linux-kernel - Re: [PATCH v2 0/5] Add movablecore

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Date:	Fri, 30 Nov 2012 14:19:33 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	"Luck, Tony" <tony.luck@...el.com>
CC:	Mel Gorman <mgorman@...e.de>, "H. Peter Anvin" <hpa@...or.com>,
	Jiang Liu <jiang.liu@...wei.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"rob@...dley.net" <rob@...dley.net>,
	"isimatu.yasuaki@...fujitsu.com" <isimatu.yasuaki@...fujitsu.com>,
	"laijs@...fujitsu.com" <laijs@...fujitsu.com>,
	"wency@...fujitsu.com" <wency@...fujitsu.com>,
	"linfeng@...fujitsu.com" <linfeng@...fujitsu.com>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>,
	"rientjes@...gle.com" <rientjes@...gle.com>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Len Brown <lenb@...nel.org>,
	"Wang, Frank" <frank.wang@...el.com>
Subject: Re: [PATCH v2 0/5] Add movablecore_map boot option

On 11/30/2012 06:58 AM, Luck, Tony wrote:
>> If any significant percentage of memory is in ZONE_MOVABLE then the memory
>> hotplug people will have to deal with all the lowmem/highmem problems
>> that used to be faced by 32-bit x86 with PAE enabled. 
> 
> While these problems may still exist on large systems - I think it becomes
> harder to construct workloads that run into problems.  In those bad old days
> a significant fraction of lowmem was consumed by the kernel ... so it was
> pretty easy to find meta-data intensive workloads that would push it over
> a cliff.  Here we  are talking about systems with say 128GB per node divided
> into 64GB moveable and 64GB non-moveable (and I'd regard this as a rather
> low-end machine).  Unless the workload consists of zillions of tiny processes
> all mapping shared memory blocks, the percentage of memory allocated to
> the kernel is going to be tiny compared with the old 4GB days.
> 

Which is a perfectly common workload for containers, where you can have
hundreds of machines (per node) being sold out to third parties, a lot
of them consuming every single bit of metadata they can.



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