linux-kernel - Re: [PATCH v5 0/5] Add movablecore

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Date:	Wed, 16 Jan 2013 15:00:33 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	akpm@...ux-foundation.org, isimatu.yasuaki@...fujitsu.com,
	tony.luck@...el.com, tangchen@...fujitsu.com, jiang.liu@...wei.com,
	wujianguo@...wei.com, wency@...fujitsu.com, laijs@...fujitsu.com,
	linfeng@...fujitsu.com, yinghai@...nel.org, rob@...dley.net,
	minchan.kim@...il.com, mgorman@...e.de, rientjes@...gle.com,
	guz.fnst@...fujitsu.com, rusty@...tcorp.com.au, lliubbo@...il.com,
	jaegeuk.hanse@...il.com, glommer@...allels.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v5 0/5] Add movablecore_map boot option

On 01/16/2013 02:01 PM, KOSAKI Motohiro wrote:
>>>>
>>>> Things I'm wondering:
>>>>
>>>> - is there *really* a case for retaining the boot option if/when
>>>>    SRAT support is available?
>>>
>>> Yes. If SRAT support is available, all memory which enabled hotpluggable
>>> bit are managed by ZONEMOVABLE. But performance degradation may
>>> occur by NUMA because we can only allocate anonymous page and page-cache
>>> from these memory.
>>>
>>> In this case, if user cannot change SRAT information, user needs a way to
>>> select/set removable memory manually.
>>
>> If I understand this correctly you mean that once SRAT parsing is
>> implemented, the user can use movablecore_map to override that SRAT
>> parsing, yes?  That movablecore_map will take precedence over SRAT?
> 
> I think movablecore_map (I prefer movablemem than it, btw) should behave so.
> because of, for past three years, almost all memory hotplug bug was handled
> only I and kamezawa-san and, afaik, both don't have hotremove aware specific
> hardware.
> 
> So, if the new feature require specific hardware, we can't maintain this area
> any more.
>  

It is more so than that: the design principle should always be that
lower-level directives, if present, take precedence over higher-level
directives.  The reason for that should be pretty obvious: one of the
main uses of the low-level directives is to override the high-level
directives due to bugs or debugging needs.

	-hpa

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