Re: [PATCH 1/2] pcpu_ref: add percpu_ref_tryget_many()

Pavel Begunkov
2019-12-21T15:37:03Z

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On 18/12/2019 20:49, Dennis Zhou wrote:
> On Wed, Dec 18, 2019 at 08:26:42AM -0800, Tejun Heo wrote:
>> (cc'ing Dennis and Christoph and quoting whole body)
>>
>> Pavel, can you please cc percpu maintainers on related changes?

My bad, lost cc's in the way.

>>
>> 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.

Thanks both for taking a look!

>>>
>>>
>>> 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@gmail.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.
>
> Minor nit: would be nice to change this so the two don't have identical
> comments. (eg: Increment a percpu refcount by @nr unless...)
>>>> *
>>>> * 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
>
> Acked-by: Dennis Zhou <dennis@kernel.org>
>
> Thanks,
> Dennis
>

--
Pavel Begunkov

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