Create a dynamically sized pool of threads for doing very slow work items
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: David Howells <dhowells@redhat.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Steve Dickson <steved@redhat.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Daire Byrne <Daire.Byrne@framestore.com>
diff --git a/include/linux/slow-work.h b/include/linux/slow-work.h
new file mode 100644
index 0000000..4dd754a
--- /dev/null
+++ b/include/linux/slow-work.h
@@ -0,0 +1,88 @@
+/* Worker thread pool for slow items, such as filesystem lookups or mkdirs
+ *
+ * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#ifndef _LINUX_SLOW_WORK_H
+#define _LINUX_SLOW_WORK_H
+
+#ifdef CONFIG_SLOW_WORK
+
+struct slow_work;
+
+/*
+ * The operations used to support slow work items
+ */
+struct slow_work_ops {
+ /* get a ref on a work item
+ * - return 0 if successful, -ve if not
+ */
+ int (*get_ref)(struct slow_work *work);
+
+ /* discard a ref to a work item */
+ void (*put_ref)(struct slow_work *work);
+
+ /* execute a work item */
+ void (*execute)(struct slow_work *work);
+};
+
+/*
+ * A slow work item
+ * - A reference is held on the parent object by the thread pool when it is
+ * queued
+ */
+struct slow_work {
+ unsigned long flags;
+#define SLOW_WORK_PENDING 0 /* item pending (further) execution */
+#define SLOW_WORK_EXECUTING 1 /* item currently executing */
+#define SLOW_WORK_ENQ_DEFERRED 2 /* item enqueue deferred */
+#define SLOW_WORK_VERY_SLOW 3 /* item is very slow */
+ const struct slow_work_ops *ops; /* operations table for this item */
+ struct list_head link; /* link in queue */
+};
+
+/**
+ * slow_work_init - Initialise a slow work item
+ * @work: The work item to initialise
+ * @ops: The operations to use to handle the slow work item
+ *
+ * Initialise a slow work item.
+ */
+static inline void slow_work_init(struct slow_work *work,
+ const struct slow_work_ops *ops)
+{
+ work->flags = 0;
+ work->ops = ops;
+ INIT_LIST_HEAD(&work->link);
+}
+
+/**
+ * slow_work_init - Initialise a very slow work item
+ * @work: The work item to initialise
+ * @ops: The operations to use to handle the slow work item
+ *
+ * Initialise a very slow work item. This item will be restricted such that
+ * only a certain number of the pool threads will be able to execute items of
+ * this type.
+ */
+static inline void vslow_work_init(struct slow_work *work,
+ const struct slow_work_ops *ops)
+{
+ work->flags = 1 << SLOW_WORK_VERY_SLOW;
+ work->ops = ops;
+ INIT_LIST_HEAD(&work->link);
+}
+
+extern int slow_work_enqueue(struct slow_work *work);
+extern int slow_work_register_user(void);
+extern void slow_work_unregister_user(void);
+
+
+#endif /* CONFIG_SLOW_WORK */
+#endif /* _LINUX_SLOW_WORK_H */