linux-kernel - Re: [PATCH V8 5/8] percpu-refcount: introduce __percpu_ref_tryget

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Message-ID: <20171003192412.GC5362@ming.t460p>
Date:   Wed, 4 Oct 2017 03:24:13 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Bart Van Assche <Bart.VanAssche@....com>
Cc:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "jejb@...ux.vnet.ibm.com" <jejb@...ux.vnet.ibm.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "axboe@...com" <axboe@...com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jthumshirn@...e.de" <jthumshirn@...e.de>,
        "martin@...htvoll.de" <martin@...htvoll.de>,
        "oleksandr@...alenko.name" <oleksandr@...alenko.name>,
        "hare@...e.com" <hare@...e.com>, "tj@...nel.org" <tj@...nel.org>,
        "cavery@...hat.com" <cavery@...hat.com>
Subject: Re: [PATCH V8 5/8] percpu-refcount: introduce
 __percpu_ref_tryget_live

On Tue, Oct 03, 2017 at 06:40:24PM +0000, Bart Van Assche wrote:
> On Tue, 2017-10-03 at 22:04 +0800, Ming Lei wrote:
> > Block layer need to call this function after holding
> > rcu lock in a real hot path, so introduce this helper.
> 
> Since it is allowed to nest rcu_read_lock_sched() calls I don't think
> that this patch is necessary.

Yeah, I know that, with this patch, we can avoid the nest RCU lock.
As I mentioned, it is a real hot path, so maybe better to not
introduce the extra RCU read lock/unlock.

If you guys doesn't care the little cost, I can remove that.

-- 
Ming