Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933792AbaFRDhH (ORCPT ); Tue, 17 Jun 2014 23:37:07 -0400 Received: from cn.fujitsu.com ([59.151.112.132]:16982 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S932192AbaFRDhF (ORCPT ); Tue, 17 Jun 2014 23:37:05 -0400 X-IronPort-AV: E=Sophos;i="5.00,729,1396972800"; d="scan'208";a="32066952" Message-ID: <53A1097F.3060400@cn.fujitsu.com> Date: Wed, 18 Jun 2014 11:37:35 +0800 From: Lai Jiangshan User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc14 Thunderbird/3.1.4 MIME-Version: 1.0 To: Tejun Heo CC: , , Subject: Re: [PATCH 6/6] percpu-refcount: implement percpu_ref_reinit() and percpu_ref_is_zero() References: <1403053685-28240-1-git-send-email-tj@kernel.org> <1403053685-28240-7-git-send-email-tj@kernel.org> In-Reply-To: <1403053685-28240-7-git-send-email-tj@kernel.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.167.226.103] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/18/2014 09:08 AM, Tejun Heo wrote: > Now that explicit invocation of percpu_ref_exit() is necessary to free > the percpu counter, we can implement percpu_ref_reinit() which > reinitializes a released percpu_ref. This can be used implement > scalable gating switch which can be drained and then re-opened without > worrying about memory allocation failures. > > percpu_ref_is_zero() is added to be used in a sanity check in > percpu_ref_exit(). As this function will be useful for other purposes > too, make it a public interface. > > Signed-off-by: Tejun Heo > Cc: Kent Overstreet > Cc: Christoph Lameter > --- > include/linux/percpu-refcount.h | 21 ++++++++++++++++++++- > lib/percpu-refcount.c | 35 +++++++++++++++++++++++++++++++++++ > 2 files changed, 55 insertions(+), 1 deletion(-) > > diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h > index 0ddd283..80f21ea 100644 > --- a/include/linux/percpu-refcount.h > +++ b/include/linux/percpu-refcount.h > @@ -67,6 +67,7 @@ struct percpu_ref { > > int __must_check percpu_ref_init(struct percpu_ref *ref, > percpu_ref_func_t *release); > +void percpu_ref_reinit(struct percpu_ref *ref); > void percpu_ref_exit(struct percpu_ref *ref); > void percpu_ref_kill_and_confirm(struct percpu_ref *ref, > percpu_ref_func_t *confirm_kill); > @@ -97,7 +98,10 @@ static inline void percpu_ref_kill(struct percpu_ref *ref) > static inline bool __pcpu_ref_alive(struct percpu_ref *ref, > unsigned __percpu **pcpu_countp) > { > - unsigned long pcpu_ptr = ACCESS_ONCE(ref->pcpu_count_ptr); > + unsigned long pcpu_ptr; > + > + /* paired with smp_store_release() in percpu_ref_reinit() */ > + pcpu_ptr = smp_load_acquire(&ref->pcpu_count_ptr); Does "smp_load_acquire()" hurts the performance of percpu_ref_get/put() in non-x86 system? > > if (unlikely(pcpu_ptr & PCPU_REF_DEAD)) > return false; > @@ -206,4 +210,19 @@ static inline void percpu_ref_put(struct percpu_ref *ref) > rcu_read_unlock_sched(); > } > > +/** > + * percpu_ref_is_zero - test whether a percpu refcount reached zero > + * @ref: percpu_ref to test > + * > + * Returns %true if @ref reached zero. > + */ > +static inline bool percpu_ref_is_zero(struct percpu_ref *ref) > +{ > + unsigned __percpu *pcpu_count; > + > + if (__pcpu_ref_alive(ref, &pcpu_count)) > + return false; > + return !atomic_read(&ref->count); > +} > + > #endif > diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c > index ac42991..b348a2f 100644 > --- a/lib/percpu-refcount.c > +++ b/lib/percpu-refcount.c > @@ -61,6 +61,41 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release) > EXPORT_SYMBOL_GPL(percpu_ref_init); > > /** > + * percpu_ref_reinit - re-initialize a percpu refcount > + * @ref: perpcu_ref to re-initialize > + * > + * Re-initialize @ref so that it's in the same state as when it finished > + * percpu_ref_init(). @ref must have been initialized successfully, killed > + * and reached 0 but not exited. > + * > + * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while > + * this function is in progress. > + */ > +void percpu_ref_reinit(struct percpu_ref *ref) > +{ > + unsigned __percpu *pcpu_count = pcpu_count_ptr(ref); > + int cpu; > + > + BUG_ON(!pcpu_count); > + WARN_ON(!percpu_ref_is_zero(ref)); > + > + atomic_set(&ref->count, 1 + PCPU_COUNT_BIAS); > + > + /* > + * Restore per-cpu operation. smp_store_release() is paired with > + * smp_load_acquire() in __pcpu_ref_alive() and guarantees that the > + * zeroing is visible to all percpu accesses which can see the > + * following PCPU_REF_DEAD clearing. > + */ > + for_each_possible_cpu(cpu) > + *per_cpu_ptr(pcpu_count, cpu) = 0; > + > + smp_store_release(&ref->pcpu_count_ptr, > + ref->pcpu_count_ptr & ~PCPU_REF_DEAD); > +} > +EXPORT_SYMBOL_GPL(percpu_ref_reinit); > + > +/** > * percpu_ref_exit - undo percpu_ref_init() > * @ref: percpu_ref to exit > * -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/