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

Paul E. McKenney
2018-08-30T03:23:26Z

On Wed, Aug 29, 2018 at 10:46:09PM -0400, Steven Rostedt wrote:
> On Wed, 29 Aug 2018 19:07:01 -0700
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
>
> > 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" <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!
> >
> > Glad you like it! Does it actually work for you? ;-)
>
> Oh, you want me to actually test it too? ;-)

;-) ;-) ;-)

> I'll try to add that in my todo list tomorrow.

Much appreciated!

Thanx, Paul

> -- Steve
>
> >
> > 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);
> > > > }
> > > > }
> > >
>