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

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Date:	Wed, 26 Jun 2013 09:15:07 -0700
From:	Mike Travis <travis@....com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"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



On 6/26/2013 6:37 AM, Ingo Molnar wrote:
> 
> * 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.

This is one advantage of delayed memory init.  I can do it under
the profiler.  I will put everything together to accomplish this
and then send a perf report.

> 
> 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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