linux-kernel - Re: [RFC] Transparent on-demand memory setup initialization embedded in the (GFP) buddy allocator

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Message-ID: <20130626133715.GA6424@gmail.com>
Date:	Wed, 26 Jun 2013 15:37:15 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mike Travis <travis@....com>, "H. Peter Anvin" <hpa@...or.com>,
	Nathan Zimmer <nzimmer@....com>, holt@....com, rob@...dley.net,
	tglx@...utronix.de, mingo@...hat.com, yinghai@...nel.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] Transparent on-demand memory setup initialization embedded
 in the (GFP) buddy allocator


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Wed, 26 Jun 2013 11:22:48 +0200 Ingo Molnar <mingo@...nel.org> wrote:
> 
> > except that on 32 TB 
> > systems we don't spend ~2 hours initializing 8,589,934,592 page heads.
> 
> That's about a million a second which is crazy slow - even my 
> prehistoric desktop is 100x faster than that.
> 
> Where's all this time actually being spent?

See the earlier part of the thread - apparently it's spent initializing 
the page heads - remote NUMA node misses from a single boot CPU, going 
across a zillion cross-connects? I guess there's some other low hanging 
fruits as well - so making this easier to profile would be nice. The 
profile posted was not really usable.

Btw., NUMA locality would be another advantage of on-demand 
initialization: actual users of RAM tend to allocate node-local 
(especially on large clusters), so any overhead will be naturally lower.

Thanks,

	Ingo
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