linux-kernel - Re: [PATCH 1/2 v2] x86: add max

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Message-ID: <4FD80923.1060807@zytor.com>
Date:	Tue, 12 Jun 2012 20:29:39 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	Wen Congyang <wency@...fujitsu.com>, rob@...dley.net,
	tglx@...utronix.de, Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	bhelgaas@...gle.com
Subject: Re: [PATCH 1/2 v2] x86: add max_addr boot option

On 06/12/2012 07:21 PM, Kamezawa Hiroyuki wrote:
> 
> But now, we know mem= boot option is buggy....it acts as max_addr=
> option, we have concerns that 'someone may fix mem= option as sane as ia64. because
> it's buggy".
> 
> We'd like to fix mem= boot option by ourselves and preserve old behavior
> with max_addr= boot option, which ia64 has.
> 

Now I'm *really* confused.

Realistically, there is no point in the old mem= behavior of assuming a
contiguous chunk of memory up to that point; it simply doesn't match how
modern hardware is constructed.  Your notion that ia64 is "sane" is
probably more of "outdated" in my opinion.

As such, the current behavior for mem= seems like the right thing and
the change was intentional (not to mention has been in place since
kernel 2.5.65, back in 2003); it also solves your requirements.  If you
are concerned about it, it would make more sense to make sure it is
documented as intentional.

In fact, it looks like IA64 introduced a divergence when the max_addr=
patch was introduced in 2004.  You're basically proposing the same
divergence for x86 now; talk about having the tail wag the dog.

Sorry.  NAK.

	-hpa

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