linux-kernel - Re: [RFC 0/2] Delay initializing of large sections of memory

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Message-ID: <51C9E83A.8070700@sgi.com>
Date:	Tue, 25 Jun 2013 11:58:02 -0700
From:	Mike Travis <travis@....com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Yinghai Lu <yinghai@...nel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Nathan Zimmer <nzimmer@....com>, Robin Holt <holt@....com>,
	Rob Landley <rob@...dley.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-doc@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 0/2] Delay initializing of large sections of memory



On 6/25/2013 11:44 AM, H. Peter Anvin wrote:
> On 06/25/2013 11:40 AM, Yinghai Lu wrote:
>> On Tue, Jun 25, 2013 at 11:17 AM, H. Peter Anvin <hpa@...or.com> wrote:
>>> On 06/25/2013 10:35 AM, Mike Travis wrote:
>>
>>> However, please consider Ingo's counterproposal of doing this via the
>>> buddy allocator, i.e. hugepages being broken on demand.  That is a
>>> *very* powerful model, although would require more infrastructure.
>>
>> Can you or Ingo elaborate more about the buddy allocator proposal?
>>
> 
> Start by initializing 1G hyperpages only, but mark them so that the
> allocator knows that if it needs to break them apart it has to
> initialize the page structures for the 2M subpages.
> 
> Same thing with 2M -> 4K.
> 
> 	-hpa
> 
> 

It is worth experimenting with but the big question would be,
if it still avoids the very expensive "memmap_init_zone" and
it's sub-functions using huge expanses of memory.  I'll do some
experimenting as soon as I can.  Our 32TB system is being
brought back to 16TB (we found a number of problems as we
get closer and closer to the 64TB limit), but that's still
a significant size.
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