linux-kernel - Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support

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Message-ID: <Y0b9apyIs+RpSo1e@zn.tnic>
Date:   Wed, 12 Oct 2022 19:46:18 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Baoquan He <bhe@...hat.com>
Cc:     Eric DeVolder <eric.devolder@...cle.com>,
        Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>, david@...hat.com,
        linux-kernel@...r.kernel.org, x86@...nel.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,
        sourabhjain@...ux.ibm.com, linux-mm@...ck.org
Subject: Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support

On Sat, Oct 08, 2022 at 10:35:14AM +0800, Baoquan He wrote:
> Memory hptlug is not limited by a certin or a max number of memory
> regions, but limited by how large of the linear mapping range which
> physical can be mapped into.

Memory hotplug is not limited by some abstract range but by the *actual*
possibility of how many DIMM slots on any motherboard can hotplug
memory. Certainly not 32K.

So you can choose a sane default which covers *all* actual systems out
there.

> For the Kconfig CRASH_MAX_MEMORY_RANGES Eric added, it's meaningful to
> me to set a fixed value which is enough in reality.

Yes, exactly.

> For extreme testing with special purpose, it could be broken easily,
> people need decide by self whether the CONFIG_CRASH_MAX_MEMORY_RANGES
> is enlarged or not.

I don't want for people to decide on one more thing where they have to
go and read a bunch of specs just to know what is a good value. So we
should set a sane, *practical* upper limit and simply go with it.

Everything else is testing stuff and if you test the kernel, then you
can change limits and values and so on as you want to.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette