linux-kernel - Re: [RFC:Patch: 000/008](memory hotplug) rough idea of pgdat removing

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Message-ID: <489314FE.7080900@linux-foundation.org>
Date:	Fri, 01 Aug 2008 08:51:58 -0500
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Yasunori Goto <y-goto@...fujitsu.com>
CC:	Badari Pulavarty <pbadari@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, linux-mm <linux-mm@...ck.org>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC:Patch: 000/008](memory hotplug) rough idea of pgdat removing

Yasunori Goto wrote:

> I thought it at first, but are there the following worst case?
> 
> 
>    CPU 0                                    CPU 1
> -------------------------------------------------------
> __alloc_pages()
>     
>     parsing_zonelist()
>         :
>     enter page_reclarim()
>     sleep (and remember zone)                 :
>                                               :
>                                         update zonelist and node_online_map
>                                           with stop_machine_run()
>                                         free pgdat().
>                                         remove the Node electrically.
> 
>     wake up and touch remembered
>        zone,  but it is removed
>     (Oops!!!)
> 
> 
> 
> Anyway, I'm happy if there is better way than my poor idea. :-)
> 
> Thanks for your comment.

Duh. Then the use of RCU would also mean that all of reclaim must be in a rcu period. So  reclaim cannot sleep anymore.



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