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

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Message-ID: <20191218162642.GC2914998@devbig004.ftw2.facebook.com>
Date:   Wed, 18 Dec 2019 08:26:42 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org, Dennis Zhou <dennis@...nel.org>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 1/2] pcpu_ref: add percpu_ref_tryget_many()

(cc'ing Dennis and Christoph and quoting whole body)

Pavel, can you please cc percpu maintainers on related changes?

The patch looks fine to me.  Please feel free to add my acked-by.

On Tue, Dec 17, 2019 at 04:42:59PM -0700, Jens Axboe wrote:
> 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
> 

-- 
tejun