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Date: Thu, 25 May 2017 14:59:41 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 68/88] srcu: Apply trivial callback lists to shrink Tiny SRCU
The rcu_segcblist structure provides quite a bit of functionality, and
Tiny SRCU needs almost none of it. So this commit replaces Tiny SRCU's
uses of rcu_segcblist with a simple singly linked list with tail pointer.
This change significantly reduces Tiny SRCU's memory footprint, more
than making up for the growth caused by the creation of rcu_segcblist.c
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
include/linux/srcutiny.h | 7 +++--
init/Kconfig | 2 +-
kernel/rcu/rcu.h | 2 +-
kernel/rcu/srcutiny.c | 70 ++++++++++++++++++++++--------------------------
4 files changed, 37 insertions(+), 44 deletions(-)
diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index c205b8dd7a6a..01519bcf7634 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -33,9 +33,8 @@ struct srcu_struct {
u8 srcu_gp_waiting; /* GP waiting for readers? */
struct swait_queue_head srcu_wq;
/* Last srcu_read_unlock() wakes GP. */
- unsigned long srcu_gp_seq; /* GP seq # for callback tagging. */
- struct rcu_segcblist srcu_cblist;
- /* Pending SRCU callbacks. */
+ struct rcu_head *srcu_cb_head; /* Pending callbacks: Head. */
+ struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
struct work_struct srcu_work; /* For driving grace periods. */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
@@ -47,7 +46,7 @@ void srcu_drive_gp(struct work_struct *wp);
#define __SRCU_STRUCT_INIT(name) \
{ \
.srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq), \
- .srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist), \
+ .srcu_cb_tail = &name.srcu_cb_head, \
.srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
__SRCU_DEP_MAP_INIT(name) \
}
diff --git a/init/Kconfig b/init/Kconfig
index d928a3724af9..a2cfde19e8b8 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -573,7 +573,7 @@ config RCU_STALL_COMMON
making these warnings mandatory for the tree variants.
config RCU_NEED_SEGCBLIST
- def_bool ( TREE_RCU || PREEMPT_RCU || TINY_SRCU || TREE_SRCU )
+ def_bool ( TREE_RCU || PREEMPT_RCU || TREE_SRCU )
config CONTEXT_TRACKING
bool
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 74d9fc205313..6a1e85bd2eac 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -398,7 +398,7 @@ static inline void srcutorture_get_gp_data(enum rcutorture_type test_type,
if (test_type != SRCU_FLAVOR)
return;
*flags = 0;
- *completed = sp->srcu_gp_seq;
+ *completed = sp->srcu_idx;
*gpnum = *completed;
}
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index fe0b16db2aae..178822342689 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -38,8 +38,8 @@ static int init_srcu_struct_fields(struct srcu_struct *sp)
sp->srcu_lock_nesting[0] = 0;
sp->srcu_lock_nesting[1] = 0;
init_swait_queue_head(&sp->srcu_wq);
- sp->srcu_gp_seq = 0;
- rcu_segcblist_init(&sp->srcu_cblist);
+ sp->srcu_cb_head = NULL;
+ sp->srcu_cb_tail = &sp->srcu_cb_head;
sp->srcu_gp_running = false;
sp->srcu_gp_waiting = false;
sp->srcu_idx = 0;
@@ -88,10 +88,10 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
{
WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
flush_work(&sp->srcu_work);
- WARN_ON(rcu_seq_state(sp->srcu_gp_seq));
WARN_ON(sp->srcu_gp_running);
WARN_ON(sp->srcu_gp_waiting);
- WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist));
+ WARN_ON(sp->srcu_cb_head);
+ WARN_ON(&sp->srcu_cb_head != sp->srcu_cb_tail);
}
EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
@@ -117,52 +117,44 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
void srcu_drive_gp(struct work_struct *wp)
{
int idx;
- struct rcu_cblist ready_cbs;
- struct srcu_struct *sp;
+ struct rcu_head *lh;
struct rcu_head *rhp;
+ struct srcu_struct *sp;
sp = container_of(wp, struct srcu_struct, srcu_work);
- if (sp->srcu_gp_running || rcu_segcblist_empty(&sp->srcu_cblist))
+ if (sp->srcu_gp_running || !READ_ONCE(sp->srcu_cb_head))
return; /* Already running or nothing to do. */
- /* Tag recently arrived callbacks and wait for readers. */
+ /* Remove recently arrived callbacks and wait for readers. */
WRITE_ONCE(sp->srcu_gp_running, true);
- rcu_segcblist_accelerate(&sp->srcu_cblist,
- rcu_seq_snap(&sp->srcu_gp_seq));
- rcu_seq_start(&sp->srcu_gp_seq);
+ local_irq_disable();
+ lh = sp->srcu_cb_head;
+ sp->srcu_cb_head = NULL;
+ sp->srcu_cb_tail = &sp->srcu_cb_head;
+ local_irq_enable();
idx = sp->srcu_idx;
WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx);
WRITE_ONCE(sp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */
swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx]));
WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
- rcu_seq_end(&sp->srcu_gp_seq);
-
- /* Update callback list based on GP, and invoke ready callbacks. */
- rcu_segcblist_advance(&sp->srcu_cblist,
- rcu_seq_current(&sp->srcu_gp_seq));
- if (rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
- rcu_cblist_init(&ready_cbs);
- local_irq_disable();
- rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
- local_irq_enable();
- rhp = rcu_cblist_dequeue(&ready_cbs);
- for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
- local_bh_disable();
- rhp->func(rhp);
- local_bh_enable();
- }
- local_irq_disable();
- rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
- local_irq_enable();
+
+ /* Invoke the callbacks we removed above. */
+ while (lh) {
+ rhp = lh;
+ lh = lh->next;
+ local_bh_disable();
+ rhp->func(rhp);
+ local_bh_enable();
}
- WRITE_ONCE(sp->srcu_gp_running, false);
/*
- * If more callbacks, reschedule ourselves. This can race with
- * a call_srcu() at interrupt level, but the ->srcu_gp_running
- * checks will straighten that out.
+ * Enable rescheduling, and if there are more callbacks,
+ * reschedule ourselves. This can race with a call_srcu()
+ * at interrupt level, but the ->srcu_gp_running checks will
+ * straighten that out.
*/
- if (!rcu_segcblist_empty(&sp->srcu_cblist))
+ WRITE_ONCE(sp->srcu_gp_running, false);
+ if (READ_ONCE(sp->srcu_cb_head))
schedule_work(&sp->srcu_work);
}
EXPORT_SYMBOL_GPL(srcu_drive_gp);
@@ -171,14 +163,16 @@ EXPORT_SYMBOL_GPL(srcu_drive_gp);
* Enqueue an SRCU callback on the specified srcu_struct structure,
* initiating grace-period processing if it is not already running.
*/
-void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
+void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
rcu_callback_t func)
{
unsigned long flags;
- head->func = func;
+ rhp->func = func;
+ rhp->next = NULL;
local_irq_save(flags);
- rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
+ *sp->srcu_cb_tail = rhp;
+ sp->srcu_cb_tail = &rhp->next;
local_irq_restore(flags);
if (!READ_ONCE(sp->srcu_gp_running))
schedule_work(&sp->srcu_work);
--
2.5.2
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