linux-kernel - Re: [PATCH 1/2] pcpu_ref: add percpu_ref_tryget

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Message-ID: <fe13d615-0fae-23e3-f133-49b727973d14@kernel.dk>
Date:   Tue, 17 Dec 2019 16:42:59 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 1/2] pcpu_ref: add percpu_ref_tryget_many()

CC Tejun on this one. Looks fine to me, and matches the put path.


On 12/17/19 3:28 PM, Pavel Begunkov wrote:
> Add percpu_ref_tryget_many(), which works the same way as
> percpu_ref_tryget(), but grabs specified number of refs.
> 
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> ---
>  include/linux/percpu-refcount.h | 24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
> index 390031e816dc..19079b62ce31 100644
> --- a/include/linux/percpu-refcount.h
> +++ b/include/linux/percpu-refcount.h
> @@ -210,15 +210,17 @@ static inline void percpu_ref_get(struct percpu_ref *ref)
>  }
>  
>  /**
> - * percpu_ref_tryget - try to increment a percpu refcount
> + * percpu_ref_tryget_many - try to increment a percpu refcount
>   * @ref: percpu_ref to try-get
> + * @nr: number of references to get
>   *
>   * Increment a percpu refcount unless its count already reached zero.
>   * Returns %true on success; %false on failure.
>   *
>   * This function is safe to call as long as @ref is between init and exit.
>   */
> -static inline bool percpu_ref_tryget(struct percpu_ref *ref)
> +static inline bool percpu_ref_tryget_many(struct percpu_ref *ref,
> +					  unsigned long nr)
>  {
>  	unsigned long __percpu *percpu_count;
>  	bool ret;
> @@ -226,10 +228,10 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref)
>  	rcu_read_lock();
>  
>  	if (__ref_is_percpu(ref, &percpu_count)) {
> -		this_cpu_inc(*percpu_count);
> +		this_cpu_add(*percpu_count, nr);
>  		ret = true;
>  	} else {
> -		ret = atomic_long_inc_not_zero(&ref->count);
> +		ret = atomic_long_add_unless(&ref->count, nr, 0);
>  	}
>  
>  	rcu_read_unlock();
> @@ -237,6 +239,20 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref)
>  	return ret;
>  }
>  
> +/**
> + * percpu_ref_tryget - try to increment a percpu refcount
> + * @ref: percpu_ref to try-get
> + *
> + * Increment a percpu refcount unless its count already reached zero.
> + * Returns %true on success; %false on failure.
> + *
> + * This function is safe to call as long as @ref is between init and exit.
> + */
> +static inline bool percpu_ref_tryget(struct percpu_ref *ref)
> +{
> +	return percpu_ref_tryget_many(ref, 1);
> +}
> +
>  /**
>   * percpu_ref_tryget_live - try to increment a live percpu refcount
>   * @ref: percpu_ref to try-get
> 


-- 
Jens Axboe