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Date: Tue, 23 Sep 2014 14:11:15 -0700
From: Kent Overstreet <kmo@...erainc.com>
To: Tejun Heo <tj@...nel.org>
Cc: linux-kernel@...r.kernel.org, axboe@...nel.dk, hch@...radead.org,
hannes@...xchg.org
Subject: Re: [PATCH 4/9] percpu_ref: rename things to prepare for decoupling
percpu/atomic mode switch
On Tue, Sep 23, 2014 at 01:55:13AM -0400, Tejun Heo wrote:
> percpu_ref will be restructured so that percpu/atomic mode switching
> and reference killing are dedoupled. In preparation, do the following
> renames.
>
> * percpu_ref->confirm_kill -> percpu_ref->confirm_switch
> * __PERCPU_REF_DEAD -> __PERCPU_REF_ATOMIC
> * __percpu_ref_alive() -> __ref_is_percpu()
>
> This patch is pure rename and doesn't introduce any functional
> changes.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Kent Overstreet <kmo@...erainc.com>
Reviewed-by: Kent Overstreet <kmo@...erainc.com>
> ---
> include/linux/percpu-refcount.h | 25 ++++++++++++++-----------
> lib/percpu-refcount.c | 22 +++++++++++-----------
> 2 files changed, 25 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
> index 3d463a3..910e5f7 100644
> --- a/include/linux/percpu-refcount.h
> +++ b/include/linux/percpu-refcount.h
> @@ -54,6 +54,11 @@
> struct percpu_ref;
> typedef void (percpu_ref_func_t)(struct percpu_ref *);
>
> +/* flags set in the lower bits of percpu_ref->percpu_count_ptr */
> +enum {
> + __PERCPU_REF_ATOMIC = 1LU << 0, /* operating in atomic mode */
> +};
> +
> struct percpu_ref {
> atomic_long_t count;
> /*
> @@ -62,7 +67,7 @@ struct percpu_ref {
> */
> unsigned long percpu_count_ptr;
> percpu_ref_func_t *release;
> - percpu_ref_func_t *confirm_kill;
> + percpu_ref_func_t *confirm_switch;
> struct rcu_head rcu;
> };
>
> @@ -88,23 +93,21 @@ static inline void percpu_ref_kill(struct percpu_ref *ref)
> return percpu_ref_kill_and_confirm(ref, NULL);
> }
>
> -#define __PERCPU_REF_DEAD 1
> -
> /*
> * Internal helper. Don't use outside percpu-refcount proper. The
> * function doesn't return the pointer and let the caller test it for NULL
> * because doing so forces the compiler to generate two conditional
> * branches as it can't assume that @ref->percpu_count is not NULL.
> */
> -static inline bool __percpu_ref_alive(struct percpu_ref *ref,
> - unsigned long __percpu **percpu_countp)
> +static inline bool __ref_is_percpu(struct percpu_ref *ref,
> + unsigned long __percpu **percpu_countp)
> {
> unsigned long percpu_ptr = ACCESS_ONCE(ref->percpu_count_ptr);
>
> /* paired with smp_store_release() in percpu_ref_reinit() */
> smp_read_barrier_depends();
>
> - if (unlikely(percpu_ptr & __PERCPU_REF_DEAD))
> + if (unlikely(percpu_ptr & __PERCPU_REF_ATOMIC))
> return false;
>
> *percpu_countp = (unsigned long __percpu *)percpu_ptr;
> @@ -125,7 +128,7 @@ static inline void percpu_ref_get(struct percpu_ref *ref)
>
> rcu_read_lock_sched();
>
> - if (__percpu_ref_alive(ref, &percpu_count))
> + if (__ref_is_percpu(ref, &percpu_count))
> this_cpu_inc(*percpu_count);
> else
> atomic_long_inc(&ref->count);
> @@ -149,7 +152,7 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref)
>
> rcu_read_lock_sched();
>
> - if (__percpu_ref_alive(ref, &percpu_count)) {
> + if (__ref_is_percpu(ref, &percpu_count)) {
> this_cpu_inc(*percpu_count);
> ret = true;
> } else {
