On Wed, Aug 29, 2018 at 09:56:16PM -0400, Steven Rostedt wrote:
> On Wed, 29 Aug 2018 14:23:13 -0700
> "Paul E. McKenney" <paul...@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 <rost...@goodmis.org>
> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> > Cc: Tejun Heo <t...@kernel.org>
> > Cc: Lai Jiangshan <jiangshan...@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!
Glad you like it! Does it actually work for you? ;-)
Thanx, Paul
> -- 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);
> > }
> > }
>
