linux-kernel - Re: [patch -mm 3/5] x86_64: fixed-size remaining fake nodes

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Message-ID: <Pine.LNX.4.56.0701291032160.26116@hadoop0.corp.google.com>
Date:	Mon, 29 Jan 2007 10:38:45 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Andi Kleen <ak@...e.de>
cc:	Andrew Morton <akpm@...l.org>, Rohit Seth <rohitseth@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch -mm 3/5] x86_64: fixed-size remaining fake nodes

On Mon, 29 Jan 2007, Andi Kleen wrote:

> On Thursday 25 January 2007 22:37, David Rientjes wrote:
> > Any leftover memory is allocated
> > to a final node unless the command-line ends with a comma.
> 
> That sounds like syntactical vinegar and a nasty trap. Remember 
> that venus probe that got lost because of a wrong comma.
> Can you find some nicer syntax for that please? 
> 

The only other appropriate syntax that comes to mind is perhaps a 
command-line that ends with a 0.  For example, numa=fake=2*512,0 would 
allocate two 512M nodes and nothing for the remaining RAM.

> Also it's pretty complex. Are there use cases for all of this? 
> 

There are.  Configurable node sizes (i.e. 'numa=fake=512,4*128', etc) are 
the major concept and help to avoid the overhead associated with something 
like 64 nodes of 64M each on a 4G machine.  We've seen some inefficiencies 
with scanning through so many zone lists on page_alloc when we encounter a 
full node.  Additional support such as 'numa=fake=2*512,*128' are used 
more for machines where you're unsure of their total system RAM in the 
first place but want to make sure you have the node sizes you need.

		David
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