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, 8 insertions, 28 deletions

diff --git a/fs/fscache/page.c b/fs/fscache/page.c
index 723b889fd219..41c441c2058d 100644
--- a/fs/fscache/page.c
+++ b/fs/fscache/page.c
@@ -105,7 +105,7 @@ bool __fscache_maybe_release_page(struct fscache_cookie *cookie,
 
 page_busy:
         /* we might want to wait here, but that could deadlock the allocator as
-         * the slow-work threads writing to the cache may all end up sleeping
+         * the work threads writing to the cache may all end up sleeping
          * on memory allocation */
         fscache_stat(&fscache_n_store_vmscan_busy);
         return false;
@@ -188,9 +188,8 @@ int __fscache_attr_changed(struct fscache_cookie *cookie)
                 return -ENOMEM;
         }
 
-        fscache_operation_init(op, NULL);
-        fscache_operation_init_slow(op, fscache_attr_changed_op);
-        op->flags = FSCACHE_OP_SLOW | (1 << FSCACHE_OP_EXCLUSIVE);
+        fscache_operation_init(op, fscache_attr_changed_op, NULL);
+        op->flags = FSCACHE_OP_ASYNC | (1 << FSCACHE_OP_EXCLUSIVE);
         fscache_set_op_name(op, "Attr");
 
         spin_lock(&cookie->lock);
@@ -218,24 +217,6 @@ nobufs:
 EXPORT_SYMBOL(__fscache_attr_changed);
 
 /*
- * handle secondary execution given to a retrieval op on behalf of the
- * cache
- */
-static void fscache_retrieval_work(struct work_struct *work)
-{
-        struct fscache_retrieval *op =
-                container_of(work, struct fscache_retrieval, op.fast_work);
-        unsigned long start;
-
-        _enter("{OP%x}", op->op.debug_id);
-
-        start = jiffies;
-        op->op.processor(&op->op);
-        fscache_hist(fscache_ops_histogram, start);
-        fscache_put_operation(&op->op);
-}
-
-/*
  * release a retrieval op reference
  */
 static void fscache_release_retrieval_op(struct fscache_operation *_op)
@@ -269,13 +250,12 @@ static struct fscache_retrieval *fscache_alloc_retrieval(
                 return NULL;
         }
 
-        fscache_operation_init(&op->op, fscache_release_retrieval_op);
+        fscache_operation_init(&op->op, NULL, fscache_release_retrieval_op);
         op->op.flags    = FSCACHE_OP_MYTHREAD | (1 << FSCACHE_OP_WAITING);
         op->mapping     = mapping;
         op->end_io_func = end_io_func;
         op->context     = context;
         op->start_time  = jiffies;
-        INIT_WORK(&op->op.fast_work, fscache_retrieval_work);
         INIT_LIST_HEAD(&op->to_do);
         fscache_set_op_name(&op->op, "Retr");
         return op;
@@ -795,9 +775,9 @@ int __fscache_write_page(struct fscache_cookie *cookie,
         if (!op)
                 goto nomem;
 
-        fscache_operation_init(&op->op, fscache_release_write_op);
-        fscache_operation_init_slow(&op->op, fscache_write_op);
-        op->op.flags = FSCACHE_OP_SLOW | (1 << FSCACHE_OP_WAITING);
+        fscache_operation_init(&op->op, fscache_write_op,
+                               fscache_release_write_op);
+        op->op.flags = FSCACHE_OP_ASYNC | (1 << FSCACHE_OP_WAITING);
         fscache_set_op_name(&op->op, "Write1");
 
         ret = radix_tree_preload(gfp & ~__GFP_HIGHMEM);
@@ -852,7 +832,7 @@ int __fscache_write_page(struct fscache_cookie *cookie,
         fscache_stat(&fscache_n_store_ops);
         fscache_stat(&fscache_n_stores_ok);
 
-        /* the slow work queue now carries its own ref on the object */
+        /* the work queue now carries its own ref on the object */
         fscache_put_operation(&op->op);
         _leave(" = 0");
         return 0;