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

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Message-ID: <51C9E4B7.2000007@zytor.com>
Date:	Tue, 25 Jun 2013 11:43:03 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mike Travis <travis@....com>
CC:	Ingo Molnar <mingo@...nel.org>, Nathan Zimmer <nzimmer@....com>,
	holt@....com, rob@...dley.net, tglx@...utronix.de,
	mingo@...hat.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

On 06/25/2013 10:22 AM, Mike Travis wrote:
> 
> On 6/25/2013 12:38 AM, Ingo Molnar wrote:
>>
>> * 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.
> 
> I haven't caught up with all of Nathan's changes yet (just
> got back from vacation), but there was an option to either
> start the memory insertion on boot, or trigger it later
> using the /sys/.../memory interface.  There is also a monitor
> program that calculates the memory insertion rate.  This was
> extremely useful to determine how changes in the kernel
> affected the rate.
> 

Sorry, I *totally* did not follow that comment.  It seemed like a
complete non-sequitur?

	-hpa


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