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From: Ming Lei <ming.lei@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: linux-kernel@vger.kernel.org,
	Jianchao Wang <jianchao.w.wang@oracle.com>,
	Kent Overstreet <kent.overstreet@gmail.com>,
	linux-block@vger.kernel.org
Subject: Re: [PATCH] percpu-refcount: relax limit on percpu_ref_reinit()
Date: Wed, 12 Sep 2018 00:34:44 +0800	[thread overview]
Message-ID: <20180911163443.GD10082@ming.t460p> (raw)
In-Reply-To: <20180911163032.GA2966370@devbig004.ftw2.facebook.com>

On Tue, Sep 11, 2018 at 09:30:32AM -0700, Tejun Heo wrote:
> On Wed, Sep 12, 2018 at 12:05:33AM +0800, Ming Lei wrote:
> > On Tue, Sep 11, 2018 at 08:49:59AM -0700, Tejun Heo wrote:
> > > On Tue, Sep 11, 2018 at 11:45:41PM +0800, Ming Lei wrote:
> > > > > So, this part seems wrong.  The function is called percpu_ref_reinit()
> > > > > - the refcnt is expected to be in its initial state with just the base
> > > > > ref once this function returns.  If you're removing the restriction on
> > > > 
> > > > But the comment says that 'Re-initialize @ref so that it's in the same
> > > > state as when it finished', and this invariant isn't changed with this
> > > > patch.
> > > 
> > > The comment goes "when perpcu_ref_init() finished".  The function is
> > > called re _init_.  It should put the ref in the initial state, right?
> > 
> > OK, I am fine to keep the behaviour for this API, will introduce a new helper
> > for NVMe.
> 
> Why aren't switch_to_atomic/percpu enough?

The blk-mq's use case is this _reinit is done on one refcount which was
killed via percpu_ref_kill(), so the DEAD flag has to be cleared.

> 
> > However, it is doable to switch to percpu mode from atomic mode when it
> > doesn't drop to zero, looks like sort of perpcu_ref_reinit(inherit_old_refcount).
> 
> Isn't that way more contorted than just switching operating modes?

As explained above.

Thanks,
Ming

  reply	other threads:[~2018-09-11 21:35 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-09 12:58 [PATCH] percpu-refcount: relax limit on percpu_ref_reinit() Ming Lei
2018-09-09 18:46 ` Bart Van Assche
2018-09-09 23:59   ` Ming Lei
2018-09-10  1:40 ` jianchao.wang
2018-09-10 16:11   ` Ming Lei
2018-09-11  1:48     ` jianchao.wang
2018-09-11  4:03       ` Ming Lei
2018-09-11  4:40         ` jianchao.wang
2018-09-11  4:40           ` jianchao.wang
2018-09-11  8:20           ` Ming Lei
2018-09-11 14:22             ` jianchao.wang
2018-09-11 13:44           ` Tejun Heo
2018-09-11 14:13             ` jianchao.wang
2018-09-10  1:54 ` jianchao.wang
2018-09-10 16:49 ` Tejun Heo
2018-09-11  0:00   ` Ming Lei
2018-09-11 13:48     ` Tejun Heo
2018-09-11 15:45       ` Ming Lei
2018-09-11 15:49         ` Tejun Heo
2018-09-11 16:05           ` Ming Lei
2018-09-11 16:30             ` Tejun Heo
2018-09-11 16:34               ` Ming Lei [this message]
2018-09-11 16:38                 ` Tejun Heo
2018-09-12  1:52                   ` Ming Lei
2018-09-12 15:53                     ` Tejun Heo
2018-09-12 22:11                       ` Ming Lei
2018-09-12 22:11                         ` Ming Lei
2018-09-18 12:49                         ` Tejun Heo
2018-09-18 12:49                           ` Tejun Heo
2018-09-19  2:51                           ` Ming Lei
2018-09-19  2:51                             ` Ming Lei
2018-09-19 20:36                             ` Tejun Heo
2018-09-19 20:36                               ` Tejun Heo
2018-09-18  3:21 ` jianchao.wang
2018-09-18  7:34   ` Ming Lei

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