linux-kernel - Re: [PATCH] memory_hotplug: always initialize pageblock bitmap.

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Message-Id: <20080509153910.6b074a30.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 9 May 2008 15:39:10 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Whitcroft <apw@...dowen.org>,
	Dave Hansen <haveblue@...ibm.com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] memory_hotplug: always initialize pageblock bitmap.

On Fri, 9 May 2008 08:06:09 +0200
Heiko Carstens <heiko.carstens@...ibm.com> wrote:

> From: Heiko Carstens <heiko.carstens@...ibm.com>
> 
> Trying to online a new memory section that was added via memory hotplug
> sometimes results in crashes when the new pages are added via
> __free_page. Reason for that is that the pageblock bitmap isn't
> initialized and hence contains random stuff.

Hmm, curious. In my understanding, memmap_init_zone() initializes it.

 __add_pages()
	-> __add_section()
		-> sparse-add_one_section() // allocate usemap
		-> __add_zone()
			-> memmap_init_zone() // reset pageblock's bitmap 

Can't memmap_init_zone() does proper initialization ?
........................
Ah, ok. I see. grow_zone_span() is not called at __add_zone(), then,
memmap_init_zone() doesn't initialize usemap because memmap is not in zone's
range.

Recently, I added a check "zone's start_pfn < pfn < zone's end"
to memmap_init_zone()'s usemap initialization for !SPARSEMEM case bug FIX.
(and I think the fix itself is sane.)

How about calling grow_pgdat_span()/grow_zone_span() from __add_zone() ?

Thanks,
-Kame

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