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

Steven Rostedt
2018-08-30T01:56:22Z

On Wed, 29 Aug 2018 14:23:13 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> 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), \

Thanks!

-- Steve

> __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);
> }
> }