linux-kernel - Re: [PATCH 0/3] bootmem2 III

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Message-ID: <87ve1gpumo.fsf@saeurebad.de>
Date:	Wed, 14 May 2008 21:12:47 +0200
From:	Johannes Weiner <hannes@...urebad.de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...e.hu>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/3] bootmem2 III

Hi Andi,

Andi Kleen <andi@...stfloor.org> writes:

>> I was wondering yesterday if it would be feasible to enforce
>> contiguousness for nodes.
>
> And lose the memory? That would make people not happy.

No, one node descriptor per contiguous block on the physical node.

So this setup:

node 0: 0-2G, 4-6G
node 1: 2-4G, 6-8G

would have 4 pgdats.

>> So that arch-code does not create one pgdat
>> for each node but one for each contiguous block.  I have not yet looked
>> deeper into it, but I suspect that other mm code has similar problems
>> with nodes spanning other nodes.
>
> I wouldn't think so. At least sparse memory with large holes is not that
> uncommon in the non x86 world.

I do not quite understand.  Holes are not the problem - the overlapping
is.

The current bootmem allocator for example might pass the same pfn twice
to the buddy allocator when two nodes overlap.  And I don't know if
other mm code has the same problem.

	Hannes
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