
         {}
 };
 
@@ -110,6 +120,16 @@ static int __init fscache_init(void)
         if (!fscache_object_wq)
                 goto error_object_wq;
 
+        fscache_op_max_active =
+                clamp_val(fscache_object_max_active / 2,
+                          fscache_op_max_active, WQ_UNBOUND_MAX_ACTIVE);
+
+        ret = -ENOMEM;
+        fscache_op_wq = alloc_workqueue("fscache_operation", WQ_UNBOUND,
+                                        fscache_op_max_active);
+        if (!fscache_op_wq)
+                goto error_op_wq;
+
         for_each_possible_cpu(cpu)
                 init_waitqueue_head(&per_cpu(fscache_object_cong_wait, cpu));
 
@@ -152,6 +172,8 @@ error_sysctl:
 #endif
         fscache_proc_cleanup();
 error_proc:
+        destroy_workqueue(fscache_op_wq);
+error_op_wq:
         destroy_workqueue(fscache_object_wq);
 error_object_wq:
         slow_work_unregister_user(THIS_MODULE);
@@ -172,6 +194,7 @@ static void __exit fscache_exit(void)
         kmem_cache_destroy(fscache_cookie_jar);
         unregister_sysctl_table(fscache_sysctl_header);
         fscache_proc_cleanup();
+        destroy_workqueue(fscache_op_wq);
         destroy_workqueue(fscache_object_wq);
         slow_work_unregister_user(THIS_MODULE);
         printk(KERN_NOTICE "FS-Cache: Unloaded\n");