> @@ -183,7 +186,7 @@ static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)
>
> rcu_read_lock_sched();
>
> - if (__percpu_ref_alive(ref, &percpu_count)) {
> + if (__ref_is_percpu(ref, &percpu_count)) {
> this_cpu_inc(*percpu_count);
> ret = true;
> }
> @@ -208,7 +211,7 @@ static inline void percpu_ref_put(struct percpu_ref *ref)
>
> rcu_read_lock_sched();
>
> - if (__percpu_ref_alive(ref, &percpu_count))
> + if (__ref_is_percpu(ref, &percpu_count))
> this_cpu_dec(*percpu_count);
> else if (unlikely(atomic_long_dec_and_test(&ref->count)))
> ref->release(ref);
> @@ -228,7 +231,7 @@ static inline bool percpu_ref_is_zero(struct percpu_ref *ref)
> {
> unsigned long __percpu *percpu_count;
>
> - if (__percpu_ref_alive(ref, &percpu_count))
> + if (__ref_is_percpu(ref, &percpu_count))
> return false;
> return !atomic_long_read(&ref->count);
> }
> diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
> index 5aea6b7..7aef590 100644
> --- a/lib/percpu-refcount.c
> +++ b/lib/percpu-refcount.c
> @@ -34,7 +34,7 @@
> static unsigned long __percpu *percpu_count_ptr(struct percpu_ref *ref)
> {
> return (unsigned long __percpu *)
> - (ref->percpu_count_ptr & ~__PERCPU_REF_DEAD);
> + (ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC);
> }
>
> /**
> @@ -80,7 +80,7 @@ void percpu_ref_exit(struct percpu_ref *ref)
>
> if (percpu_count) {
> free_percpu(percpu_count);
> - ref->percpu_count_ptr = __PERCPU_REF_DEAD;
> + ref->percpu_count_ptr = __PERCPU_REF_ATOMIC;
> }
> }
> EXPORT_SYMBOL_GPL(percpu_ref_exit);
> @@ -117,8 +117,8 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
> ref->release, atomic_long_read(&ref->count));
>
> /* @ref is viewed as dead on all CPUs, send out kill confirmation */
> - if (ref->confirm_kill)
> - ref->confirm_kill(ref);
> + if (ref->confirm_switch)
> + ref->confirm_switch(ref);
>
> /*
> * Now we're in single atomic_long_t mode with a consistent
> @@ -145,11 +145,11 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
> void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
> percpu_ref_func_t *confirm_kill)
> {
> - WARN_ONCE(ref->percpu_count_ptr & __PERCPU_REF_DEAD,
> + WARN_ONCE(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC,
> "%s called more than once on %pf!", __func__, ref->release);
>
> - ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
> - ref->confirm_kill = confirm_kill;
> + ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
> + ref->confirm_switch = confirm_kill;
>
> call_rcu_sched(&ref->rcu, percpu_ref_kill_rcu);
> }
> @@ -178,14 +178,14 @@ void percpu_ref_reinit(struct percpu_ref *ref)
>
> /*
> * Restore per-cpu operation. smp_store_release() is paired with
> - * smp_read_barrier_depends() in __percpu_ref_alive() and
> - * guarantees that the zeroing is visible to all percpu accesses
> - * which can see the following __PERCPU_REF_DEAD clearing.
> + * smp_read_barrier_depends() in __ref_is_percpu() and guarantees
> + * that the zeroing is visible to all percpu accesses which can see
> + * the following __PERCPU_REF_ATOMIC clearing.
> */
> for_each_possible_cpu(cpu)
> *per_cpu_ptr(percpu_count, cpu) = 0;
>
> smp_store_release(&ref->percpu_count_ptr,
> - ref->percpu_count_ptr & ~__PERCPU_REF_DEAD);
> + ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC);
> }
> EXPORT_SYMBOL_GPL(percpu_ref_reinit);
> --
> 1.9.3
>
--
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