linux-kernel - Re: [PATCH] percpu-refcount: relax limit on percpu_ref

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

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