linux-kernel - Re: [PATCH 0/8] x86, acpi: Move acpi_initrd

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Message-ID: <20130822202158.GD3490@mtj.dyndns.org>
Date:	Thu, 22 Aug 2013 16:21:58 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Toshi Kani <toshi.kani@...com>
Cc:	Zhang Yanfei <zhangyanfei.yes@...il.com>,
	Tang Chen <tangchen@...fujitsu.com>, konrad.wilk@...cle.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 0/8] x86, acpi: Move acpi_initrd_override() earlier.

Hello,

On Thu, Aug 22, 2013 at 02:11:32PM -0600, Toshi Kani wrote:
> It's too late for the kernel image itself, but it prevents allocating
> kernel memory from movable ranges after that.  I'd say it solves a half
> of the issue this time.

That works if such half solution eventually leads to the full
solution.  This is just a distraction.  You are already too late in
the boot sequence.  It doesn't even qualify as a half solution.  It's
like obsessing about a speck on your shirt without your trousers on.
If you want to solve this, do that from a place where it actually is
solvable.

> > > Also, how do you support local page tables without pursing SRAT early?
> > 
> > Does it even matter with huge mappings?  It's gonna be contained in a
> > single page anyway, right?
> 
> Are the huge mappings always used?  We cannot force user programs to use
> huge pages, can we?

Everything is a trade-off.  Should we do all this just to support the
off chance someone tries to use memory hotplug on a machine which
doesn't support huge mapping when virtually all CPUs on market
supports it?

> As for the maintainability, I am far more concerned with your suggestion
> of having a separate page table init code when SRAT is used.  This kind
> of divergence is a recipe of breakage.

I don't buy that.  The only thing which needs to change is the
directionality of allocation and we probably don't even need to do
that if huge mapping is in use.

Thanks.

-- 
tejun
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