linux-kernel - Re: [PATCH] x86-64: improve e820_search

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Message-ID: <4A049B99.4000402@zytor.com>
Date:	Fri, 08 May 2009 13:52:41 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Jan Beulich <jbeulich@...ell.com>, mingo@...e.hu,
	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86-64: improve e820_search_gap()

Andi Kleen wrote:
> On Fri, May 08, 2009 at 01:15:38PM -0700, H. Peter Anvin wrote:
>> Andi Kleen wrote:
>>> "Jan Beulich" <jbeulich@...ell.com> writes:
>>>> Why blindly? Aren't hotpluggable memory ranges supposed to be reserved
>>>> in the E820 map?
>>> They are supposed to be reserved in SRAT, but not in e820.
>> Ah, okay.  Perhaps we should fold this information into our internal 
>> "e820" map?  If so I guess the question is how soon we can do that.
> 
> You could do that or just query SRAT too, but ...
> 
> The problem is really that there are still systems which have hidden
> holes which are not reserved anywhere. When I last hacked on the gap algorithm
> it triggered subtle bugs. So this will never be fully reliable.
> 

That's without a question.

However, as far as querying SRAT, I don't like the idea of spreading the 
knowledge of the system memory map out between a bunch of different 
places, each of which have a little piece of the puzzle.  It puts a huge 
onus on the user to know what mechanisms are actually available, and 
really makes a shitty interface.

	-hpa
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