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

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Message-ID: <20090510151804.GE23223@one.firstfloor.org>
Date:	Sun, 10 May 2009 17:18:04 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	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()

On Sat, May 09, 2009 at 11:43:26PM -0700, H. Peter Anvin wrote:
> Andi Kleen wrote:
> >> 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.
> > 
> > AFAIK another popular OS always combines mappings from all sources (e820,
> > SRAT, PCI, PNP, ACPI etc.) in the query before allocating anything.
> > Something like that might be a reasonable long term direction for Linux
> > too, but it's probably also a can of worms to handle the conflicts
> > between the various sources (e.g. e820 reserves a lot of things
> > in other sources too). It would be a rather large change.
> > Maybe that would handle the systems I thought of above.
> 
> You *always* have a conflict resolution policy... whether or not it is

Well right now we ignore ACPI/PNP data, sometimes ignore PCI data 
and only look in e820 and sometimes only use PCI/e820 and sometimes
only use SRAT (or at least it was like this at some point)

BTW SRAT hot range can be also wrong, some BIOS always had a full
512GB range even though they don't support hotplug.
However I haven't seen a system which supports hotplug (not that
there are very many of those) where the entry was not there, so at least
that one should be safe.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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