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

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Date:	Wed, 26 Mar 2008 22:57:57 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
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

KAMEZAWA Hiroyuki wrote:
> 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.
>   

Ah, I see what it is.  I wasn't trying to add enough memory.  It adds in 
units of SECTION_SIZE_BITS, which is 2^30 on 32-bit PAE.  When I 
increase the initial balloon extension to PAGES_PER_SECTION pages, I 
make some more progress:

xen_balloon: Initialising balloon driver.
trying to reserve 262144 pages (1073741824 bytes) for balloon
bootmem alloc of 147456 bytes failed!
Kernel panic - not syncing: Out of memory
Pid: 1, comm: swapper Not tainted 2.6.25-rc7-x86-latest.git-dirty #361
 [<c01299dc>] panic+0x49/0x102
 [<c0647c3c>] __alloc_bootmem+0x24/0x29
 [<c0647c6d>] __alloc_bootmem_node+0x2c/0x34
 [<c044bd97>] zone_wait_table_init+0x45/0x95
 [<c0467258>] init_currently_empty_zone+0x1d/0xaa
 [<c01738ea>] __add_pages+0x88/0xdb
 [<c011c1a5>] arch_add_memory+0x25/0x2b
 [<c01737a9>] add_memory_resource+0x2f/0x36
 [<c064e487>] balloon_init+0x1b8/0x2b9
 [<c0635495>] kernel_init+0x137/0x292
 [<c063535e>] ? kernel_init+0x0/0x292
 [<c063535e>] ? kernel_init+0x0/0x292
 [<c0108b67>] kernel_thread_helper+0x7/0x10
 =======================


What's the rationale for setting SECTION_SIZE_BITS to 30?  Seems like a 
fairly large chunk.

    J
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