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From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Zhang\, Qiang" <Qiang.Zhang@windriver.com>,
        Waiman Long <longman@redhat.com>,
        "elver\@google.com" <elver@google.com>
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        "akpm\@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: =?utf-8?B?5Zue5aSNOiDlm57lpI06?= [PATCH] debugobjects: install
 cpu hotplug callback
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Date:   Wed, 26 Aug 2020 11:41:36 +0200
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On Wed, Aug 26 2020 at 08:34, Qiang Zhang wrote:

> ________________________________________
> =E5=8F=91=E4=BB=B6=E4=BA=BA: linux-kernel-owner@vger.kernel.org <linux-ke=
rnel-owner@vger.kernel.org> =E4=BB=A3=E8=A1=A8 Thomas Gleixner <tglx@linutr=
onix.de>
> =E5=8F=91=E9=80=81=E6=97=B6=E9=97=B4: 2020=E5=B9=B48=E6=9C=8826=E6=97=A5 =
7:53
> =E6=94=B6=E4=BB=B6=E4=BA=BA: Waiman Long; Zhang, Qiang; elver@google.com
> =E6=8A=84=E9=80=81: linux-kernel@vger.kernel.org; akpm@linux-foundation.o=
rg
> =E4=B8=BB=E9=A2=98: Re: =E5=9B=9E=E5=A4=8D: [PATCH] debugobjects: install=
 cpu hotplug callback

Can you please fix your mail client not to copy the headers into the
mail body? The headers are already in the mail itself.

> On Tue, Aug 25 2020 at 18:26, Waiman Long wrote:

Something like this is completely sufficient.

>>That's a really good question nevertheless. The only case where this
>>ever matters is physical hotplug. All other CPU hotplug stuff is
>>temporarily or in case of a late (post boottime) SMT disable it's going
>>to be a handful of free objects on that pool. As debugobjects is as the
>>name says a debug facility the benefit is questionable unless there is a
>>good reason to do so.
>
>  I don't know there may not be too many objects in the percpu pool,
>  but that doesn't mean they no need to be free, a CPU may never be
>  online after it is offline. some objects in percpu pool is never
>  free.

And this matters because? Because your fully debug enabled kernel will
have an uptime of years after disabling the CPU?

That said, I'm not opposed against this patch, but

     'we should free objects'

is not a convincing technical argument for doing this. If we want to
have that then please add proper technical arguments to the changelog.

Thanks,

        tglx