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

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Date:   Wed, 12 Oct 2022 22:41:12 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Eric DeVolder <eric.devolder@...cle.com>
Cc:     Baoquan He <bhe@...hat.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 Wed, Oct 12, 2022 at 03:19:19PM -0500, Eric DeVolder wrote:
> We run here QEMU with the ability for 1024 DIMM slots.

QEMU, haha.

What is the highest count of DIMM slots which are hotpluggable on a
real, *physical* system today? Are you saying you can have 1K DIMM slots
on a board?

I hardly doubt that.

> So, for example, 1TiB requires 1024 DIMMs of 1GiB each with 128MiB
> memblocks, that results in 8K possible memory regions. So just going
> to 4TiB reaches 32K memory regions.

Lemme see if I understand this correctly: when a system like that
crashes, you want to kdump *all* those 4TiB in a vmcore? How long would
that dump take to complete? A day?

IOW, how does a realistic use case of this look like - not a QEMU one?

Thx.

-- 
Regards/Gruss,
    Boris.

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