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From: "jianchao.wang" <jianchao.w.wang@oracle.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>,
	Kent Overstreet <kent.overstreet@gmail.com>,
	linux-block@vger.kernel.org
Subject: Re: [PATCH] percpu-refcount: relax limit on percpu_ref_reinit()
Date: Tue, 11 Sep 2018 12:40:36 +0800	[thread overview]
Message-ID: <771fa1eb-85d3-2ff2-6070-207874da85b6@oracle.com> (raw)
In-Reply-To: <20180911040323.GC30977@ming.t460p>

Hi Ming

On 09/11/2018 12:03 PM, Ming Lei wrote:
> After the refcount is switched to atomic mode, the whole counting is
> done on the atomic part. Then if the refcount need to switch to percpu mode
> again, all percpu part of the counter is re-initialized as zero simply. This
> is invariant with/without this patch.

Does the "whole counting" here means ?

(long)(sum (every cpu's refcounter)) + atomic refcounter

and when switch to atomic mode, there could be value left in atomic refcounter.
then the unsigned long percpu refcounter cound be decreased from 0.
	
>From another angle, one request could be ended on a different cpu from the one where
it is issued.

Thanks
Jianchao

WARNING: multiple messages have this Message-ID (diff)
From: "jianchao.wang" <jianchao.w.wang@oracle.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>,
	Kent Overstreet <kent.overstreet@gmail.com>,
	linux-block@vger.kernel.org
Subject: Re: [PATCH] percpu-refcount: relax limit on percpu_ref_reinit()
Date: Tue, 11 Sep 2018 12:40:36 +0800	[thread overview]
Message-ID: <771fa1eb-85d3-2ff2-6070-207874da85b6@oracle.com> (raw)
In-Reply-To: <20180911040323.GC30977@ming.t460p>

Hi Ming

On 09/11/2018 12:03 PM, Ming Lei wrote:
> After the refcount is switched to atomic mode, the whole counting is
> done on the atomic part. Then if the refcount need to switch to percpu mode
> again, all percpu part of the counter is re-initialized as zero simply. This
> is invariant with/without this patch.

Does the "whole counting" here means ?

(long)(sum (every cpu's refcounter)) + atomic refcounter

and when switch to atomic mode, there could be value left in atomic refcounter.
then the unsigned long percpu refcounter cound be decreased from 0.
	
From another angle, one request could be ended on a different cpu from the one where
it is issued.

Thanks
Jianchao

  reply	other threads:[~2018-09-11  9:38 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 [this message]
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
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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