[PATCH] Add SRCU-based notifier chains

This patch (as751) adds a new type of notifier chain, based on the SRCU
(Sleepable Read-Copy Update) primitives recently added to the kernel.  An
SRCU notifier chain is much like a blocking notifier chain, in that it must
be called in process context and its callout routines are allowed to sleep.
 The difference is that the chain's links are protected by the SRCU
mechanism rather than by an rw-semaphore, so calling the chain has
extremely low overhead: no memory barriers and no cache-line bouncing.  On
the other hand, unregistering from the chain is expensive and the chain
head requires special runtime initialization (plus cleanup if it is to be
deallocated).

SRCU notifiers are appropriate for notifiers that will be called very
frequently and for which unregistration occurs very seldom.  The proposed
"task notifier" scheme qualifies, as may some of the network notifiers.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Paul E. McKenney <paulmck@us.ibm.com>
Acked-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 947fdab2ddb0..8a45367b5f3a 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -24,6 +24,9 @@
  *
  */
 
+#ifndef _LINUX_SRCU_H
+#define _LINUX_SRCU_H
+
 struct srcu_struct_array {
         int c[2];
 };
@@ -46,4 +49,5 @@ int srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 void srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 void synchronize_srcu(struct srcu_struct *sp);
 long srcu_batches_completed(struct srcu_struct *sp);
-void cleanup_srcu_struct(struct srcu_struct *sp);
+
+#endif