linux-kernel - Re: [PATCH part5 0/7] Arrange hotpluggable memory as ZONE

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Message-ID: <20130815012133.GQ28628@htj.dyndns.org>
Date:	Wed, 14 Aug 2013 21:21:33 -0400
From:	Tejun Heo <tj@...nel.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Tang Chen <imtangchen@...il.com>,
	Tang Chen <tangchen@...fujitsu.com>, robert.moore@...el.com,
	lv.zheng@...el.com, rjw@...k.pl, lenb@...nel.org,
	tglx@...utronix.de, mingo@...e.hu, hpa@...or.com,
	akpm@...ux-foundation.org, trenn@...e.de, yinghai@...nel.org,
	jiang.liu@...wei.com, wency@...fujitsu.com, laijs@...fujitsu.com,
	isimatu.yasuaki@...fujitsu.com, izumi.taku@...fujitsu.com,
	mgorman@...e.de, minchan@...nel.org, mina86@...a86.com,
	gong.chen@...ux.intel.com, vasilis.liaskovitis@...fitbricks.com,
	lwoodman@...hat.com, riel@...hat.com, jweiner@...hat.com,
	prarit@...hat.com, zhangyanfei@...fujitsu.com,
	yanghy@...fujitsu.com, x86@...nel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH part5 0/7] Arrange hotpluggable memory as ZONE_MOVABLE.

Hello, KOSAKI.

On Wed, Aug 14, 2013 at 09:08:22PM -0400, KOSAKI Motohiro wrote:
...
> a fallback. Bogus and misguided fallback give a user false relief and they don't
> notice their mistake quickly. The answer is, there is the fundamental rule.
> We always said, "measure your system carefully, and setting option carefully too".
> I have no seen any reason to make exception in this case.

Ugh... that is one stupid rule.  Sure, there are cases when those
aren't avoidable but sticking to that when there are better ways to do
it is stupid.  Why would you make it finicky when you don't have to?
That makes no sense.

> Secondly, memory hotplug is now maintained I and kamezawa-san. Then, I much likely
> have a chance to get a hotplug related bug report. For protecting my life, I don't
> want get a false bug claim. Then, I wouldn't like to aim incomplete fallback. When
> an admin makes mistake, they should shoot their foot, not me!

Dude, it's not cool to cause users' machine to fail boot because you
want bug report.  You don't do that.  There are other ways to achieve
that.  When the kernel can't make all hotpluggable nodes hotpluggable
(I mean, it's not necessarily node aligned to begin with), generate
warning and a debug dump with appropriate log levels.

If you think causing users' machine fail boot indetermistically is
acceptable, you really shouldn't be maintaining anything.  What is
this?  Are you nuts?

> Thirdly, I haven't insist to aim verbose and kind messages as last breath. It much
> likely help users. 

I have no idea what you're trying to say.

> Last, we are now discussing hotplug feature. Then, we can assume hotpluggable machine.
> They have a hotplug interface in farmware by definition. So, you need to aim a magic.

This is by no way magic.  It's a band-aid feature which aims to
achieve some portion of functionality with minimal impact on the rest
of code / runtime overhead.  If you wanna nack the whole thing, be my
guest.

Thanks.

-- 
tejun
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