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

Make fscache object state transition callbacks use workqueue instead
of slow-work.  New dedicated unbound CPU workqueue fscache_object_wq
is created.  get/put callbacks are renamed and modified to take
@object and called directly from the enqueue wrapper and the work
function.  While at it, make all open coded instances of get/put to
use fscache_get/put_object().

* Unbound workqueue is used.

* work_busy() output is printed instead of slow-work flags in object
  debugging outputs.  They mean basically the same thing bit-for-bit.

* sysctl fscache.object_max_active added to control concurrency.  The
  default value is nr_cpus clamped between 4 and
  WQ_UNBOUND_MAX_ACTIVE.

* slow_work_sleep_till_thread_needed() is replaced with fscache
  private implementation fscache_object_sleep_till_congested() which
  waits on fscache_object_wq congestion.

* 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, 76 insertions, 0 deletions

diff --git a/fs/fscache/main.c b/fs/fscache/main.c
index add6bdb53f04..bb8d4c35c7a2 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -15,6 +15,7 @@
 #include <linux/sched.h>
 #include <linux/completion.h>
 #include <linux/slab.h>
+#include <linux/seq_file.h>
 #include "internal.h"
 
 MODULE_DESCRIPTION("FS Cache Manager");
@@ -40,22 +41,89 @@ MODULE_PARM_DESC(fscache_debug,
                  "FS-Cache debugging mask");
 
 struct kobject *fscache_root;
+struct workqueue_struct *fscache_object_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;
+
+#ifdef CONFIG_SYSCTL
+static struct ctl_table_header *fscache_sysctl_header;
+
+static int fscache_max_active_sysctl(struct ctl_table *table, int write,
+                                     void __user *buffer,
+                                     size_t *lenp, loff_t *ppos)
+{
+        struct workqueue_struct **wqp = table->extra1;
+        unsigned int *datap = table->data;
+        int ret;
+
+        ret = proc_dointvec(table, write, buffer, lenp, ppos);
+        if (ret == 0)
+                workqueue_set_max_active(*wqp, *datap);
+        return ret;
+}
+
+ctl_table fscache_sysctls[] = {
+        {
+                .procname       = "object_max_active",
+                .data           = &fscache_object_max_active,
+                .maxlen         = sizeof(unsigned),
+                .mode           = 0644,
+                .proc_handler   = fscache_max_active_sysctl,
+                .extra1         = &fscache_object_wq,
+        },
+        {}
+};
+
+ctl_table fscache_sysctls_root[] = {
+        {
+                .procname       = "fscache",
+                .mode           = 0555,
+                .child          = fscache_sysctls,
+        },
+        {}
+};
+#endif
 
 /*
  * initialise the fs caching module
  */
 static int __init fscache_init(void)
 {
+        unsigned int nr_cpus = num_possible_cpus();
+        unsigned int cpu;
         int ret;
 
         ret = slow_work_register_user(THIS_MODULE);
         if (ret < 0)
                 goto error_slow_work;
 
+        fscache_object_max_active =
+                clamp_val(nr_cpus,
+                          fscache_object_max_active, WQ_UNBOUND_MAX_ACTIVE);
+
+        ret = -ENOMEM;
+        fscache_object_wq = alloc_workqueue("fscache_object", WQ_UNBOUND,
+                                            fscache_object_max_active);
+        if (!fscache_object_wq)
+                goto error_object_wq;
+
+        for_each_possible_cpu(cpu)
+                init_waitqueue_head(&per_cpu(fscache_object_cong_wait, cpu));
+
         ret = fscache_proc_init();
         if (ret < 0)
                 goto error_proc;
 
+#ifdef CONFIG_SYSCTL
+        ret = -ENOMEM;
+        fscache_sysctl_header = register_sysctl_table(fscache_sysctls_root);
+        if (!fscache_sysctl_header)
+                goto error_sysctl;
+#endif
+
         fscache_cookie_jar = kmem_cache_create("fscache_cookie_jar",
                                                sizeof(struct fscache_cookie),
                                                0,
@@ -78,8 +146,14 @@ static int __init fscache_init(void)
 error_kobj:
         kmem_cache_destroy(fscache_cookie_jar);
 error_cookie_jar:
+#ifdef CONFIG_SYSCTL
+        unregister_sysctl_table(fscache_sysctl_header);
+error_sysctl:
+#endif
         fscache_proc_cleanup();
 error_proc:
+        destroy_workqueue(fscache_object_wq);
+error_object_wq:
         slow_work_unregister_user(THIS_MODULE);
 error_slow_work:
         return ret;
@@ -96,7 +170,9 @@ static void __exit fscache_exit(void)
 
         kobject_put(fscache_root);
         kmem_cache_destroy(fscache_cookie_jar);
+        unregister_sysctl_table(fscache_sysctl_header);
         fscache_proc_cleanup();
+        destroy_workqueue(fscache_object_wq);
         slow_work_unregister_user(THIS_MODULE);
         printk(KERN_NOTICE "FS-Cache: Unloaded\n");
 }