linux-kernel - Re: Trying to make use of hotplug memory for xen balloon driver

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Message-Id: <20080327095059.5d2759a3.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 27 Mar 2008 09:50:59 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Yasunori Goto <y-goto@...fujitsu.com>,
	Christoph Lameter <clameter@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: Trying to make use of hotplug memory for xen balloon driver

On Wed, 26 Mar 2008 16:11:54 -0700
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Hi,
> 
> I'm trying to make use of hotplug memory in the Xen balloon driver.  If 
> you want to expand a domain to be larger than its initial size, it must 
> add new page structures to describe the new memory.
> 
> The platform is x86-32, with CONFIG_SPARSEMEM and 
> CONFIG_HOTPLUG_MEMORY.  Because the new memory is only pseudo-physical, 
> the physical address within the domain is arbitrary, and I added a 
> add_memory_resource() function so I could use allocate_resource() to 
> find an appropriate address to put the new memory at.
> 
welcome to chaos of memory hotplug :)

>    1. the online_page() raises an error:
> 
>       Bad page state in process 'events/0'
>       page:c16fa0cc flags:0x00000000 mapping:00000000 mapcount:1 count:0
>       Trying to fix it up, but a reboot is needed

Hmm, this seems memmap is not initialized correctly...
page->flags == 0 means page is in ZONE_DMA.(it's only 16MB range on x86)
I think memmap is not initilalized.

Calling path to memmap initailization is.
==
  add_memory()
	-> arch_add_memory()
		->  __add_page()
			-> __add_section()
				-> __add_zone()
					-> memmap_init_zone() 
==
Please check what arch_add_memory() is called, at first.



>    2. The new pages don't appear to be in the right zone.  When I boot a
>       256M domain I get an initial setup of:
> 
>       Zone PFN ranges:
>         DMA             0 ->     4096
>         Normal       4096 ->    65536
>         HighMem     65536 ->    65536
>       Movable zone start PFN for each node
>       early_node_map[1] active PFN ranges
>           0:        0 ->    65536
>       On node 0 totalpages: 65536
>         DMA zone: 52 pages used for memmap
>         DMA zone: 0 pages reserved
>         DMA zone: 4044 pages, LIFO batch:0
>         Normal zone: 780 pages used for memmap
>         Normal zone: 60660 pages, LIFO batch:15
>         HighMem zone: 0 pages used for memmap
>         Movable zone: 0 pages used for memmap
>           
> 
>       which presumably means that new pages above pfn 65536 should be in
>       the highmem zone?  But PageHighMem() returns false for those pages.
> 
See x86-32's arch_add_memory(). It's now designed that "all new memory will go into
ZONE_HIGHMEM".
(Because added memory is tend to be removed later.)

Thanks,
-Kame


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