linux-kernel - Re: [RFC 2/2] x86_64, mm: Reinsert the absent memory

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Message-ID: <20130623093250.GA13776@gmail.com>
Date:	Sun, 23 Jun 2013 11:32:50 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Nathan Zimmer <nzimmer@....com>
Cc:	holt@....com, travis@....com, rob@...dley.net, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, yinghai@...nel.org,
	akpm@...ux-foundation.org, gregkh@...uxfoundation.org,
	x86@...nel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC 2/2] x86_64, mm: Reinsert the absent memory


* Ingo Molnar <mingo@...nel.org> wrote:

> Yet another thing to consider would be to implement an initialization 
> speedup of 3 orders of magnitude: initialize on the large page (2MB) 
> grandularity and on-demand delay the initialization of the 4K granular 
> struct pages [but still allocating them] - which I suspect are a good 
> chunk of the overhead? That way we could initialize in 2MB steps and speed 
> up the 2 hours bootup of 32 TB of RAM to 14 seconds...
> 
> [ The cost would be one more branch in the buddy allocator, to detect
>   not-yet-initialized 2 MB chunks as we encounter them. Acceptable I 
>   think. ]

One advantage of this scheme would be that we could use it on pretty much 
any box, it would provide instant boot time speedups everywhere [a couple 
of hundred msecs on a small 4GB box - significant I think] - and would 
spread out and parallelize initialization to later stages.

Thanks,

	Ingo
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