linux-kernel - Re: PROBLEM: __offline_isolated_pages may offline too many pages

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Date:	Wed, 15 Dec 2010 10:25:51 +0100
From:	Ingo Korb <ingo@...na.de>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	linux-mm@...ck.org, akpm@...ux-foundation.org, mel@....ul.ie,
	cl@...ux-foundation.org, yinghai@...nel.org, andi.kleen@...el.com,
	linux-kernel@...r.kernel.org
Subject: Re: PROBLEM: __offline_isolated_pages may offline too many pages

On 15.12.2010 01:21, KAMEZAWA Hiroyuki wrote:

> It's designed for offline memory section>  MAX_ORDER. pageblock_nr_pages
> is tend to be smaller than that.
>
> Do you see the problem with _exsisting_ user interface of memory hotplug ?
> I think we have no control other than memory section.

The existing, exported interface (remove_memory() - the check itself is 
in offline_pages()) only checks if both start and end of the 
to-be-removed block are aligned to pageblock_nr_pages. As you noted the 
actual size and alignment requirements in __offline_isolated_pages can 
be larger that that, so I think the checks in offline_pages() should be 
changed (if 1<<MAX_ORDER is always >= pageblock_nr_pages) or extended 
(if there can be any relation between the two).

-ik
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