linux-kernel - Re: [PATCH 2/4] memory-hotplug: add node_device

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Message-ID: <CAHGf_=qn4m6x95h5uV6jXibc0RmTH-1ZC17vSUTyTTXktfd23g@mail.gmail.com>
Date:	Fri, 5 Oct 2012 14:39:22 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc:	wency@...fujitsu.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, rientjes@...gle.com,
	liuj97@...il.com, len.brown@...el.com, benh@...nel.crashing.org,
	paulus@...ba.org, minchan.kim@...il.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 2/4] memory-hotplug: add node_device_release

> I have the reason to have to fill the node struct with 0 by memset.
> The node is a part of node struct array (node_devices[]).
> If we add empty release function for suppressing warning,
> some data remains in the node struct after hot removing memory.
> So if we re-hot adds the memory, the node struct is reused by
> register_onde_node(). But the node struct has some data, because
> it was not initialized with 0. As a result, more waning is shown
> by the remained data at hot addinig memory as follows:

Even though you call memset(0) at offline. It doesn't guarantee the memory
keep 0 until online. E.g. physical memory exchange during offline, bit
corruption
by cosmic ray, etc. So, you should fill zero at online phase explicitly if need.

The basic hotplug design is: you should forget everything at offline
and you shouldn't
assume any initialized data at online.

Thanks.
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