srcu: Begin offloading srcu_struct fields to srcu_update

The current srcu_struct structure is on the order of 200 bytes in size
(depending on architecture and .config), which is much better than the
old-style 26K bytes, but still all too inconvenient when one is trying
to achieve good cache locality on a fastpath involving SRCU readers.

However, only a few fields in srcu_struct are used by SRCU readers.
The remaining fields could be offloaded to a new srcu_update
structure, thus shrinking the srcu_struct structure down to a few
tens of bytes.  This commit begins this noble quest, a quest that is
complicated by open-coded initialization of the srcu_struct within the
srcu_notifier_head structure.  This complication is addressed by updating
the srcu_notifier_head structure's open coding, given that there does
not appear to be a straightforward way of abstracting that initialization.

This commit moves only the ->node pointer to srcu_update.  Later commits
will move additional fields.

[ paulmck: Fold in qiang1.zhang@intel.com's memory-leak fix. ]

Link: https://lore.kernel.org/all/20230320055751.4120251-1-qiang1.zhang@intel.com/
Suggested-by: Christoph Hellwig <hch@lst.de>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Tested-by: Sachin Sant <sachinp@linux.ibm.com>
Tested-by: "Zhang, Qiang1" <qiang1.zhang@intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 5aa5e0faf6a1..ebd72491af99 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -31,7 +31,7 @@ struct srcu_struct {
 
 void srcu_drive_gp(struct work_struct *wp);
 
-#define __SRCU_STRUCT_INIT(name, __ignored)				\
+#define __SRCU_STRUCT_INIT(name, __ignored, ___ignored)			\
 {									\
 	.srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq),	\
 	.srcu_cb_tail = &name.srcu_cb_head,				\
@@ -44,9 +44,9 @@ void srcu_drive_gp(struct work_struct *wp);
  * Tree SRCU, which needs some per-CPU data.
  */
 #define DEFINE_SRCU(name) \
-	struct srcu_struct name = __SRCU_STRUCT_INIT(name, name)
+	struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name)
 #define DEFINE_STATIC_SRCU(name) \
-	static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name)
+	static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name)
 
 void synchronize_srcu(struct srcu_struct *ssp);