[PATCH tip/core/rcu 3/3] srcu: Make early-boot call_srcu() reuse workqueue lists

Paul E. McKenney
2018-08-29T21:23:32Z

Allocating a list_head structure that is almost never used, and, when
used, is used only during early boot (rcu_init() and earlier), is a bit
wasteful. This commit therefore eliminates that list_head in favor of
the one in the work_struct structure. This is safe because the work_struct
structure cannot be used until after rcu_init() returns.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
---
include/linux/srcutiny.h | 2 --
include/linux/srcutree.h | 3 +--
kernel/rcu/srcutiny.c | 10 +++++-----
kernel/rcu/srcutree.c | 11 +++++------
4 files changed, 11 insertions(+), 15 deletions(-)

diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 2b5c0822e683..f41d2fb09f87 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -36,7 +36,6 @@ struct srcu_struct {
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. */
- struct list_head srcu_boot_entry; /* Early-boot callbacks. */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
@@ -49,7 +48,6 @@ void srcu_drive_gp(struct work_struct *wp);
.srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq), \
.srcu_cb_tail = &name.srcu_cb_head, \
.srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
- .srcu_boot_entry = LIST_HEAD_INIT(name.srcu_boot_entry), \
__SRCU_DEP_MAP_INIT(name) \
}

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 9cfa4610113a..0ae91b3a7406 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -94,7 +94,6 @@ struct srcu_struct {
/* callback for the barrier */
/* operation. */
struct delayed_work work;
- struct list_head srcu_boot_entry; /* Early-boot callbacks. */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
@@ -110,7 +109,7 @@ struct srcu_struct {
.sda = &pcpu_name, \
.lock = __SPIN_LOCK_UNLOCKED(name.lock), \
.srcu_gp_seq_needed = -1UL, \
- .srcu_boot_entry = LIST_HEAD_INIT(name.srcu_boot_entry), \
+ .work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0), \
__SRCU_DEP_MAP_INIT(name) \
}

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index d233f0c63f6f..b46e6683f8c9 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -48,7 +48,7 @@ static int init_srcu_struct_fields(struct srcu_struct *sp)
sp->srcu_gp_waiting = false;
sp->srcu_idx = 0;
INIT_WORK(&sp->srcu_work, srcu_drive_gp);
- INIT_LIST_HEAD(&sp->srcu_boot_entry);
+ INIT_LIST_HEAD(&sp->srcu_work.entry);
return 0;
}

@@ -185,8 +185,8 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
if (!READ_ONCE(sp->srcu_gp_running)) {
if (likely(srcu_init_done))
schedule_work(&sp->srcu_work);
- else if (list_empty(&sp->srcu_boot_entry))
- list_add(&sp->srcu_boot_entry, &srcu_boot_list);
+ else if (list_empty(&sp->srcu_work.entry))
+ list_add(&sp->srcu_work.entry, &srcu_boot_list);
}
}
EXPORT_SYMBOL_GPL(call_srcu);
@@ -224,8 +224,8 @@ void __init srcu_init(void)
srcu_init_done = true;
while (!list_empty(&srcu_boot_list)) {
sp = list_first_entry(&srcu_boot_list,
- struct srcu_struct, srcu_boot_entry);
- list_del_init(&sp->srcu_boot_entry);
+ struct srcu_struct, srcu_work.entry);
+ list_del_init(&sp->srcu_work.entry);
schedule_work(&sp->srcu_work);
}
}
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index e79c1929328f..36a2857c84e0 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -186,7 +186,6 @@ static int init_srcu_struct_fields(struct srcu_struct *sp, bool is_static)
mutex_init(&sp->srcu_barrier_mutex);
atomic_set(&sp->srcu_barrier_cpu_cnt, 0);
INIT_DELAYED_WORK(&sp->work, process_srcu);
- INIT_LIST_HEAD(&sp->srcu_boot_entry);
if (!is_static)
sp->sda = alloc_percpu(struct srcu_data);
init_srcu_struct_nodes(sp, is_static);
@@ -709,8 +708,8 @@ static void srcu_funnel_gp_start(struct srcu_struct *sp, struct srcu_data *sdp,
if (likely(srcu_init_done))
queue_delayed_work(rcu_gp_wq, &sp->work,
srcu_get_delay(sp));
- else if (list_empty(&sp->srcu_boot_entry))
- list_add(&sp->srcu_boot_entry, &srcu_boot_list);
+ else if (list_empty(&sp->work.work.entry))
+ list_add(&sp->work.work.entry, &srcu_boot_list);
}
spin_unlock_irqrestore_rcu_node(sp, flags);
}
@@ -1324,10 +1323,10 @@ void __init srcu_init(void)

srcu_init_done = true;
while (!list_empty(&srcu_boot_list)) {
- sp = list_first_entry(&srcu_boot_list,
- struct srcu_struct, srcu_boot_entry);
+ sp = list_first_entry(&srcu_boot_list, struct srcu_struct,
+ work.work.entry);
check_init_srcu_struct(sp);
- list_del_init(&sp->srcu_boot_entry);
+ list_del_init(&sp->work.work.entry);
queue_work(rcu_gp_wq, &sp->work.work);
}
}
--
2.17.1