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Date: Thu, 16 Jan 2014 16:15:19 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
MIME-Version: 1.0
Subject: Re: [PATCH RESEND part2 v2 1/8] x86: get pg_data_t's memory from
 other node
References: <529D3FC0.6000403@cn.fujitsu.com> <529D4048.9070000@cn.fujitsu.com> <20140116171112.GB24740@suse.de>
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To: Mel Gorman <mgorman@suse.de>, Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>, Len Brown <lenb@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>, Toshi Kani <toshi.kani@hp.com>, Wanpeng Li <liwanp@linux.vnet.ibm.com>, Thomas Renninger <trenn@suse.de>, Yinghai Lu <yinghai@kernel.org>, Jiang Liu <jiang.liu@huawei.com>, Wen Congyang <wency@cn.fujitsu.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>, Taku Izumi <izumi.taku@jp.fujitsu.com>, Minchan Kim <minchan@kernel.org>, "mina86@mina86.com" <mina86@mina86.com>, "gong.chen@linux.intel.com" <gong.chen@linux.intel.com>, Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com>, "lwoodman@redhat.com" <lwoodman@redhat.com>, Rik van Riel <riel@redhat.com>, "jweiner@redhat.com" <jweiner@redhat.com>, Prarit Bhargava <prarit@redhat.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Linux MM <linux-mm@kvack.org>, Chen Tang <imtangchen@gmail.com>, Tang Chen <tangchen@cn.fujitsu.com>, Zhang Yanfei <zhangyanfei.yes@gmail.com>

On 01/16/2014 09:11 AM, Mel Gorman wrote:
> This implies that it is possible to ahve a configuration with a big ratio
> difference between Normal:Movable memory.

In fact, one would expect that would be the norm.

> In such configurations there
> would be a risk that the system will reclaim heavily or go OOM because
> the kernrel cannot allocate memory due to a relatively small Normal
> zone. What protects against that? Is the user ever warned if the ratio
> between Normal:Movable very high? The movable_node boot parameter still
> turns the feature on and off, there appears to be no way of controlling
> the ratio of memory other than booting with the minimum amount of memory
> and manually hot-adding the sections to set the appropriate ratio.

This is really the fundamental problem with this particular approach to
hotswap memory.

	-hpa



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