linux-kernel - Re: [PATCH] memory hotplug: fix page_zone() calculation in test_pages

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Date:	Tue, 28 Oct 2008 14:00:01 +0100
From:	Gerald Schaefer <gerald.schaefer@...ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
	y-goto@...fujitsu.com
Subject: Re: [PATCH] memory hotplug: fix page_zone() calculation in
	test_pages_isolated()

On Tue, 2008-10-28 at 09:32 +0900, KAMEZAWA Hiroyuki wrote:
> But
>  - "pfn" and "end_pfn" (and pfn in the middle of them) can be in different zone on strange machine.
> 
> Now: test_pages_isolated() is called in following sequence.
>   
>   check_page_isolated()
>      walk_memory_resource()			# read resource range and get start/end of pfn
>          -> chcek_page_isolated_cb()
> 		-> test_page_isolated().
> 
> I think all pages within [start, end) passed to test_pages_isolated() should be in the same zone.
> 
> please change this to
>   check_page_isolated()
>      walk_memory_resource()
>          -> check_page_isolated_cb()
>                  -> walk_page_range_in_same_zone()  # get page range in the same zone.
>                         -> test_page_isolated().
> 
> Could you try ?

There is already a "same zone" check at the beginning of offline_pages():

>	if (!test_pages_in_a_zone(start_pfn, end_pfn))
>		return -EINVAL;

So we should be safe here, the only problem that I see is that my
zone->lock patch in test_pages_isolated() is broken. As explained,
the pfn used in my page_zone(pfn_to_page(pfn)) is >= end_pfn.

I'll send a new patch to fix this, using __first_valid_page() again,
as described in my reply to Daves mail. The only other solution that
I see would be to remember the first/last !NULL page that was found
inside the for() loop. Not sure which is better, but I think I like
the first one more. Any other ideas?

Thanks,
Gerald


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