Re: [PATCH 21/24] rcu/tiny: move kvfree_call_rcu() out of header

Paul E. McKenney
2020-05-01T23:04:02Z

On Tue, Apr 28, 2020 at 10:59:00PM +0200, Uladzislau Rezki (Sony) wrote:
> Move inlined kvfree_call_rcu() function out of the
> header file. This step is a preparation for head-less
> support.
>
> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> ---
> include/linux/rcutiny.h | 6 +-----
> kernel/rcu/tiny.c | 6 ++++++
> 2 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> index 0c6315c4a0fe..7eb66909ae1b 100644
> --- a/include/linux/rcutiny.h
> +++ b/include/linux/rcutiny.h
> @@ -34,11 +34,7 @@ static inline void synchronize_rcu_expedited(void)
> synchronize_rcu();
> }
>
> -static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> -{
> - call_rcu(head, func);
> -}
> -
> +void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func);
> void rcu_qs(void);
>
> static inline void rcu_softirq_qs(void)
> diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
> index aa897c3f2e92..508c82faa45c 100644
> --- a/kernel/rcu/tiny.c
> +++ b/kernel/rcu/tiny.c
> @@ -177,6 +177,12 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func)
> }
> EXPORT_SYMBOL_GPL(call_rcu);
>
> +void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> +{
> + call_rcu(head, func);
> +}
> +EXPORT_SYMBOL_GPL(kvfree_call_rcu);

This increases the size of Tiny RCU. Plus in Tiny RCU, the overhead of
synchronize_rcu() is exactly zero. So why not make the single-argument
kvfree_call_rcu() just unconditionally do synchronize_rcu() followed by
kvfree() or whatever? That should go just fine into the header file.

Thanx, Paul

> void __init rcu_init(void)
> {
> open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
> --
> 2.20.1
>