linux-kernel - Re: [PATCH v21 2/7] crash: add generic infrastructure for crash hotplug support

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Date:   Wed, 19 Apr 2023 08:05:16 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Eric DeVolder <eric.devolder@...cle.com>, bp@...en8.de,
        x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        ebiederm@...ssion.com, dyoung@...hat.com, vgoyal@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        hpa@...or.com, nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org, david@...hat.com,
        sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com
Subject: Re: [PATCH v21 2/7] crash: add generic infrastructure for crash
 hotplug support

On 04/18/23 at 08:55am, Eric DeVolder wrote:
......
> > > > Seems we passed in the cpu number just for printing here. Wondering why
> > > > we don't print out hot added/removed memory ranges. Is the cpu number
> > > > printing necessary?
> > > > 
> > > Baoquan,
> > > 
> > > Ah, actually until recently it was used to track the 'offlinecpu' in this
> > > function, but tglx pointed out that was un-necessary. That resulted in
> > > dropping the code in this function dealing with offlinecpu, leaving this as
> > > its only use in this function.
> > > 
> > > The printing of cpu number is not necessary, but helpful; I use it for debugging.
> > 
> > OK, I see. I am not requesting memory range printing, just try to prove
> > cpu number printing is not so justified. If it's helpful, I am OK with
> > it. Let's see if other people have concern about this.
> > 
> 
> I do not plan on adding the memory range printing.
> 
> > > 
> > > The printing of memory range is also not necessary, but in order to do that,
> > > should we choose to do so, requires passing in the memory range to this
> > > function. This patch series did do this early on, and by v7 I dropped it at
> > > your urging (https://lore.kernel.org/lkml/20220401183040.1624-1-eric.devolder@oracle.com/).
> > > At the time, I provided it since I considered this generic infrastructure,
> > > but I could not defend it since x86 didn't need it. However, PPC now needs
> > > this, and is now carrying this as part of PPC support of CRASH_HOTPLUG (https://lore.kernel.org/linuxppc-dev/20230312181154.278900-6-sourabhjain@linux.ibm.com/T/#u).
> > > 
> > > If you'd rather I pickup the memory range handling again, I can do that. I
> > > think I'd likely change this function to be:
> > > 
> > >    void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu,
> > >       struct memory_notify *mhp);
> > > 
> > > where on a CPU op the 'cpu' parameter would be valid and 'mhp' NULL, and on a memory op,
> > > the 'mhp' would be valid and 'cpu' parameter invalid(0).
> > > 
> > > I'd likely then stuff these two parameters into struct kimage so that it can
> > > be utilized by arch-specific handler, if needed.
> > > 
> > > And of course, would print out the memory range for debug purposes.
> > > 
> > > Let me know what you think.
> > 
> 
> I do not plan on adding the memory range handling; I'll let Sourabh do that as he has a use case for it.
> 
> As such, I don't see any other request for changes.

OK, then I have no concern about this patchset. Thanks a lot for all
these effort, Eric.

Hi x86 maintainers,

Could you help check if there's anything we need improve, or consider
taking this patchset?

Thanks
Baoquan