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

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Date:	Thu, 27 Mar 2008 13:54:52 -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 22:57:57 -0700
> Jeremy Fitzhardinge <jeremy@...p.org> wrote:
>
>   
>> 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.
>>
>>     
> At first, I believe usual DIMM size is bigger than SECTION_SIZE_BITS. This is
> designed for hardware-based hotplug.
>
> If you want to use memory-hotplug for virtualized enviroment, it's good to make
> this to be smaller chunk. Powerpc/IBM lpar uses 16MB chunk.
>
> It's a trade-off between section mainainance cost v.s. size of plugged memory.
> please find the best.

Hm, I tried reducing it to 2^28 (=256M), but I get a compilation failure:

  CC      arch/x86/kernel/asm-offsets.s
In file included from /home/jeremy/hg/xen/paravirt/linux/include/linux/suspend.h:11,
                 from /home/jeremy/hg/xen/paravirt/linux/arch/x86/kernel/asm-offsets_32.c:11,
                 from /home/jeremy/hg/xen/paravirt/linux/arch/x86/kernel/asm-offsets.c:2:
/home/jeremy/hg/xen/paravirt/linux/include/linux/mm.h:458:2: error: #error SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > FLAGS_RESERVED
make[3]: *** [arch/x86/kernel/asm-offsets.s] Error 1


2^29 works.

    J

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