linux-kernel - Re: [PATCH 4/4] x86_64: increse MAX_EARLY_RES for NODE

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Date:	Thu, 31 Jan 2008 14:34:30 +0100
From:	Andi Kleen <ak@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Yinghai Lu <Yinghai.Lu@....com>,
	Christoph Lameter <clameter@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 4/4] x86_64: increse MAX_EARLY_RES for NODE_DATA and bootmap

On Thursday 31 January 2008 14:24:38 Ingo Molnar wrote:
> 
> * Yinghai Lu <Yinghai.Lu@....COM> wrote:
> 
> > ok, discard 3, and 4.
> > 
> > how about 2 v2?
> 
> i'm leaning towards v4, but the more fundamental breakage is in the 
> early_node_mem() ad-hoc allocator that got butchered into this code a 
> year ago:

No it has nothing to do with early_node_mem which is just a thin
wrapper around find_e820_area() anyways.

I think the problem is that the page alignment in bad_addr() and friends is not 
always correct. e.g. the early_reserve for the kernel in head64.c really need to 
round up to pages. I suspect (not 100% sure yet that is the core of the problem) 

Note this was broken even before early reservation; the only difference
was that it was all hard coded in bad_addr() then.

There were various hacks around this in the past, but none fixed the problem 
completely.

>   commit a8062231d80239cf3405982858c02aea21a6066a
>   Author: Andi Kleen <ak@...e.de>
>   Date:   Fri Apr 7 19:49:21 2006 +0200
> 
>       [PATCH] x86_64: Handle empty PXMs that only contain hotplug memory
> 
>   ...
>   +static void * __init
>   +early_node_mem(int nodeid, unsigned long start, unsigned long end,
>   +             unsigned long size)
> 
> and we are now suffering the side-effects of that hack.
> 
> what i suspect we need instead is a proper early-allocator that works in 
> the e820 space.

That is find_e820_area() or rather find_e820_area+early_reserve now.

I had this implemented as a shrink wrapped function earlier for lockdep too, 
but dropped the patch because there was a nasty ordering issue with the e820 
command line parsing that i could not easily resolve.

-Andi
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