linux-kernel - Re: live kernel upgrades (was: live kernel patching design)

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Date:	Tue, 24 Feb 2015 13:28:48 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Ingo Molnar <mingo@...nel.org>,
	Arjan van de Ven <arjanvandeven@...il.com>
CC:	Dave Airlie <airlied@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Vojtech Pavlik <vojtech@...e.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Borislav Petkov <bp@...en8.de>, live-patching@...r.kernel.org
Subject: Re: live kernel upgrades (was: live kernel patching design)

On 02/24/2015, 10:16 AM, Ingo Molnar wrote:
> and we don't design the Linux kernel for weird, extreme 
> cases, we design for the common, sane case that has the 
> broadest appeal, and we hope that the feature garners 
> enough interest to be maintainable.

Hello,

oh, so why do we have NR_CPUS up to 8192, then? I haven't met a machine
with more than 16 cores yet. You did. But you haven't met a guy
thanksgiving for a live patching being so easy to implement, but fast. I
did.

What ones call extreme, others accept as standard. That is, I believe,
why you signed under the support for up to 8192 CPUs.

We develop Linux to be scalable, i.e. used on *whatever* scenario you
can imagine in any world. Be it large/small machines, lowmem/higmem,
numa/uma, whatever. If you don't like something, you are free to disable
that. Democracy.

> This is not a problem in general: the weird case can take 
> care of itself just fine - 'specialized and weird' usually 
> means there's enough money to throw at special hardware and 
> human solutions or it goes extinct quickly ...

Live patching is not a random idea which is about to die. It is months
of negotiations with customers, management, between developers,
establishing teams and really thinking about the idea. The decisions
were discussed on many conferences too. I am trying to shed some light
on why we are not trying to improve criu or any other already existing
project. We studied papers, codes, implementations, kSplice and such and
decided to incline to what we have implemented, presented and merged.

thanks,
-- 
js
suse labs
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