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

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Message-ID: <20130625073819.GC11420@gmail.com>
Date:	Tue, 25 Jun 2013 09:38:19 +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


* Nathan Zimmer <nzimmer@....com> wrote:

> On Sun, Jun 23, 2013 at 11:28:40AM +0200, Ingo Molnar wrote:
> > 
> > That's 4.5 GB/sec initialization speed - that feels a bit slow and the 
> > boot time effect should be felt on smaller 'a couple of gigabytes' 
> > desktop boxes as well. Do we know exactly where the 2 hours of boot 
> > time on a 32 TB system is spent?
> 
> There are other several spots that could be improved on a large system 
> but memory initialization is by far the biggest.

My feeling is that deferred/on-demand initialization triggered from the 
buddy allocator is the better long term solution.

That will also make it much easier to profile/test memory init 
performance: boot up a large system and run a simple testprogram that 
allocates a lot of RAM.

( It will also make people want to optimize the initialization sequence 
  better, as it will be part of any freshly booted system's memory 
  allocation overhead. )

Thanks,

	Ingo
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